Another cheap scope: $18, shipped! (FNIRSI DSO152)

well hello everyone and welcome back to adrien's digital basement on today's video we're going to be taking a look at a very inexpensive piece of test equipment back in the day when you were working on electronics you might use something like this this is a logic probe and what you do is you connect it up to power you touch the probe tip to the electronics or testing say a leg of an IC and this little device will beep to tell you if the signal is high or low or changing well back in the day when oscilloscopes were very expensive you would use one of those things as an aid for testing because it's more useful than say a multimeter but still not as good as an oscilloscope but they were very expensive of course in this day and age we have stuff like this and this this one I've reviewed in my right hand here and these are very inexpensive portable oscilloscopes this is the more recent one that's going around for about 80 bucks you've probably seen this on some other channels and it's a decent piece of test equipment and I still actually prefer my hand tech there but that's not the subject of this video the subject of this video is I want to talk about this little thing here which is is a mini pocket handheld oscilloscope and I paid a total of $18 for this in fact today I went out for lunch and I paid more for my lunch than this thing cost shipped to my doorstep I know I still have viewers that don't have an oscilloscope even one of these inexpensive ones that cost $80 and I want to see if something that cost less than lunch is actually good enough to fix a computer so without further Ado let's get right to it [Music] so I have my cheap and inexpensive test gear here starting from left to right so of course on the left is the hand Tech oscilloscope I made a review of this a while ago of course I'll link to any reviews I have for stuff down in the description below I really like this scope it has a slightly funky user interface but this oscilloscope is an actual piece of test equipment that has specs that aren't made up and it really does work the design of this is kind of old though I think this thing came out maybe in 2016 2017 something like that and oddly enough it does charge the internal battery off USB typc so that's a little funny for something as old as this but because of that the screen is kind of low resolution it's a little chunky looking and the whole thing is really well built but the user interface is just a little sluggish and a little bit funny this is the new hotness here The Zo something or other of channels to review this as I mentioned it works pretty well actually I think the specs on this are kind of fake and kind of made up but yeah it absolutely does work I did find when I did a little bit of testing on this and I made a video for my patrons there are some weird idiosyncrasies on this device that caused some erroneous readings and for me personally if you have a piece of test equipment that you can't necessarily trust H that's really not a great thing I've never been let down by this particular scope it generally seems to work perfectly I think it occasionally has crashed on me like where it just sort of shuts off but I've never had erroneous readings out of it but I cannot say the same for the Zoe now that's not to say a firmware update couldn't fix those issues and you know if you watch the videos on this thing it has a pretty easy to use interface and that does work I once you just can work around the little strange idiosyncrasies that this thing has it's also pretty well built pretty small and only being $80 it's a really pretty good deal this scope though which they still do sell is down to I think 90 something dollar so it's come down from the 120 or so that I paid for it originally when I reviewed it and I'm sure the release of this has caused the price of the hand Tech to come down because this is well more bang for your buck and still is a bit cheaper but I'd actually still recommend this scope it has features that this thing doesn't have and you I like to use this thing it works quite well next is the logic probe as I mentioned and these things have been around forever I think going back to the 70s it's a simple piece of electronics you can connect this up to well I think all the way up to 12 volts or maybe even more than that and yeah it will beep and make flashy lights and things going on and it's a decent piece of test equipment but for me personally I would never use this over an oscilloscope it might be useful if you're just quickly spot checking something and you're listening for the audio cues that this makes because of course you have to look at these and meanwhile with this you can just listen but I don't think these are actually that great for troubleshooting it's better than nothing but it's certainly not going to be as good as these and that's because a lot of times I am looking at the oscilloscope to try to find something like a bus conflict or a signal that is not all the way up at 5 volts it might be only at like 1.5 volts and that tells me that there's something going on in the motherboard like there's a bad output driver or there's a short and these are all things you can't really detect very easily with these simple logic probes now these things I I mean they may have come down in price now but you know back in the day you'd spend 30 40 50 $60 for these things and I think I spent you know 20 something dollars for this one which I think is actually a decent brand Al Leno LP 560 I don't remember if this is a good brand or not look at sports TTL or Coss it's uh worked pretty well for me in the past but this thing like I said $18 shipped is really inexpensive now I haven't even opened this box it's got a little warranty seal on it I did pay for this myself this is not a sponsored review or anything like that I bought this off of AliExpress and I'm really curious to know like is this thing even useful in the least now the specs on this 200 khz really not not very good what do we really need though to work on a commodor 64 I think that might be fine 800 volts Peak to Peak yeah ignore that that just seems like a complete lie what else do we got here I don't know stuff for more updates on the back here we have some specs 2.5 Mega samples a second 200 khz bandwidth 2.8 in screen 320x 240 which incidentally I have a feeling is the same exact resolution as the screen on on that scope so that's pretty amazing does have an internal battery so this thing does run on battery any nothing much else to see on the box so let's just pop this open let's see what we're dealing with here wow that's really small oh there's our probes wow that's um okay well anyhow there it is it's extremely little a little tilting bail looks like USB type-c that's the single Channel input got a little navigation control there I assume that's a calibration probe or something uh these buttons here are clicky so that's cool and this is the power button I guess and let's just get this off really that failed I guess I'm just going to leave whatever screen protector is on here on here all right let's turn this on hopefully it's got a charge there it is hey it boots up really quickly and it seems like it's updating quickly a couple things I don't know or think this thing has any kind of touchcreen on it so yeah it's not touchcreen even though you might think it is with these buttons down here I think that's just sort of status information it does indicate that it's got a times one or I guess times 10 probe let's see if I can figure out how to do anything on here plug in the probe here has a nice firm connection and I connected the probe up to the outputs on my virtual bench and let's hit Auto I don't really know how to use this thing yet so it's like doesn't even work it's showing some information there I think like it's a 5volt peak to Peak signal so that's correct why don't we see anything on here that I couldn't tell you all right so this little like button on the top here lets me move this bottom thing around does this change oh there we go okay we can do AC coupling DC coupling so that's cool we'll leave it on DC aha the mode button I don't know what happened there but I pushed mode and all of a sudden that appeared on there okay so let's see I want to move that down here so we can see more of the wave form how how do I do that exactly obviously this is time base so that works as expected minimum time base 10 microc seconds all right moving this around I can see here that now that's blue and that's got to be the trigger point I yes and how do I get over to over here to the waveform I guess oh there we go so now I should be able to move the waveform down hey this freaking Works $18 I'm already blown away actually to be honest for the price so let's get this uh looking a little better I mean you saw that it was uh losing the trigger there now I'm sure the trigger is uh pretty poor it's probably a software based trigger we'll just set this up in the middle here but hey we are actually looking right there at one killer and it it's it's working okay so I just held down the mode button and something happened it like made the waveform jump I think it's changing the trigger mode so it's on a downward slope and if we push this now it's on an upward slope so it's got some kind of triggering going on here what if I hold the Run button down oh hey that turns off the measurement all right that's that's something let's see what else we can do can I hold this down no that's just going to change the time base and it just repeats so we'll just put it back to something sensor cold if I hold this down that doesn't seem to do anything at all now unplugging the clip leads I am curious if this has a calibration output right here it does look at that uh how did we get the measurements back there it is 1 khz all right so 3.3 volts that's obviously what this thing runs at inside but look at that it actually has output it's too bad it's not a normal BNC Jack here that so I could use like a regular scope probe instead of being stuck with these s um multimeters maybe there's like an adapter you can buy that goes from this to a standard BNC so then you can use a standard scope probe one thing that's interesting is it's set to run mode but it's almost like in normal trigger mode because it's not triggering right now I guess it only runs in normal trigger mode it does not run in auto mode so if we connect this clip lead back up to here again there it is the waveform is now visible and I'm going to connect it up to the output on the bench scope and there it is it just appeared so yep it's obviously running in normal trigger mode and that means for anyone who's a beginner is it will not show anything on screen until it's actually triggering so make sure you address the trigger point there to like say in the middle like it is right there so that it can actually update the display like it's doing right now so right off the bat clearly this thing is a little bit of a toy but on the other hand it was $18 shipped that's it and this might be actually good enough to try to fix something so I'm going to break out a comer 64 a broken one and let's try to do a repair all right this is the machine we're going to be working on today it says black screen no line well when I write no line that means that when you turn on the computer there's probably no video output at all so typically have the video output on the commor 64 and if the Vic 2 is working but the system is not booting properly because of say some other problem on the computer you're just going to have a solid black screen you have a video signal that's just solid black but you will often or usually see a white line on the left side of the screen and that's just normal for a Vic 2 that's powered up so with this machine right off the bat we can tell a few things by these particular symptoms it we'll need to test again just to make sure that it still has this symptom it other means that well I there's a few things the Vic 2 could be bad the power switch could be bad maybe the whole computer's not turning on the voltage regulator that generates the 12 volts that the Vic 2 on these older bread bin machines needs maybe that thing is blown out maybe it's outputting 18 volts or maybe it's outputting zero volts also the clock generation circuit that generates the clock signal for the Vic 2 which then divides it down and generates the CPU clock and stuff like that if the clock generator is not working at all that means that the Vic 2 doesn't have a clock signal without a clock signal Vic 2 is not going to Output any kind of video signal at the bare minimum the Vic 2 needs to be powered up by that 12 volts or that voltage regulator and 5 volts and also it needs to have a good clock signal going into it now one of the issues is we're going to need to verify that it has a good clock signal but the problem is this cillos scope could do that but little $18 one here which is actually plugged in to charge up there while we're going to look at this Comm 64 it unfortunately will not have the ability to check for a good clock signal and that's because the clock signal that goes into the Vic is around 13 or 14 MHz or is it 17 I think it's 14 MHz on the ntsc 1's and that's obviously going to be way too high but what we can do is use a regular multimeter and even a very inexpensive one usually can measure clock signals of that frequency so we at least can can kind of try to verify the clock signal with that first and then we can kind of go on from there and try to see you know what's happening on this machine but with those things I just outlined we have some ideas of where to start but I think the very first thing I need to do is take this thing apart and let's take a visual inspection inside and just see what exactly is going on I always find it best when doing repairs for machines like this to try to think about like what might be wrong before you even get started just think logically about the problems you're seeing wow that screw was in there pretty tight and uh made a little crack sound so that means this thing probably has not been opened up either ever or in a very long time yeah same thing with that one made a little crack sound and it's very stuck in there wow yeah really made a loud crack sound yeah as I was saying I really just like to try to think logically about what might be wrong with the machine before I even start to work on it it just helps me with that thought process look at the top of this machine someone drew an x on it it's got got a missing key here not the end of the world I think I have some spare keys um H anything else that looks interesting about this computer no not really it's just really dirty and it's probably going to make a crack down when I open it up oh yeah okay so right off the bat a couple things this is one of the uh one of the later bread bins because it's got the the cost reduced clock circuitry here with the what is this an 8501 or whatever I never remember the name of this chip 8701 maybe or 7501 8501 I think that's the one there was a bunch of circuitry that used to be around the Vic 2 and it was simplified down to this 1 I if this chip goes mad well it prevents the entire computer from working whatsoever and it is that clock generator that we're going to have to start with on the diagnosis now a few observations right off the bat we're in good shape in regards to the fact that all of the main ic's here are socketed absolutely excellent it makes troubleshooting much easier especially if you're not good at desoldering IC so if you're a beginner and you open up your 64 and you see this well that's a good thing because you can take chips out pretty easily and uh you don't have to risk damaging your board desoldering things I'm going to try to do as much testing as I can with this little device here and to facilitate that because these probes are pretty sad is I'm just going to take the red probe here and I'm going to literally clip it onto this little pick here and that will allow me to probe around on the motherboard the other clip here it just needs to well this kind of sucks because they are pretty close together here I'm just going to get another clip lead here I'm going to clip onto the RF Shield here just scratch that back and forth make sure it has good contact and then we will put these together here and that will just give me a little extra length I'm just going to push the boots together there so they don't accidentally short on stuff that will give me a little bit of extra length to probe around the board as necessary with this little scope first thing we need to do is we need to check for voltages now what we can do is we can use these voltage Regulators down here and we're going to use this thing here because remember it is showing us the actual voltages because that's the default measurement mode and actually look at this how it's not triggering right now and yet it's running in auto mode so remember there's Auto triggering there's normal triggering which means it only displays a waveform while it's triggering and then there's stop mode well this thing was definitely earlier running in normal mode but now it looks like it's running in auto mode all right so first thing we're going to do is I'm going to move over to there we're going to change this to be something more like 5 volt so when I touch the 12volt pin here this actually you know should go up to around there and we should see 12 volts on there turn the system on and let's test right here that looks like nothing I'm pretty sure I was on the right pin yeah we're getting nothing there and on there we're getting nothing I don't think we're getting any voltage on this thing at all so I'm going to wager the power switch is probably bad here let's poke around on the leads right here just want to make sure I don't short anything out okay so that would be the 5 volts right there uh coming from the power supply it's ending up on the power switch and let's see if it's on either of these leads it's on that lead right now and then the other half of this is used for the 9vs AC so that's not going to be anything right there but the middle pin right there no nothing all right so let's look at the power input in fact I think it should be on the fuse right here oh aha it's only on one side of the fuse I think this fuse is blown well that could indicate a problem uh let's see if we can figure out how to make this thing show us a waveform that looks correct so that is the AC waveform coming in from the power supply it's on this side of the fuse right here but it's not on that side so we can tell right now that this fuse is blown because it's obviously it's on the body of the fuse there and it's not on the body on this side so bad fuse now I could of course just try replacing this fuse but I have a feeling it's just going to blow again because maybe there's something going on with the the bridge rectifier right here like there's a short in it maybe there's a short Beyond here it could be that the regulator itself and this is the 12vt regulator here is shorted now this is a 5vt regulator this is 12 volts and these generate the voltages I think that are used on the Sid and on the Vic 2 and neither of these are going to have any power because this is all powered off this circuit here which includes the fuse now with the multimeter it' be really easy to check that the fuse is bad but really don't need to do that because we know without a doubt that the fuse is blown and it's hard to tell because of the glare from the lights but I think it's that's where the brake is right there I went ahead and I freed the motherboard from the RF shield and from the case because we're going to need to get under here to test this bridge rectifier next to see if that's where the short is so to do that you're going to have to take a multimeter and something with a continuity mode I have my newly replaced EV blog multimeter here so we don't have any problems with the uh continuity mode anymore and let's just flip the motherboard over and you go to where the bridge rectifier is right here I'm going to look for any kind of shorts between these pins now if we uh put the multimeter there we should not have any shorts between these pins nothing is shorted you might hear a beep normally but that that's okay if you reverse the leads yep everything seems fine what we were doing is we just wanted to make sure that there's nothing dead shorted here in the bridge rectifier because if there is that's going to obviously create a short immediately next thing I'm going to look for is any kind of shorts in these voltage Regulators here and that is not a short It beeped but that's fine just want to reverse your leads kind of back and forth just look for dead shorts but that's not a dead short notice the I know it's on the edge here but the resistance was kind of going up there and we're going to do the same over here on the 5 volts nothing just some beeping that's really charging capacitors and stuff like that so you just want to reverse your leads check all the different pins together and everything seems fine okay next up before I pop a new fuse in there is I am going to remove the Vic 2 chip here and I'm also going to remove the Sid chip these are the two chips that rely on the voltages created by these voltage Regulators so I think at this point let's pop a new fuse in there now I have this other motherboard here that I've stolen a few parts off of to do testing and I'm going to do this same thing I'm just going to seal this fuse right off of here eventually I'll replenish the parts on this motherboard to make a working one but for now it's just easier for me to steal stuff from it for testing purposes so there's the fuse all right so I have it connected back up to the RF Shields and look at this if we touch this we get to see some stuff there let's turn this on let's see if we see yep so the fuse has not blown and that's good but we don't have any load on it but one of these chips could be bad that was causing additional load that caused the fuse to blow now the reason why the waveform looks different is because there is now a load put onto the AC input that's coming from the power supply by these two voltage regulators and actually take a look at this that waveform looks terrible this is the 12volt waveform let's look at this one here that's 5 volts 5 volts looks completely fine without any issue at all now of course um this is not going to be the most accurate voltage measure we should use the multimeter on there but this 12 volts looks bad and I have a feeling that's probably because one of these capacitors is no good whoa this one is hot right here it's Mega hot I think we have a bad cap that is a first I mean it's not a first I think I've had this once before but definitely don't usually have bad caps on here it's a 1,000 microfarad at 25 volts so what's happening with AC on the 64s it comes through the the power connector goes through the switch goes through the fuse or I don't know might be going through the fuse first and then the switch can't remember which way it is then it goes through the bridge rectifier then it goes through one of these capacitors here and I think this one here is handling the um rectified 9 volts and yeah that's still really hot and then it goes into the voltage regulator and then out should come a nice clean 12vt and I think what you should have here is like 15 volts or something like that I don't really remember exactly but clearly when a cap gets super hot it's not working properly anymore so I'm just going to snip the legs of this cap we're going to reuse uh those top legs cuz I don't have an axial cap here to put in its place now I'm going to use this LCR meter which is kind of a fancy device for testing capacitors to test this capacitor well it's showing 423 microfarad but this is actually a 1,000 microfarad cap but strangely it shows an ESR of only .81 now it's running at 1 khz there let's change this down to 100 Hertz 1.4 ohms 883 microfarads I mean I don't know if that's necessarily bad looking but clearly there's something wrong with this cap because it shouldn't get super hot there must be some serious leakage or something else going on with this so it doesn't even really look bad on here but clearly this is bad okay went into my little Parts spin I found this 1,000 microfarad 25 volt nichon and remember oops this is uh exactly what I just took off the board and clipping this onto the ESR meter here all right well there we go 0.01 ohms 955 microfarads and 100 Hertz so yeah I guess that looks better the other one I think what were we getting a higher reading on here but not we weren't getting like 30 ohms or something like that we were still getting a relatively low reading so who knows anyways this cap should be fine problem is this was pulled off of some other board so it has super short lead so I'm going to have to kind of bodge that onto there all right so there we go the random capacitor is connected up and I just used this off cut of wire it's all pretty ugly and it's sort of flopping around in the breeze But ultimately don't be afraid to use spare parts you have lying around just like this and all I need to do to kind of secure this just use a little bit of hot glue on the motherboard to connect this uh capacitor down so it doesn't just flop around and even though this is super ugly this should absolutely work properly so let's take a look now at the 12vt put on this when we power this thing on first of all is this cap getting hot no it is not so now when we look there take a look at that we are seeing a really good clean 12volt output now and looks like it's uh it's running a little bit High 12.6 let's take a look at it with the multimeter I don't really trust this thing to be very accurate when it comes to measuring voltages and I'd say it's good to make sure the voltage you're about to put into your vic2 chip is actually pretty good ah that is a bit High there look at that 12.8 I don't trust that I think that's high because it probably was potentially getting damaged by the excessive Ripple that was coming through that bad capacitor I removed and it's the next day I have to take a little bit of a break let's get back to testing this little miniscope and see if I can get this Commodore 64 working after I stopped recording yesterday what I ended up doing is I ended up swapping out the bad 6812 voltage regulator so here is the bad one that came from the motherboard there's the bad fuse there's the bad capacitor we found I also used this eraser pencil thing that a viewer sent in and I cleaned up the contacts here on the user and CET Port you may have noticed I didn't really point it out but these were looking pretty crusty and uh well this little thing made really quick work of it I think any kind of pencil eraser would work well but this one is just extra convenient because it's in a little pencil shape you may noticing as well the motherboard looks a little bit cleaner and that's because I gave it a quick wash it was so dirty everything that was touching it including like the mini scope here sitting on top of the RF modulator was just getting filthy so yeah I gave it a clean and it's had all night to dry I added a little bit of hot glue as well to hold down my little horror of a capacitor replacement and I just want to mention again that yes I could have used a proper axial cap to do the replacement I don't keep any in stock or even I could have used a new radio cap with longer lead so it wouldn't have had this whole wire but I really just wanted to show that you can use stuff you have lying around to fix stuff and yeah it doesn't look perfect but this computer when it's done is going to be back together in its case and no one's ever going to see that it has that kind of ugly mod and if anyone ever put this in a clear case and wanted it to look perfect well you could just go ahead and replace that capacitor and that wire I'm approaching this particular repair as something that you can do very inexpensively which is why I'm going to try to use this $18 scope as much as possible all right enough talking let's get back to troubleshooting all right let's turn this thing back on now what I haven't done um there we go it's booted up what I haven't done is tested out the voltage here that's coming out of this regulator post replacement look at that that looks perfect no more Ripple but also well of course no more Ripple because we fixed the capacitor problem but also notice we don't have that high voltage anymore it's obviously just slightly below 12 volts now which is perfect let's just double check the output of the 5volt rail and I'm going to say that that looks good as well I just Chang this over to 1vt per division so when we touch the 5 volts here we're going to have more resolution so to speak the more appropriately set the per division voltage rating is means that it's going to have a bit more accuracy on the measurements here and now you can see that we're actually much closer to 5 volts in fact we're pretty much just exactly at 5 volts now which is basically perfect okay so the power side of this machine is completely working perfectly now it's time to put this Vic 2 back in here and let's hope that it didn't get damaged I mean the 13 volts this was outputting was fine but that Ripple wasn't a good thing either so hopefully this thing is fine it probably is going to be fine I'm just going to give these chips a little bit of a push here there we go okay I'm going to leave the Sid out we don't need the Sid for operation of this machine few things I've noticed by the way uh there are some Moss ic's here so those are those are problematic the ram is Fujitsu though which is generally reliable it's not like mt Ram nothing specifically bad about it and of course finally the Moss pla that's in here is very suspicious these things well you can always suspect they're bad and it's very nice that it's in a socket for the next phase of this repair I need to look at the schematics but one of the issues is my setup here I don't really I'm not set up for using these types of things where I'm not looking at the osilloscope on the desktop of my computer which means it's kind of hard for you to see what I'm doing and to see the output of the scope so I think I'm going to just try to position this close to what I'm testing and hope the glare is not too bad and yeah like that all right so the first thing we want to look at when we turn this computer on is we want to see if there looks to be a good video signal that's a really good way to know if your monitor or your capture device is working correctly because occasionally like you plug in something a retro tank or some other scan converter and it may not be working or maybe whatever monitor using doesn't like the comer 64's video signal so using a scope like this even something cheap like this we should be able to see a video signal and that is on pin 15 right here of the Vic 2 this thing is outputting some kind of video signal so I'm going to use this little pointing device here so that is the white line on the left side of the picture so this is one scan line and this is the horizontal SN pulse so right here is where the beam on the CRT goes back to the left side and then it scans across the screen and if we had content there for instance blue Borders or text you would see stuff in there and we're not we are just seeing always the same thing here which is absolutely without a doubt a black screen this is pretty cool there are a lot of limitations on on this particular device but it is still good enough for us to see that there's a video signal and we've confirmed without plugging this machine into anything that we absolutely do have a black screen this is something you could not do with a multimeter or with a logic probe now zooming into the Vic 2 here this right here pin 17 is five out or 5 Z out that is the clock signal that goes to the CPU should be around 1 MHz it's pin 17 let's take a look at what that looks like I don't think we're going to be able to see anything with this device but we should see something all right well I mean that's something right there so going down to 10 Micro seconds per division that is the lowest we can go to and you know unfortunately I think what we're really looking at there is just aliasing this thing is just not fast enough to show us a 1 mahz frequency now we knew that of course this thing's only rated for 200 khz it does show us that there's a signal though if this were stuck at zero or 5 volts then we know that there's something wrong and there's no way the CPU is going to run but that is showing us something is there now just for fun let's just poke around on some of the other pins on the Vic 2 here so starting on pin one right here I mean we have something going on there now pin one is looks like data line six which you know I have to say looks very suspiciously bad actually that does not look correct pin two is data line five I mean that looks like more like a data line what I would expect it to look like remember at 1vt per division so 5 volts should be up there that is pin three data line four and I'm on pin seven here which is data line zero and again that looks m a little weird I'm just going to power cycle the computer here use my left hand to do it yeah now it looks fine look at that so it was weird looking and then now it looks the same as the rest let's check out that pin one again now the problem is here is there could be some activity that's just happening more quickly than this scope can resolve and we're just looking some aliasing there so that might not really be a problem actually it's hard to know having not used this thing on a real working machine it's not going to be easy to tell now where this thing should be useful is on the output of the pla here which incidentally is quite warm I have it up on my screen I know you can't see what I'm looking at but I'm going to be looking at the output lines these are the chip select lines that come from the pla that go to various things on the computer all right so let's start on pin 10 on the pla here this is ROM h I think ROM high for the cartridge slot so that's fine as long as it's not stuck low then we go on to pin 11 ROM low same thing looks totally fine pin 12 this is the io line and let's power cycle the computer here oh I was touching the uh metal thing here look what happens it picks up the lights around me so make sure I don't do that that looks fine as well it's not stuck low pin 13 is the grw line I think this goes to the color Ram so that's fine it's not selected right now next up is the character ROM selection and we can see little spikes happening there but it doesn't look like it's stuck low and that's what I'm really worried about now no characters are being drawn to screen so really there shouldn't be anything selecting that ROM at this time the next one is the kernel ROM pin 16 it's not really being selected either then we have the basic ROM same thing not being selected at all and then we have the C Ram line now unfortunately I think this line is running at speed Beyond beyond the capabilities of this little oscilloscope this is where we're going to run into limitations of this thing it's just not going to be able to resolve that signal it can't go any faster than that and this is exactly what I'm talking about I'm on the same pin but I'm using this little uh zoy now and it says it's running at 2 MHz this is the same Cas Ram line yeah there's just no way this can be resolved on that other little scope now this signal looks fine it's not triggering properly but that's fine it's just uh the trigger point is in the wrong spot there we go now it's in the right spot and yeah I mean that's the difference between something that actually is able to resolve multiples of megahertz versus something that's not all the other lines though that we've already looked at they look fine on this scope just like they did on the other one now the funny thing is because we're not seeing any kind of weird problems with the pla on this machine actually looks like it's operating normally let's go look at these data lines again the ones that looked funny on the other one aha so this looks like normal activity actually what looked problematic activity on the other one looks fine on here now if we zoom out a little bit yeah there we go so we have kind of normal activity on the data line now all this extra overshoot just because I'm using this uh screwdriver as a probe is actually okay so looking at each of these lines it looks okay taking a look at the clock signal which we couldn't really resolve on the other one there it is 1.02 MHz so we know that is perfect and this is the video signal which we were looking at on the other one if we zoom out here we get much clearer view of the video signal the sink pulses and then we have the white line and there's definitely nothing on screen this computer is for sure not running now one thing about this machine is it has been turned on now for several minutes and what I want to do is I'm first going to look for any chips that are super duper hot uh the CPU is is very very hot that's that's a suspect chip right there it's much hotter than I feel that that should be pla is warm but nothing nothing extraordinarily hot Vic 2 is very hot but that's that's par for the course let's check out these ic's here so feel around for the RAM chips you don't need to use a thermal camera for this you just need to use your senses so far so good nothing is burning hot a bad Ram chip can often manifest itself as like a burning hot chip so you have like one that's bad yeah this stuff all feels fine now I'm used to 64s if you're fixing one for the first time you're not going to know what what's hot and what's not Sid chips get hot Vic 2s get very hot pla's get pretty warm ROM chips get warmish the 6526 is kind of warm CPU though it's really it's super hot right in the middle where the die is I think what I want to do next is let's take a look at the address lines we need to make sure that this is addressing the ROMs correctly because the system is not going to boot at all if the CPU or say has or say one of the address lines maybe du to mother chip to be honest has an issue so we got a let's look at the address bus we looked at the data bus already we looked at it on this which wasn't super conclusive we looked at it on the other zoi that was definitely more conclusive but address lines are definitely the next thing we need to look at when the 6502 or 6510 in this case initializes it tries to jump to a reset Vector which is like FFF a b it's right at the top of memory space so the very first thing this thing should do is set up the address bus as such it's going to start booting from the kernel ROM the pla Maps the kernel ROM into that address space that top of the memory and that's what the CPU needs to do when we turn it on we're going to start on pin seven on the CPU which is address line zero I'm going to turn on the machine here okay it has lots of activity not necessarily a bad thing and I'm just going to go down the line here and look at all of the address lines just looking for anything that's like kind of out of the ordinary you know we see normal activity going on here which is okay goes all the way up by the way to pin 23 so I'm looking for anything that's like you know two volts or say it's just stuck at zero volts all the time I mean being stuck at 5 volts like that not the end of the world it's just power SL in the computer there oops so there's some activity we're not able to really resolve it because this thing just has limitations obviously 19 pin 20 wow those are just stuck I don't believe those those look wrong to me see how this is just really held hard up against five volts but this address line has activity and when I turn it off and back on you know we see some differences there but these two lines look at this that's just that's like a dead short so pin 22 which is address line 14 looks like a dead short and the same thing goes for this next one here pin 23 address line 15 abs abolute dead short all right so there's a couple things we can do we can pop the CPU out with the CPU removed from the system those pins should not be a dead short anymore they should be just kind of floating so let's turn this back on here and let's take a look okay looks like a dead short still and same with that one let's power this thing off and on yep that does not seem right let's go over to one of these pins that was not like that and there is activity on them H so when talking about address lines on the c64 the higher address lines which are the ones that look like they're dead shorted they don't go to that many things they don't go to the ROM sockets for instance so it's not the ROM that's doing that oh and you know what take a look at this they're actually pulled right up to 5 volts through a resistor pack I'm pretty sure it was actually these four lines that we saw that were held up there at 5 Vols okay so that means that that dead short that it looked like was by Design cuz it has those those four lines pulled up now my problem is if this CPU were working even if there was like a dead chip like the kernel ROM or bad I have a feeling we would see more activity on those lines than we are now we're just seeing absolutely nothing happening at all and if you're asking the question why are we seeing activity on the address lines with the CPU removed that is because the Vic 2 if it's working is sitting there trying to refresh its screen and it's trying to read from screen memory to do that and to do that that means the Vic 2 is actually accessing the dam and the color RAM on the machine even without the CPU in here and if I recall correctly the aec line which is the output on the Vic 2 is what tells the CPU hey release the address lines and let me drive the address bus and it comes into the CPU right here on pin five we should take a look at Pin five even with the CPU removed and we just need to see that line I think should be toggling and indeed right there we see there is activity on it although it's you know we can't really see it clearly I'm pretty sure what happens is when this line is asserted the CPU goes into halt mode and disconnects itself from the address bus and the data bus actually for that matter and then it sits there and it waits if this line here on the scope were just stuck low or high all the time that would be a problem actually but the fact is there's some type of signal line here that is not low which definitely indicates that I think the CPU should be able to execute in between these pul PES so I have my parts board the one that I stole the fuse off of I'm just going to steal the CPU off this now I don't actually know if the CPU is working on here but we'll just have to make an assumption that it is and just so I don't mix these up the one I just took out of the parts board has a yellow dot on it already something that I didn't do and this is the one in my right hand is the potentially bad one so we'll just pop this in here the machine is turned off right now and one way to know the system is actually executing any code is to look at the chip sleck line that goes to the kernel ROM from the pla it's pin 16 on there and let's turn this on now and see if we have any activity oh we do indeed so that is something we did not have before with that other CPU installed that implies that this system right now is actually trying to execute now this CPU isn't even warm at all why don't we take a look at the video signal on this little scope here whoops that is pin 15 here 15 there it is okay well we can tell right off the bat at the video signal that we have a border I don't know if we have anything on screen a text oh yeah there was did you see that oh this thing is working whoops I fell off the pin so what we're looking at here is the video signal I'm just trying to make it so it's not glary here and you see how occasionally there's stuff there that is freaking text on screen so that is the border the lighter border and then the darker background and then the the bumps we see there is the text so without a doubt I don't know if this thing's working perfectly but it is not a black screen anymore and it is showing text on screen now and we have borders and stuff like that we have a big Improvement if I power cycle it you'll see the black screen for a little while with the white line and then it will display the Border watch there it is Boom there it is there's the border so right there this thing's good enough for us to tell that we have a good video signal let's hook up the uh capture device okay there's the Retro ttin I have it set for composite let's power this on let's see what happens come on ah look at that it freaking works I knew it you know we could tell that it was outputting text because we could see it on the mini scope here and it's working it's freaking working how awesome is that all right Sid chip is in there let's get something hooked up to the audio here so we can hear the Glorious Sid sounds let's put in the diagnostic cartridge first you know I didn't we should actually try that right so here's the diagnostic cartridge see this if this works could be still a problem with the pla oh no look it's actually running now unfortunately I don't have my test harness for connecting to this thing for final testing and that's because I lent it to someone who needed a test several machines so for now we're just going to have to use diagnostic ROM without the harness which will give a bunch of errors here but we should be able to hear the Sid working and then we'll try out the uh good old you know what I won't say the words but I think everyone thinking it ah there it is so Sid is working cool while the diagnostic is running what I wanted to do is probe around on a couple data lines and address lines and things like that so we can kind of see how it looks on this thing while the system is operating normally so I'm on the Kernel ROM on pin 9 which is data line zero and while we can't get a good view of what's actually happening on this line we do know that it's not stuck at 5 volts or stuck at ground it looks I'm going to call this normal it'd be nice if this had higher resolution so we could resolve more stuff than we're seeing there it looks almost like noise but that's what happens when you look at a signal that's too fast for an oscilloscope on something that's running too slowly and here we are on address line zero and also that just looks kind of like noise because there's a ton of activity on that particular line and it's just not able to resolve it and here we are on a higher address line and again we just really can't get a good view to see if this is bad or good but what I can see even though I can't clearly look at the line you can see that it's being driven correctly up to 5 volts well or high signal which is like 4 volts is in this case or all the way down to ground and that tells us that this particular address line is actually fine there's nothing wrong with it and moving on to the next one same thing so you can see that there's bursts that go down to zero and then bursts that go up high there's a lot of stuff in the middle there which you know I don't know we can't really tell what what's happening on this thing but it's giv that's an idea that that line is actually good incidentally I looked in the manual and by the way it goes over the short and the long pushes on this particular thing it tells you all the various differences there's some kind of automatic calibration junk you know I didn't even bother with that stuff but it looks like here it does say Auto single or normal switch setting so you can do single shot mode by pushing a short press there that's kind of cool and then we already figured out here the rising or falling Edge for the triggering and then it's the Run button the short press which will run or pause the waveform and then we figured out that long pushing it will open and close the measurements and this thing does support a 10x probe you're going to need to use some kind of adapter because clearly uh you're not plugging a normal 10x probe into this little funny little Jack on here I looked online I did see them selling adapters but uh when you get the adapter plus a probe it ends up adding another $8 or $10 to the price of this thing and then you're at like $30 and I'm not quite sure it's it's worth it at that point for the very rudimentary stuff we're doing here frankly using the clip leads and that little uh pointy thing is well it's been good enough right all right so let's pop in the easy flash here this thing is a tricky cartridge to run so if it doesn't work then there's obviously more things wrong with this computer so let's power on the machine hey look at that it did come up and good I can go to adrianne's tools that was my fault there are adrien's tools and let's run the aid dance party I have the sound turned [Music] down okay well anyhow that sounded perfectly good I'm going to say that this machine is fully fixed I won't know 100% for sure until I can use the test harness on it but obviously we have good Sid sound the CPU is running now it's working well all right so there we go the question of can I fix a comer 64 with this mini oscilloscope I'm going to say resoundingly yes is it ideal no not really would I recommend you get one of these well if you don't have any oscilloscope at all and you don't really even want to spend like $80 on something like this or even I think it was like $57 for the cheaper one Channel version which also has a smaller screen and lower bandwidth well then yeah I mean this is absolutely 100% without a doubt better than having no oscilloscope at all because as you saw we were able to validate that the power rails look good we were able to find that bad capacitor we were able to see that the video signal was good on this thing and we were getting a black screen and then we were also able to validate those upper address lines were stuck at 5 volts which really implied that the CPU was not trying to drive them and of course the CPU being burning hot was also was kind of a Smoking Gun for a problem with that ship and then once I swapped out that ship I was able to see on this before we even plugged this into any video device that we had a working video signal with the borders and text and everything and that is all something you just cannot do with a regular multimeter or a logic pro so for 18 bucks if you have nothing and you don't really even want to spend the money on something like this because you're just such a casual user then yeah this thing's pretty good now I think it was on sale when I got it for $18 If This Were say $35 I would have a harder time justifying it I know the increase from $35 if that's the regular price of this for instance all the way up to 56 for the cheaper version of this is not nothing that's not like that's no money but the thing is this truly is a decent piece of test equipment it's not great I don't love this by any means but as you saw when we did a comparison we were able to resolve signals very clearly on this when this thing was just unable to resolve those we could tell there was a signal there it just wasn't showing us any detail it wasn't able to count the frequency or anything like that not to mention this zo thing is actually a a multimeter as well it's not a good one but it's a it is one so if you don't even have a multimeter then you're going to getting two for one with this so yeah the one Channel version of this probably better than this but again $18 less than I paid for my lunch yesterday this thing does work it really does what it says it can do I don't feel the specs that this thing says it is 200 khz is even a lie it's it seems truthful to me and in all honesty it's quite amazing we live in a time where you can go out and buy something so cheap that's actually seemingly well built like this doesn't feel cheap and crappy and yet it does freaking work and I was able to fix this commoner 64 with this of course a bunch of knowledge I have on fixing them but nonetheless I feel that I was able to see stuff with this and I hope I showed that in this video that really did Aid me in fixing this and I would have had a lot harder time fixing this board if all I was armed with was a multimeter and a logic probe or even just a multimeter yeah this absolutely did help in the case of this and really I cannot recommend enough if you're working on repairing anything and you want to go beyond just part swapping like Parts scanning chip swapping recapping that kind of stuff having an oscilloscope is an absolute essential tool so anyways I think that's going to be it I'll put a link to this thing down in the description below like I said I paid for this and uh I don't get anything out of you buying them there are lots of other reviews of this zo one out there so uh just type in zo um oscilloscope if you're trying to find a review of that I really want to thank my patrons for all the support I get here and the channel it makes it possible that I do this full-time their names are SW off the side of the screen over here if you want to become a patreon you can do so there's link description below all that stuff like that uh they get behind the scenes things and whatever all sorts of good stuff like that and I think that's going to be that if you enjoyed this video I'd really appreciate a thumbs up check out my other videos second Channel all that good stuff and I guess that's going to be that so stay healthy stay safe I'll see you next time [Music] bye-bye

Channel: Adrian's Digital Basement

Views: 261,345

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Id: iG0-0R9qYWU

Length: 51min 29sec (3089 seconds)

Published: Sat Mar 23 2024