Fixing two C64 motherboards with hot chips

well hello everyone and welcome back to adrian's digital basement on today's video is something i haven't done in a little while we're going to repair some commodore 64s so without further ado let's get right to it [Music] all right so this is not a 64 here that needs any repair this is my good old zif64 and wow the bottom of the keyboard sure gets warm from these ics in here when you have the cover on even when you have heat sinks it overall is really hot the reason why i had the zip 64 on the bench is to double check that the power supply is good and my capture setup because i've been having a lot of problems with the capture but with my new dell t 1700 desktop i'm able to successfully capture video once again all right for troubleshooting today we're going to be using the double ended dead test slash diagnostic cartridge and yeah i had to dremel away the case because i ended up needing to replace the eeprom and the only way you can put this case back together with the ebroms in is if they're soldered directly onto the pcb we'll be using the virtual bench so i have the oscilloscope probe right here and we'll be using the easy flash as well if i get the system working and we need to run some dance party maneuvers all right here is the first motherboard we're gonna be looking at today i actually don't know how many we're gonna be looking at it's gonna depend on how much work they are to fix obviously here we have a short board and i wrote bad ram with a question mark this would be a fully populated ntsc short board this is from later 64cs of course and it came from michael orange which is one of my viewers this was sent in for a mini mail call or a regular mail call i don't remember so on this version of the 64 there are two ram chips and the one on the left here i put a little mark on there it's one of my question marks most likely because when i power this up and i'll power it up right now i think what i found is that chip was getting really hot very quickly so let's let this run for a moment here it would definitely be causing a black screen if that's the case um okay let's see here just use your fingers yep okay this ram chip is fine these other chips around are fine but that one very warm okay so first thing we're gonna do is we're just gonna pull that out of the board there would be no circumstance no matter what's going on on this board that would cause one of the two ram chips to be that hot now that we flip this board over there's some tell-tale signs that both of these ram chips have actually been swapped out at some point see that a little bit of flux residue that's here on both of them that would definitely not be there if these were the original factory installed chips i gotta say i find that kind of rude if someone did swap these out that they didn't install sockets because this would have been like a two minute fix if that was the case and actually check it out 1987 date codes on the ram chips while all the other chips in this machine are 1989 so that's when this computer was built at the factory and yet someone installed these older ram chips that in and of itself is not a problem it's just the fact that they didn't even bother with the sockets [Laughter] okay the bad chip has been replaced by a socket let's just grab one of my tested chips that i know work i'll stick that in here boom and hit the power boom there it is working why don't we go right for the 8-bit dance part here power that on look at that nice clear image i plugged in the zip 64 keyboard and here we go 8-bit dance party oh that was an anti-climactic i have the speaker turned down [Music] [Music] okay so obviously things are working at least they're able to run this demo here the sid on this thing of course works well because the sids on this generation of 64 are very reliable i've said that many times on the channel the thing is they sound a little weird and you might notice on the music there i had been doing an audio capture the bass line is a bit strange and that's not a fault that's just because the sid is quite different than the one from the old machines the 65 81 so it just goes with the territory but this particular sid is in more of these 64 cs i'm going to say out there in the world there are more 64cs that probably work especially over in europe where they were selling these machines a lot more than they were in the u.s so i think a lot of modern games and demos are actually designed with the sound of this sid in mind and not so much the old one but you know obviously it's compatible they're both compatible with the same software they're not interchangeable between the machines though but the sound is a little bit different okay it's time to break out sven peterson's diagnostic harness here let's uh pull out the easy flash we're going to be popping in the regular diagnostic cartridge here now let me mention that if you are repairing your own 64 you don't need the diagnostic harness like this this is really for someone like me who tests a lot of 64s you can of course test the ports on your 64 by just using them plug in a joystick plug in a disk drive plug in a tape drive just use those things and if they're working and your 64 seems to work properly then there you go this is really just a very fast way to double check that these ports all work all right let's power this up hmm oh i have dead test plugged in that is the problem i have to reverse this thing diagnostic cartridge is that way powered up there we go okay that flash had nothing to do with the the 64. that is the video capture stuff it's a little flaky sometimes all right looks like everything is working and then we already know that the sound test is working fine because we heard the music in the uh intro there it sounded perfect so if you run this diagnostic cartridge on your 64. i think i pointed this out before but if you're new to 6064 without the harness you're going to have a bunch of things that say that there's a problem don't worry about that that doesn't actually mean there's a fault just simply that the cart harness is not plugged in one little tidbit that you may not know is down at the bottom you'll notice there's two clocks one says 1 10 am one says 1 10 pm well the time keeps advancing those are clocks that are maintained inside the two 65 26 chips on the 64. they're the i o chips one is for user port one's for the keyboard and they do a few other things as well those internal timers just show that the time counting is actually working and the chip is working if the chip is totally dead or it's removed from your system you're going to get garbage instead of a correct time there you're just going to have like a bunch of random letters and numbers and it won't count down so it's a really quick and easy way to know if one of your 65 26 is as bad on your 64 without having the diagnostic harness so as we can see it's already ran through multiple passes and everything is working so this 64 is completely functional now all that was wrong was that bad ram chip now i haven't repaired a whole lot of these short boards before because they're very reliable but if you're going to have a problem on your shortboard let me just tell you what i think are the most common issues definitely i've had more than one of these where the ram chips were bad they're not always hot to the touch like this one was when you power it up so don't rely on that but if you feel one or both that are really hot that means there's a fault these chips don't get warm even after extended use of the machine the other most common failure on this type of board though that will result in a black screen is actually this chip here the 8701 this is a clock synthesizer chip which basically helps the vic 2 chip generate the clock signals used on the 64. without that chip in there or if this chip is bad you're going to have a machine that doesn't work at all luckily there are modern replacements for this you can buy them from various places here in the u.s jeff burt sells them i'm think but just look online for 8701 replacement and you can find that if you had an oscilloscope handy you could actually check the clock lines on this and see that it wasn't generating clocks or they were not looking right and that could help you figure out that that's the bad chip a logic probe might also be able to do it but because that can't really tell you if the clock signal is wrong like the wrong speed or it's glitchy or whatever it's not ideal an oscilloscope is gonna be your best bet for figuring that out luckily i've only always seen this chip here in a socket so it is easy to swap out if you're not really sure if that's the problem but unfortunately the ram on these boards is always soldered in unless someone's already replaced it and installed a socket so you're going to have to remove the old chip which is dangerous because you could lift traces i'm not sure why i didn't demonstrate this but i should have used some cutters like this to just cut all the legs so you remove the black plastic package and you're just left with the legs in the board and then you just take your soldering iron and you heat up each one and use tweezers and you pull them out of your board gently that is the safest way to remove a chip from a board even safer than what i was doing using the hakko desoldering iron anyhow michael orange thank you very much for sending this in i'm just going to put that there and put fixed maybe i'll put the date here i'll just put 12 20 21. and yeah it was the bad ram u10 that was it the only fault all right here is our next victim or sorry next machine we're going to be trying to fix uh it says dc that must have been the viewer i think who donated it but i don't remember your name but i wrote black screen with the and then with the dead test sometimes flashes corrupt test screen loads of moss chips and i'm talking specifically about the ttl logic that commodore used to replace the chips when they couldn't get like a 74 ls whatever they made a version of themselves and they are super bad quality and i put hot u14 that's probably one of those moss chips so we can definitely suspect that there's going to be some bad moss logic chips on here so let me uh open this thing up so this one just like the last one has the 8701 and that can fail and of course cause a complete black screen the pla of course can fail and cause a black screen although take a look at that this one has a pls-100 so this is a pla that is very much like the 82 s100 that was first put into this machine this is not made by commodore and i think these are very very reliable so it's very unlikely that this is actually a problem it seems like this motherboard is a little bit of a part special because that pla is from 1987 and this could have been a replacement that someone installed 1985 20th week 1983 16th week then we have 84 84 84 24th week then we have one of the 65 26s from the end of 84 another one from the middle of 85. the fact that these are all socketed you never know someone might have been swapping parts around and we look at the ram and the other soldered ics here they're all from around middle of the year 1984. so that's probably when this machine was actually made and so i think it's unlikely that things from 1985 were in here originally these were probably installed after the fact notice the ram is all motorola branded except for this one i see here that's almost certainly factory commodore did stuff like that they just used whatever they had on hand probably was like a big bin of ram chips and just grab them and stick them in and i guess there was just one of these parts mixed in with these other motorolas and you're just going to see lots of random stuff on these boards these are the moss chips i was talking about that often fail these are normally 74 ls something or others and these are the cheap crappy moss versions of them and then this is one as well and then this chip here is in the socket we'll have to look on the underside to see if that is original but uh it's from 1983 which is before this machine was even made so it's kind of unlikely although commodore was known to put sockets on boards too and then whenever they had the chip in stock they'd actually install it so that was their their way of getting machines mostly built and then they could finish building them by putting the chips in that were still empty on the sockets all right so next step get this thing out of the case so we can take a look at the underside this does have an rf shield that is soldered onto it looks like this plastic standoff broke on the case it did indeed it's missing entirely from there so it's stuck on the bottom that's what happens uh if you have this happen jeff burt has a little kit you can buy he has new standoffs you can buy and you glue them onto your case and yeah you can repair that stuff for removing the rf shield that's on the bottom of this thing one way you can do it really easily is you just use some cutters again like these and you just snip it off around the edges i know people hate it when i do that the thing is there's a lot of thermal mass between the ground plane on the motherboard and the shield itself so you have to use a soldering iron that is able to actually quickly melt and take care of the solder so if you want to take it off though you just melt the solder that's on there with something with high thermal mass and then use like a pick or whatever like i have here to just scrape or lift it off there we go and bend that out of the way please keep in mind that in the us this rf shield was installed on all 64's but in other parts of the world it wasn't so it's really has no bearing on the actual functionality of the 64. it was purely for fcc regulations in the u.s specifically and maybe some other countries that required the installation of it but plenty of this exact motherboard design in other parts of the world wouldn't have it at all so if you take it off you're not going to impact the capability or the functionality of your 64 or the reliability of course you'll make some people mad because they feel like it should be there and et cetera et cetera but ultimately in this day and age we have so many things that cause interference like led light bulbs and stuff like that that your 64 that you turn on occasionally it's just not going to make much difference to the overall rf noise spectrum this is in 1983 or 84 where we didn't have like everything under the sun with a switching power supply all right so that is off there there it is now there's still okay i was gonna say it was still connected right here in between the ports but i couldn't reach there with the desoldering iron so that is off okay so that goes bye-bye all right now that we have the bottom exposed let's take a look what's been worked on on this machine all right right off the bat this right here has been replaced which is this chip here in the socket so someone took that out whatever went bad and put a socket in so thank you very much for that i'm going to say that nothing else has been worked on at all on this machine and by the way i just want to mention something that i think some people have pointed out before in comments see this wrinkled appearance to the traces that are on this thing that's not a failure or a fault in any way like that's the way this has been since it was made back in the old days the manufacturing techniques for large pcbs just wasn't the same as what we have today and certain companies when they manufacture the 64 pcb you got this sort of wrinkled effect and it's been like that its entire life so don't think that your board is like falling apart because you see this wrinkle stuff going on it's been like that since it was made and it's completely normal now it's interesting it's not on the top at all and it's only on the bottom and i think the the engineering nerds from the old time can probably explain why it's usually on the bottom more than on the top but i do know for sure that it's not a sign that this board is dying or anything it just means that it was just made that way this particular one was made in hong kong it says made in hong kong there as well who knows that maybe that plant always made wrinkly traces there's some wrinkling going on the top here as well like here and around the vic chip but like i said totally normal and not a problem so this particular revision of the 64 motherboard is right here 250 425 and a quick google and it brought me to this page here and it's an 8 pin board that means the video port has 8 pins and it has the oscillator chip or the 8701 that's this here so instead of the circuitry that used to be on the 64 to support the oscillator it now just has that one chip which is driven by the crystal oscillator i have a mark on this ic here which is u14 it's silkscreened on there and we look here u14 is a 74 ls 258 multiplexer so it has to do with the ram access i think and there it is there's that multiplexer so it's hooked up to various address lines on the machine specifically for the looks like uh down through this latch to the character generator rom and also to the vic 2 here so we're going to get all sorts of issues if this thing is not working properly okay so the oscilloscope is ready and the machine is powered on i'm just going to quickly go through all these pins and look for anything that looks out of the ordinary like for instance voltage levels that are out of kilter like they're in the middle somewhere so far these all look fine okay that looks wrong so we're gonna keep going for a sec okay this is all fine the one that looked bad was pin four okay [Music] good yep that's fine that's not doing anything oh there we go i just didn't have good contact on it okay that's good yep that's fine and that's that's gonna be uh voltage okay so this pin right here is pin four alright so i'm on pin four here that doesn't look right and that is also connected right here to this ic which is u13 which surprise surprise is another moss i see it's this one right here and i'm pretty sure that this ic that's been replaced is also the same ic part as that which is uh 74 ls 257 these are both 257s and you know what that chip is not that hot but that one is let's check the outputs of this so pin 4 which we already know is bad 9 7 and 12. it's really burning my finger touching it there all right so 1 2 3 4 so we know that's that's going to be not looking good five six seven there are seven um that's not right look at it it's all high that's really not right at all it's all way up there nine okay nine doesn't seem super bad 10 11 12. okay 12 looks fine okay so two lines on there look really bad i'm going to turn the computer off it's obviously causing a bus conflict or something so we're gonna pull that out the fact that it's really hot dead giveaway there's a problem that's is you know shorting these two chips together there they're both trying to drive it at the same time probably and that's causing a problem so i'm going to mark the board right there and we're going to take that out oh look at that i didn't even have to use hot air to get this chip out that just came right out nice all right socket is installed 74 ls257 let me find one of those okay i found this in my part 74 ls257 from 1979 nice and old because it was in my parts span and completely untested i am gonna do a quick test of it first on the uh chip tester pro here the pins on this ic are extremely mangled don't know where i got this from definitely pulled out of some piece of equipment and yes you may be noticing that this thing looks extremely good now and that's because this is an oled screen that was donated by a viewer for the chip tester and look how amazing that looks anyhow 74 257 there it is let's run the test oh this may not be in the socket all the way though but this also could be a bad chip that was removed out of uh something oh no there we go it's good it was just not in there all the way the pins are really dirty on this so anyways we know it works i mean we can test this moss one just for fun i guarantee you it's gonna fail right there chip failed in fact let's just move that around in there try that again 257 right there dead all right so let's install this new part while new old part into the board here now there may be other faults on here right i mean there's all these other moss ics they're so flaky so turn the power off let's plug this in let's switch back to hdmi and power this on what are we going to get uh oh why are we not seeing anything how about because i don't have the cable plugged in oh look at that it's working that was it that was it why did i write u14 on here hot u14 when u13 was clearly the problem after poking around with the oscilloscope okay should we just jump right to this or should we try the the diagnostic cartridge why don't we just go right to a dance party all right keyboard is connected make sure the speakers turned up uh the little this this cable does not work very well i have to say all right it's pretty noisy sid chip in this machine [Music] we have a bad sid chip let me do a direct capture so you can hear that [Music] do [Music] all right well it's weird because it sounds pretty normal there in that part but i'm gonna go back to direct capture here and then we'll start again so you can hear the intro to the song which sounds really screwy [Music] [Applause] [Music] i'm going to say that all the voices are working but some of the modifiers or whatever the things that change the way the voices sound the filters that's what they're called filters is not working correctly so when it uses those particular filters that channel is really quiet and muffled sounding so let's run the sid tester and that should reveal the problem directly [Music] um all right well i bumped the machine when it was running and now we have this garbage here all right i pushed down on the multiplexer chip the one with the dirty contacts there and it started working again and the machine is still running so i have a feeling that chip must have really bad legs or something so i may need to i may need to replace that okay so i think the filters everything sounded like it was working but i think the filters aren't working correctly i need to grab another sid chip and do an a b comparison just so i can hear exactly how it sounds uh versus this one all right i placed my known good sit in there and before we run the test again i'm just going to take out this other multiplexer here and i'm going to just deoxit the socket here this is a really cheap single wipe socket whoever installed that one so this could be flaky as well and it might well be the one i just installed as well so we'll add some deoxit to this brand new socket specifically not because of the socket that's because of this ic which has very gnarly legs you know what i know i think about it i think i found this chip in some old foam um the anti-static foam when it gets old it actually starts to degrade and it corrodes the legs and i'm pretty sure that's what happened to this i see i can just see just some remnants of it let me grab my little fiberglass brush thing and let's try to clean off these legs a little bit needle nose there oh yeah this is making a big difference is nice it's making them nice and shiny all right so that should help a little bit i hope um word of caution if you have old ics that have been sitting around in anti-static foam for a long time you should take them out it definitely can damage them the foam starts to get gooey and really hard to get off the legs and the way i got it off is actually soaked all the chips and that foam in 99 ipa which had the effect of sort of disintegrating all the foam okay the machine is still working all right uh let's see here adrian's tools sid tester though we still have an issue there it's interesting which i see is it okay that crashed the computer which one is it seems to be worse when i run the sid tester okay is it is it the top chip or is it this bottom one or is it neither okay i think it's the bottom one yeah it's this one when i push on it in a certain way oh maybe not maybe maybe or is it this one i don't know this is hilarious no i don't think it's the top one because that that's not doing anything it's this bottom one i'm gonna still take that socket out it didn't look good it was not well put in and it's a single wipe and i just hate the single wipe type [Music] all right did that come out it melted it nope i gotta say i really hate removing sockets they just don't come out as easily as uh ics do i don't know why so i'm just gonna melt the crap out of this thing to get this out of here there you go there we go so removing that left two legs behind so not a big deal there they are they just popped out i i pushed them out with the de-soldering iron all right since i didn't remove this the first time i'm gonna inspect oh this is ugly i just want to make sure that nothing is ruined it's a little bit of a mess i got to clean this up here all right it's okay nothing is damaged on the top side okay all right everything on the bottom looks okay as well i have a little bit of one of the holes it's not quite empty all the way and actually one of the vias is damaged a little bit let's see if i can get this thing in all right no problem it's going to be fine so we put that there to hold it in place okay socket's in i'm going to use the loop here to check for any bridges it's kind of ugly but it looks totally fine all right there we go i just popped in the old chip in the bottom one but they're both new sockets so hopefully we are fully operational now without any kind of glitching or whatever make sure those pins are out of the way all right first power on will it work black screen nope there we go it's working just the glitchy cable so that is not related to this machine let's go back to sid tester now okay there it is i think i mentioned early on i like this revision of motherboard the thing i like about it is it's really the picture quality is really clear and it has very minimal jail bars and that's what i love about it minimal jail bars all right adrian's tools sid tester let's do the old bump test look at that okay ignore that it's getting darker that's the cable no more glitching when i bump the board that socket was bad someone's repair was foiled by a bad socket all right here we go again with the uh all tests i'm just gonna listen and report back if i hear anything actually i think it's the filters is the problem let me listen to that again [Music] all right now with that heard i'm going to swap back to the uh the sid that was in this machine and let's listen to what that one sounds like i mean whatever's wrong with this sid is very subtle okay listen how noisy that is wow okay here we go same test yeah these filters do not work properly gotta say that's kind of a strange failure mode i haven't heard this particular problem before chip seems to be working other than being noisy but those filters are not sounding right at all so i'm going to write a big m on this sid chip for marginal it's good for testing but i think those filters not working properly it's going to make something sound fine like i'm sure that the little ramping tones in the diagnostic cart will sound fine but things that really push the sid chip to the limit are not going to sound fine and i heard that as soon as the donkey kong arcade music started with that 8-bit dance party intro all right for the final test we we're going to run the diagnostic harness on this machine i'm fully expecting pretty much everything to work on here unless there's some other hidden problem like one of the 65 26s are bad luckily they're all in sockets so there won't be any issues if i have to replace one of those there we go looks like it's almost done yep it's done and here's the sid test [Music] and that sounds absolutely perfect no problems with that sid test in here and that's why this is not a good diagnostic for to see if your sid is working you really need to run the sid tester uh that i was running there and make sure that you compare the way it sounds to a similar revision of the sid to a known good one so if you look on the internet and hear a good one then compare it to yours but you have to compare 6581 to a 6581 or the sid that's in the short board to the same sid that's in the shortboard all right so this board passed all its diagnostics so it is good to go and that glitchy problem is fixed so that is another repair complete so i'm going to write out a new note i'll put dc again because i don't know what that means we had a bad u13 and we had a bad socket at u25 and those are the bad parts right here so yet another bad moss chip of course and just like on the last machine things were overheating so would you feel hot chips of course this chip was also kind of warm but that chip was really hot so that really again was the giveaway but let me tell you i've had plenty of these moss ttl logic chips go bad and they weren't hot like these ones so that's not always a dead giveaway also one chip that's shorting can cause another chip to get hot although usually you're gonna have the ship that's shorting also be hot so maybe you have two hot chips anyhow once again the oscilloscope came in really handy for troubleshooting and fixing this the bad ship there had two signals on it that looked all out of whack which was sort of the giveaway that that was the bad chip and not this one over here it's not the one i'm pointing to yeah this one right here so i think that is going to be it for this little mini repair-a-thon on the 64s i do have a box down there on the floor with a bunch more to work on so there'll be more coming i think people enjoy these videos i mean even if you're not into the 64 just the art of troubleshooting is still fun to watch and generally these types of techniques apply from one machine to another right so it's useful right anyhow if you did enjoy this video i would love a thumbs up if you didn't you know what to do you can hit that thumbs down button subscribe if you haven't already check out the second channel if you haven't already and i want to give a big thanks to my patrons whose names are scrolling up the side of the screen if you want to become a patron you can do so as well and i guess that's going to be that so stay healthy stay safe and i'll see you next time bye [Music] you

Channel: Adrian's Digital Basement

Views: 81,692

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Id: URhhfijIYM8

Length: 36min 2sec (2162 seconds)

Published: Sat Jan 01 2022