I was completely wrong with my diagnosis of this IBM PC 5160 motherboard

well hello everyone and welcome back to Adrian's digital basement on today's video I'm going to be trying to diagnose and repair this IBM 5160 motherboard it first appeared on a second Channel video where I took apart um a derelict IBM 5160 that had been donated to me and it worked for a little while but then it just stopped working I have a little bit of notes on here so it might help me with troubleshooting but I have no idea what's actually wrong with this so without further Ado let's get right to it [Music] thank you all right so this is the motherboard I wrote IBM 5160 bad Ram at u63 fixed now no post stack error question mark Bank zero I put a question mark these were just guesses now what I'm talking about with stack error is while the machine was running all of a sudden it just said stack error and then when I power cycled it it no longer worked again and you can see here one of these RAM chips is not like the other and this is the one right here at u63 that was the one that was bad originally and I swapped it out this thing has 256k on board so these are banks of 64k each and from my recollection as the note says it just stopped working and that was that now we have a couple good things going for us there's no custom chips at least I don't think there's any custom chips on this board oh actually this thing here looks custom this chip dated in 1984 says d8288 all right well actually this is the equivalent of the Intel 8288 which obviously is part of the regular chipset that makes up the original PC XT and while the 5150 and the XT it looks like this I see just makes up some of the signals that run the bus and the various components on the PC so that's something that I can definitely still find in fact I might even have a spare right next to the CPU here is the Intel 8284 and this also has some function which I can't remember what it is but it has something to do with the PC architecture but also that chip is still something you can find it's not some ultra rare part and that's what I'm really talking about it looks like every single component on this motherboard are standard off-the-shelf Parts meaning if anything on here is bad we can actually find a replacement for it the issue of chips that can't be replaced is more of a problem on later machines because they combine like a bunch of this logic magic here for instance into a single pile chip pal or gal programmable array logic and the issue is those chips can't often be copied or read out so if that chip goes bad if you can't find a replacement you're dead in the water and the motherboard is toast motherboards like the Macintosh 128 and 512 and even the Mac plus look like they all have standard ICS on them but the issue is Apple did use programmable array logic and the equations for those have never been released so if one of those chips goes bad if you can't Source a replacement off another of the same motherboard the motherboard you have is now a paperweight you may have noticed I've been wondering about this IC socket right here I'm pretty sure that this is supposed to be empty a little bit of dust on that socket which implies that it's been empty like that the entire time this board has existed and I just did a very quick Google search for IBM 5160 motherboard and here is one right there that has that exact same IC socket unpopulated and if you look at the top side of this board it doesn't look like any of these traces actually connect to the socket like this Trace here comes out on that side so these just run straight through and this is the socket on the back of the board it has one Trace connected now I think there's a ground plane inside this motherboard potentially a five volt power plane as well so those might be hooked up to this IC but I do have to wonder what this chip socket is for if anyone is familiar with what u84 does yeah please let me know in the comment section below okay time for a little troubleshooting I've just connected a speaker in the power supply let's see if we hear a beep when I turn this on all right there was no beep the power supply was actually shorted out so I think at the minimum we have a bad tantalum on this board here probably on the 12 volt rail so if you look at the power connector here the yellow wire is the 12 volt rail the red wires are 5 volts and and I forgot with the blue white and the orange do but one of them is like power good and I think there's a minus five and maybe a minus 12 on this power supply so we're going to be going from this pin right here which is the third from the keyboard connector and then to these middle pins for ground alright and I'm using the virtual bench so if I short these together there's no beat but we're getting uh 0.3 ohms oh actually there is a continuity feature on here let me try this oh yeah all right it actually beeps from the PC speaker well you know the sound card that's handy okay so to not annoy everyone I'm gonna null these out so I'm holding the probes together I'll squish them as hard as I can and I hit null offset there we go so that just zeros out the resistance measurement just so we get a little bit more accurate of a reading all right so let's just test so there's the resistance from ground to ground so point you know three two ohms whatever nothing nothing nothing hmm okay that's a ground all right so to this blue one nothing 12 volts nothing okay wait a second none of these are shorted it doesn't make sense uh okay five volt rail we're getting 62 ohms that's definitely low ish but that's not a dead short and there's a lot of five volt stuff on this motherboard so okay I'm gonna switch this over to DC I'm going to leave this in the five volt pins there let's turn this on okay I don't know what happened the First Time The Fan was not running on this power supply we're also getting no beep so I'm just confirming that it's working exactly like it was before so we're getting 11.85 volts on the 12 volt rail 5 volts on the orange wire that must be power good minus 11.8 so that's a negative Rail and the white wire must be minus five yep there it is minus 4.77 volts all right so I'm just going to power cycle the scan definitely no beeping now I'm going to give it the old feel test I'm going to look for chips that are very hot so far so good now if you have a thermal camera of course you can use that to help you troubleshoot and keep in mind that some of these ICS like these Intel ones here they probably get relatively warm as it is they're ceramic packages so far everything feels fine nothing is super hot all right so nothing obviously is burning up I'm going to plug in this postcard now the postcard unfortunately will not have anything to display on the numeric display that first showed up on the IBM at 5170 so on a machine like this all this is going to do is show us the voltage rails that's this set of LEDs here on the left and on the right we have clock i o ready frame and reset signals so I'm going to hold the motherboard like this and let's turn it on all right so the way the LEDs look there is normal I'm going to power cycle it just so you can see what it looks like what I'm looking for is that the reset line which is this led right here closest to this little speaker should be on for a second and then turn off that's going to indicate that the CPU is in reset and then the reset circuit releases the CPU and allows the machine to boot and you see that it was on for a second and then went out and then when it went out this led down here came on so this machine is definitely trying to boot it just isn't now I have definitely shown this postcard a lot on the channel you can buy these from eBay or from Amazon they're very inexpensive and if you're working on PCS to be any troubleshooting I highly recommend it of course it's got a PCI connector here and an Isa connector so you can do both with the same card you might be wondering why I put tape on here and that's because this LED display was showing the current postcode and this one was showing the previous code so if this showed like a two this would just show a one as I counted through the post which sometimes can be helpful for troubleshooting to see what the postcode was right before the one it got stuck on personally I found it distracting that there were two so I just put tape over the second one this wire here also is for a speaker that's integrated into this board so you can connect this up to the speaker connector and if you want to hear beep codes it may be a very convenient way to do so I have the virtual bench up on the screen and alongside I have the pin out for this dram right here what I'm going to do is quickly probe the d-pin or pin 2 on the dram especially on this row here which is Bank zero the first part of memory and that all goes back to the fact that when the machine died it had a stack error and I'd imagine on the PC the stack is stored in the lowest part of memory which would be this first bank and almost certainly a PC won't boot without its first bank of memory on later PCS it will actually give you beep codes if that Ram is not working like if you have no Ram I just don't know on the 5160 if that's the case I should go oh you know what I should go Google what the beep codes are for it looking at minus0degrees.net there's not a lot going on with bead codes there are some beep codes continuous beep is like a faulty motherboard or one long beep Too Short is uh some switch configuration errors well I didn't touch those so I know that's not a problem or one long and three short is you have an EGA card okay whatever and everything else down here is stuff displayed on the monitor which we're not getting and when you get nothing it says this symptom has many causes all right so we'll get back to that in a second all right so I've powered this up and let's take a look at Pin two on all of these sockets all right we see activity all right so the first chip there is the waveform and you can ignore that ringing you see at the bottom that's just because of the ground lead I have here it's not not ideal for probing this speed of a signal if I turn this off turn it back on you get some activity there look at that and then it dies so the machine is running let's just quickly check the other lines here okay so this doesn't look good let's turn this off and back on again uh something is weird there do you see that signal that we saw briefly there that was like half height that right there that's not right something's wrong on that data bus line about this one oh this one looks screwy too when I power this on it should look like this first one here see that nothing is half height it's either all full up at 5 volts or down by ground let's check this one that one looks bad too this one as well what's happening exactly here no bad that's no good and the virtual base just went offline this happens sometimes when I'm toggling AC devices off and on like this power supply on the bench here and I have to actually unplug the power from the virtual bench and plug it back in from the back in order to get it to come back to life it's a weird issue with this particular device all right and we're back okay so I realize now that I don't even need to power cycle this like this chip here it's doing that half height thing this one as well yep that's bad that's bad that is bad these are all bad okay now you might be wondering why it's not doing it on this first chip I have a feeling this is a parody chip so one two three four five six seven eight that's probably eight bits and this one is probably used for parity so it's not hooked up to the data bus in the same way as all of the rest so unfortunately I think the fault in this motherboard is not as simple as just a bad ramp chip in Bank zero here I think something else has gone wrong that's causing a bus conflict which is most certainly why we're getting that weird half height voltage thing on the data bus okay so I have the CPU pin out up here and I want to check the data bus lines on the CPU now one thing about the Intel 8088 which is different of course from say a6502 is that it doesn't have separate address lines from data bus lines they are multiplexed so these pins right here are both the address lines and the data bus lines and the CPU alternates between the two and that's actually one of the reasons why the 8088 is not as efficient at the same clock speed as a 6502 and that's because those pins are doing that double duty there are latch chips on the motherboard that latch those signals in so when it's sending the data bus signals out the latch holds those in place and then can send it to the rest of the board and the same for the address lines 6502 has discrete pins for address and data so it takes advantage of every clock cycle to send address signals and data bus signals out or in of course both directions so I'm expecting when I probe the address lines on here the ones that all aren't multiplexed we should just see a nice clear Square wave signal and here we are on address line 14 and it all looks great here we are on the clock signal and all looks good and here we are on one of the address slash data bus lines and it seems okay let me stop it here so you know you have stuff that's up here and then things are a little bit lower but that's still within TTL range this would be 5 volts four volts that's okay if it was down here around three three and a half that's where you get into the nebulous land like on the ram if I stop this we're at like 1.3 volts here that is just not right for TTL signaling so let's take a look at the technical reference for this motherboard to see what exactly is in between the CPU and the ram when it comes to the data bus signals okay so we're on page 28 and here's the main processor right here right here are the address buffers for a 8 through 19 and remember that's because those are not multiplexed so you have standard 74 LS 244s and then you have ad0 through seven and those are the address buffers that get latched to be combined with the other A8 through 19 that can generate all of the address lines needed by the system to address one megabyte of address space and next up is the 74 LS 245 it's a bi-directional bus transceiver and that's what connects the multiplexed ad0 through 7 to the data bus lines now if we follow that line over oh it's to the next page I think it's this one right here there's another set of data buffers oh and there's some more buffers here that go to the memory so the memory is actually buffered twice through two sets or two 74 LS 245s it's actually interesting that this chip is here because when we were checking the signaling on the RAM chips we were looking at this side of the signaling right here well what could be causing those weird TTL signals to not be 5 volts or zero it can only be the RAM and it's very unlikely that all of this memory is bad it's got to be either that 74 LS 245 is doing something weird or it's bad or the chip select or the select Logic for the ram which is this stuff right here is somehow screwed up and maybe it's selecting multiple banks at the same time one way I can try to validate that is I could just remove these three Banks of memory just leaving this one single Bank each one of these chips here is talking to this 74 LS 245 on individual data lines zero through seven and when you look here at the layout on the motherboard each data line on each one of these chips is paralleled to the three chips below it so these four ICS pin two is all connected but normally the select logic would only select One Bank of chips at a time you wouldn't have multiple Banks talking simultaneously so here's a good test to see if the issue is selection logic I'm just going to remove these three chips so that the only chip that's connected between here and this memory buffer is this one right here that means that only one thing could be talking on the bus at a time and you can't be having issues with multiple ICS trying to talk at the same time and here's what I'm talking about for clarity imagine this chip here is trying to send a one to the data bus that's 5 volts and these three chips here are trying to send a zero if they're all selected simultaneously they're going to fight each other and you're going to get something on the data bus that's not five and it's not zero when RAM chips are not instructed through the Razz on the cast signaling to be driving the data bus they are ultimately the same as being disconnected from the data bus entirely so the one chip that is connected and trying to drive the bus is not going to be fighting with the other chips take a look at Pin two okay we're still getting it look at that did you see that still getting that half height thing which helps eliminate that it's not this memory control logic in addition this 74 LS 245 is bi-directional so it has a signal that tells it which direction the signal is going if that control line is bad as well that could be a problem so we're gonna have to go look in the schematics further down to see what controls this IC alright on page 62 we see the ram here an MD 0 through 7 and that's memory data bus zero through seven that's the bus lines we've been looking at Pin two it's also hooked up to pin 14. that's where we've been seeing these weird signals you'll notice here md0 through seven it also comes down here goes to this other Bank of memory it is also connected right here to u20 which is this IC here 74 LS 280. this must have something to do with the parity memory checking so I'm just going to put a dot on that I see because that could be one of the problems right there as well and if we follow this down here it goes to sheet 7. let's take a look at that see where the memory data bus goes md0 through seven is probably just going to the other two Banks of memory so there's one bank and two Banks yeah okay okay so here we go there's the ls 280 so that could be an issue and if we scroll over here right here is the ls 245 u9 which is this IC right here next to the slots it's a Fairchild ls245 so that could be a problem now right here are two signals that control this there's the dir pin one that's Direction and then the queue which is the enable signal when it is low it actually enables this IC so this is the direction pin one and that controls which direction the signals flow through this IC whether you're reading or writing to Ram alright so you see some normal looking activity there on the direction signal so now I'm on the enable pin for this IC and there we go we see normal activity on it and there it just goes low but I think the computer is just completely crashed or Frozen right now let's check pin two on the round yeah it seems like it's just sort of dead in the water back on the schematics here the enable pin let's see Scrolls down it comes from Ram address select sort of has some other logic there and the direction pin comes from X memory read write now I don't know if logically those signals are working correctly the direction signals controlled by this 74 LS 74 here it's not an impossible failure to have an ls-245 that actually keeps the data lines connected even when it's not enabled so I think what I'm going to do is grab a second oscilloscope probe and I'm going to check the enable pin on the 245 against what we're seeing on the data bus lines to the RAM chips because when the ls 245 is not enabled we shouldn't see anything happening on the Ram at all and unfortunately this chip is not in a socket so I can't just pop it out and replace it to see if that is causing the problem okay we have two traces the yellow Trace is the enable line for the 245 and then the red Trace is on the data bus on pin 2 right here so let's turn this on all right so it ends up in this state here where it's completely enabled all the time I think the machine is just sort of dead let's turn this off and on I'm gonna have to hit stop when all this is running here so it is stopped right now let's turn this off and take a look at what we're seeing so remember the yellow trace on the top is the enable signal for the bus transceiver so that chip is only turned on when this signal is low which is right here and looking at the waveform I don't really see a lot of Rhyme or Reason this address line was high at that point and the chip was off now that doesn't mean that the ram wasn't trying to actually drive the bus because it can still be selected it's just when that chip is turned off the ram is doing driving the bus but it's not doing anything it's not connected to anything what I'm going to do next I'm going to pop out this Ram chip right here so so nothing can drive the bus except for the ls245 and then the only other thing that's connected is this 74 LS 280 chip here and I don't think that ship is supposed to drive the bus at all I'd have to look at the data sheet but I am pretty sure that's these are inputs only and then it outputs either even or odd which is how it calculates the parity so this is the data sheet for that 74 LS 280 it's an odd even parity generator slash Checker and here's the function table and it does show that these are all inputs a through I and it has two outputs here even an odd so with that said let's turn this back on and let's take a look at what we see here this right here is absolutely telling us that one of these two chips is faulty and I have to say I'm actually kind of leaning to this 280 chip but it still could be the ls245 when the ls 245 gets turned on it seems to draw this data line all the way down to zero and then the OS 245 is turned off here and here and then something is obviously driving the bus now I haven't mentioned this and I don't think I saw this in the schematics yet but there could be something pulling up those data bus lines to 5 volt that's totally possible it's not always the case but it might have pull-up resistors let's go check that out no I don't think there's any pull-up resistors there because it's not on this sheet and md5 the MD lines come up here and they just go straight to that and there's no pull-ups pull-ups would be shown on these schematics if they were there they would look like this there's a pull-up resistor right there that's pulling up through 4.7 K to 5 volts on whatever Line This is you know what I just had a thought that I might have been going down the wrong path the whole time here I talked about earlier that there were no pull-up resistors on the bus here well the thing is that could be throwing me for a loop and I should have realized this sooner when you don't have a pull-up resistor on the bus when nothing is driving the bus it just kind of floats there and that means that ICS that are connected to it can potentially drive the bus to weird levels it's not necessarily just going to be zero volts but there is so little current driving the bus that it doesn't really matter and as soon as you try to drive that bus either high or low there's no problem because you're only fighting against a tiny amount of current that was holding it like in the middle there somewhere maybe that's what's actually going on here so I think I'm going to grab a resistor like a 10K resistor and I'm going to pull up that data line up to 5 volts and let's see what happens exactly so there it is I stuck a resistor between 5 volts and pin two which should pull it up with 10K and let's take a look at how this looks once I power this board up ultimately if everything is working we should only see 5 volts or we should only see zero volts on this line now I hooked up the oscilloscope to the enable pin so we can take a look at how that looks okay let's pause this all right so we see an enable and it drives the data bus to zero and then we see another enable but doesn't really do anything with the data bus right it's still sort of slowly rising up to five volts we are definitely not seeing anything strange on the data bus anymore right there's none of that weird half and half five volt stuff so I'm going to say that weird two and a half volt thing we were seeing was normal and it just had to do with the bus floating and it's not a problem at all now I'm used to fixing Commodore 64 so I'm used to looking at the way the bus looks there I've never worked on a 5160 motherboard before so this is a bit of a new territory for me so you're learning with me here this is a normal process what's probably Happening Here with these two enables to the 245 is the first one is trying to write to the RAM chips it's trying to drive a zero into this particular Ram chip and then probably what happens is the CPU attempts to read from it which is what's happening right here if the ram chip were in place we'd see a zero and then we'd see what the ram chip driving the bus to ground right here as another zero so the ram Chip's not installed so there's nothing to read back except for five volts or you know it's raising up to five volts and that is normal and when I zoom out everything looks normal it's either pulled up to five volts or it's driven to zero probably from the CPU now there's still a possibility that everything's working perfectly and it is the bank zero Ram that's the problem I kind of went directly down the possibility that there's a problem with the logic chips without just thinking that everything's actually working perfectly like this is normal what we're looking at and it's just the ram that's bad so before I go desottery any chips I'm just going to quickly pull out some of these RAM chips here and stick them in Bank zero and let's see if that has any effect at all all right these RAM chips have been removed I put them up above there and I took these and I stuck them in Bank zero so let's just see if this actually works now now the speaker is hooked up but I don't have a video card hooked up let's just take a look at what the activity is on one of these RAM chips I'm gonna go out on a limb and say this machine is still dead as a doornail we turn it on let's see yeah we see some activity and then it all just sort of goes nowhere what's interesting is with bank zero in there when I turn it on it does seem to do quite a lot more before it kind of goes bad see all this activity there so I am still thinking that there's probably nothing wrong with these two ICS and the problem is something else on the board I mean total red herring in the wrong direction for me so I think the next step is to try some of the diagnostic ROMs that are available for the 5160 and there are two listed here on minus zero degrees there's the landmark diagnostic ROM and then Rudd also created his own let's try this one which I think is pretty old and been around for a long time click here for the ROM image all right we have this motherboard and it requires a single 27 256 eprom and it goes into u18 so there it is there's the bin file let's use the mini pro sometimes with these old chips and the mini pro um programming it a couple times probably makes it work can make it work a little bit more reliably and yes you can program an eprom with the exact same image multiple times and it just can sometimes reinforce the data that's stored in the chip u18 is this IC right here this is the BIOS chip and with our diagnostic chip says to check the dip switches are set correctly for the correct Banks of memory let's just go to on and on which is uh only 256 K the first bank here all right let's turn it on see what happens it's beeping that's a good sign all right so it says to check the manual for the beep codes all right so the beep codes are here so there are high low tones we have up to six of those and then you have short tones up to looks like nine of those okay so that was five and nine which is simply cannot initialize the monitor I hope that basically the whole problem wasn't that I didn't have a video card in it the whole time what let's plug a card in and see what happens here's a CGA card which it says this thing works the best with unfortunately my capture device here is not working and it's not the capture device the Elgato it's actually my lab computer up here the USB 3 ports have quit working on that thing and if they're on board the motherboard and there are no more slots on that thing so I have to buy a new computer for the lab so I'm going to be hooking up the HDMI the RGB to HDMI to the monitor here so unfortunately you're only going to be able to see what's on the screen through this device here okay video card is hooked up let's see what we see oh hey look at that it is running Diagnostics let me move the camera all right hopefully that's working so wait a second everything is working was this just a memory problem the whole time obviously that's a video card test okay keyboard controller what I'm wondering if the keyboard failed because I don't have a keyboard plugged into the computer I should plug one in I guess run this test again it just really seemed looking at the oscilloscope after I changed the ram around when I still have the stock bios in there it just sort of stopped doing anything and the speaker was hooked up I was assuming it would beep if the video card weren't installed maybe not well okay I'm going to swap back the original bios because it looks like everything is passing obviously the floppy stuff will fail original bios back in and yeah about a minute later nothing no signal out of the CGA card at all I'm going to quickly go over all the switch settings here just to make sure everything is right all right well let's try this again no it's definitely not coming up here even set to CGA could there be a problem with the ROM bios I mean that is possible I popped the chip out here just checking that the pins aren't banned and they are not and that is definitely the IBM bios chip there I'm going to put back in this diagnostic ROM here and then just let this thing run through its tests there it goes let me unplug the speaker okay it's unplugged all right I am back from dinner and I've just left this thing running it looks like it's uh passes 43. everything on this side looks fine although slow refresh has one failure although it passed on the last time but okay I was just about to talk about the next error here's the error that is suspect system bios failed right here now I just assumed early on that this failure had to do with the fact that I replaced the BIOS with the diagnostic one but over here u33 super soft ROM checks on pass so this is something else potentially over here to minus zero degrees I think this is the key thing the ROM does not require the IBM ROM in socket u19 to be present however if not present expect you 28 system bias to fail that is the one that was failing so I've grabbed a fresh blank eprom here and I'm just double checking that it is blank and it is and these are the BIOS files that I downloaded from -0 degrees and there's a readme file right here u19 is the IBM part number five and a whole bunch of zeros 27 which matches the chip on the motherboard right here and that is 8k in size they have included a version of this file here which works on a 27 256 and the image is reported are repeated four times so that it can work in a 27 256. awesome so I'm just going to load up that file let's program this chip out with the chip that's potentially bad maybe maybe not we'll see out with a diagnostic ROM and I'll put back in the stock ROM that goes into u18 all right what's gonna happen look it's freaking working it's actually working that's booting the computer and everything look this chip failed failed I can't even believe it oh that is one working IBM PC 5160 motherboard wow I may as well put back all the RAM on this board that I was accusing of being bad I have to apologize to the ram like if it had feelings its feelings might be heard because I accused it of being bad and causing a problem and then these chips I'm sorry you you never had a fault I'm very glad I didn't desolder them that would have been unnecessary and potentially damaging to this motherboard and I'm just going to change switches three and four to off that enables all 256k of ram plug the speaker in and here we go oh we're only getting 192k you probably couldn't even see that 192k of ram implies we're getting three Banks of memory working and the fourth is malfunctioning so I might as well pop this XT diagnostic back into this motherboard Let's uh see what it says about the bad memory there it is bit number one it's saying there is a problem so we know right off the bat that that failed bit is in this third bank so I'm gonna go investigate that over to the schematics here to figure out exactly which is bit number one here it is md1 goes to u32 u47 down to the next page it goes to u60 and u77 so that one should be the chip well I see the issue do you see the problem here with u77 yeah that ship is in backwards so I probably just killed that I see but let's swap it around you know it might be working who knows funny is that when I install this Banker Ram I thought I paid attention to the orientation of the chips clearly not all right Ram Diagnostics round two if you're noticing some Shimmer on the picture here don't worry about that that is just the RGB to HDMI not being perfectly synchronized to this CGA card I just haven't gone in there and adjusted it now some ICS when you put them in backwards like eproms immediately die immediate death but Ram it can be pretty resilient um yeah it's fine now that actually is fine that chip survived this whole motherboard is a Survivor it was left for dead in that PC 5160 that I got and um it just continues to work except for the fact that this ROM chip decided to give up The Ghost and there we have it everyone everything has passed in fact it's funny because the floppy Drive was failing to read before even though the card that's in here is the original floppy controller from this machine maybe it was relying on some bios routine that was failing because of that other chip that was bad I mean everything is passing now this computer is totally working so because I know people complain about it I'm gonna put a little sticker over this eprom here so it will not get erased or whatever 5160 u19 and let's take this diagnostic ROM out which I'm going to erase I won't keep that but the original chip back in here for u18 turn on the machine make sure that it works as it should there it is counting up the ram look at that when I wasn't paying attention I think it got to 256k let's run check this to see how much free memory there is there it is 256k of total memory and there we have it one fully functional IBM 5160 motherboard where the only fault was this failed ROM chip so it gets the big old X on there and with that I hope people found this diagnostic video interesting talk about going down the wrong path over and over again I was totally off on tangents thinking that things were wrong with parts of this board that had no fault at all honestly that's kind of how a Diagnostics go when you're not making a video about it you're going off on different tangents constantly trying to figure out where the fault is unless you're so experienced at repairs that you're able to zero in on exactly what the problem was I've never worked on or tried to repair a 5160 motherboard other than broken tantalums which I'm pretty sure this has that because it looks like one of the tantalums here is missing I think originally this thing had a shorter template I just broke it off the board maybe I should replace that it's just kind of how it goes when you're doing repair work especially on things that you're not really familiar with of course most people don't make videos while they're doing repair work so you don't really see any of those tangents you might just see what the end result of the problem was but when you're working on something that you've never worked on before like this board with me bring up the schematics and just start studying how things work and then watch out for the red herrings like the bus stuff I saw here with those middle voltages which was really just a floating bus as you do more repairs you start to gain more experience and you'll know to look for those things and you'll be able to rule them out very quickly with me even though you've seen me do repairs on this channel I still am quite the novice and it takes me a little bit of time to think through what I'm looking at before I realize what's actually going on case in point was that bus problem there so the repair of this motherboard all came down to that really useful diagnostic ROM otherwise I might have gone off on some other tangents trying to figure out what was wrong with this board although the fact that these were in sockets even if I didn't have a diagnostic ROM I could have at least done a compare feature on the mini pro to both of these ROM chips and hopefully I would have figured out that that other chip was bad it's also kind of interesting if you go back to the original video about this that the machine was just working normally on the bench I wasn't even touching it when this chip failed and when it did the computer crashed and then never worked again so it's funny how failure modes like that can just happen and I've definitely had that kind of thing happen with stuff that was put away in anti-static bags in boxes where it works when I put it away and I take it out and it's now broken in some way so I have the dead parts bin here let's pop this open pretty full of ICS there this IBM ROM oop it didn't want to go in there it is it's in there now it's in its final resting place so that's definitely it for this video If you enjoyed it I'd appreciate a thumbs up but if you didn't you know what to do hit that subscribe button if you haven't already comments down below big thanks to my patrons their names are scrolling up the side of the screen really appreciate the support if you want to become a patron yourself you can do so at the link in the description below check out my second Channel as well if you haven't lots of videos over there including the one where I think I showed this although maybe this was on the main Channel nope I think it was on the second channel it's been going for a little while now it's got like 28 000 subs or something like that slowly creeping up it's just really good so that's it so stay healthy stay safe I'll see you next time bye-bye [Music]

Channel: Adrian's Digital Basement

Views: 92,743

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Id: StyY-6_DjJ4

Length: 41min 21sec (2481 seconds)

Published: Sat Nov 20 2021