Don't use a blowtorch to fix your C64!

well hello everyone and welcome back to adrien's digital basement on today's video we're gonna be repairing another commodore 64. not this one this is my zip64 we'll be taking a look at a motherboard that is a real basket case got some severe damage on it so without further ado let's get right to it [Music] all right so here we have a 64c short board this is the much later version or the very latest version because the pla chip which is this large ic it doesn't even have the color ram i see off to the side it's actually integrated into this ic so this was pretty much the last 64 made while this design was the last one made henian sent me several of these boards and i think he was in germany so this will be a pal board one giveaway is of course no toggle switch here for the channel selector on the rf modulator and another giveaway is this little jumper pad right here it says short for pal or open for ntsc and it has a little blob of solder on there so it is closed the loop which should enable pal mode to the misting 8701 clock generator in addition to this little jumper though you do also need a new crystal oscillator the correct value for pal which i am forgetting right now i think it's like 17 megahertz or so and the ntsc one will be 14.3 megahertz so we can tell by my diagnostic note here from when i got this we have no ram so someone stole the ram and the bypass caps like why steal the bypass caps we have no clock synthesizer chip that's the a701 we're missing the sid chip of course and there is a damaged socket over here for one of the rom chips this looks like a bit of a hack job so i must have taken the rom chip out stuck it in here and the problem is is if you remove an ic and you don't clean off all the solder on it and you stick in one of these cheap dual wipe sockets you get from china when you pull that chip out it's pretty much guaranteed not guaranteed but it's there's a good chance it's going to do this kind of damage to the socket that does not happen with this round hole type these are harder to get chips into but you'll never have this problem with the socket getting damaged like this when we flip the board over [Laughter] oh this is carnage i mean look it's like burned over here and what did they use to remove this chip so i think the very first thing i need to do is try to clean this up i need to remove this socket get all this black gunk off clean out the holes for the ram and let's see if we can revive this board all right so those pins are left in there and this kind of goes back to what i talked about in a previous video on these repairs if you're trying to remove a chip that you know is bad like say one of these ram chips use some cutters like these ones sitting right here and you cut away the top of the package leaving just the pins in the board now what i'm going to do is i'm going to use my soldering iron a little bit of solder and some tweezers and we're going to remove these pins from the board so we just add a little bit of fresh solder onto the tip and you place it down at the bottom and those pins should come right out very easily do not force them out they should basically fall out once you heat up the the pad there's another one and then this last one here it's going to be a bit harder because it's on a ground plane there we go it came right out and we do the same thing with these and the reason why these like stayed behind the board is because they are on a power plane there you can see this copper here makes it harder for the desoldering iron to melt the solder all the way through the via so kind of leaves it on the top and there we go so that's it that's all the pins out of there now i just have to clean that up now you could use some good quality solder wick i don't know where mine is i think i've misplaced it but because i have the desoldering gun i'm going to use that it's a lot easier i'm just going to try to clean this up a little bit wow it's just so bad i'm just using 99 ipa to clean this and a brush just because i want to have a better look at what's underneath oh boy all right so what i'm going to do is i'm going to reflow solder into each one of these and then i'm going to clean it out with the de-soldering iron [Laughter] all right well i did my best trying to clean this up and uh it's pretty much a disaster so what i have here is some acetone i'm just trying to clean off some of this flux it just is not coming off oops i just built some on the bench it's not coming off with the regular ipa acetone is definitely a bit stronger i just really am trying to reveal what exactly is going on underneath here looks like there's at least two vias on the top that are completely gone so yeah these two vias on the top there are just gone there's really nothing to solder onto and then it looks like that trace that's right there might be damaged as well i need to double check that let's check the other side whoa let's slather this on the board is actually warped right here where the rework has been done in the past okay but the acetone is really working really well look it got all that massive pile of the gunk off there when i talk about acetone i'm using nail polish remover which pretty much you can buy anywhere in the u.s at least 100 acetone i think i got this at the dollar store be careful though because if this drips onto abs plastic or other types of plastic it completely melts it and deforms it so really you got to keep it off of abs seems to be fine on pcbs and stuff although i wouldn't pour it on everywhere because you never know there might be components that it might damage but as you see here it did help a lot it's not magic though the warped board here is not going to be fixed with some acetone nor are these burn marks over here let's put some ipa back on here i feel like you can really see the burn marks when i put the ipa on there unbelievable i'm thinking this fiberglass pen may help as well so i'm just gonna try to rub this down a little bit maybe that'll clear things up a little bit all right i've broken out the andenstar hdmi microscope so we can try to get a better look at the damage to this board up on the top side of the board here can see some of the substantial damage up here in the corner so this trace here is obviously not connected to that via anymore and that via had a trace that trace originally went to right there and it's been lifted so we're going to have to uh replace that let me just try to break this let me break that part off there since that's not doing anything but could cause a short over on this side we do have some damage but it looks like everything is still connected uh is that normal that trace that's wobbly like that i can't imagine that's how it was originally i mean this is this is ugly but it should still work all of this here this right here looks like it actually is broken doesn't it over on this side here this uh via is not in the best shape but it should be okay i don't think anything connects to it on the top side that you'd think is broken but i think that's just paint on there yep that that scratches free the rest of these vias up to there look okay this poor trace here has been mangled quite badly as well but i think it should be all right and here we are on the back side of the board so these traces are a bit of a disaster but i think it should be okay nothing attaches to these two pins on the bottom this stuff all looks connected i mean for better or for worse the pcb is quite damaged and everything here is okay that one's just a bit bent over to the other side we have just tons of damage but nothing is connected down here anyways so it is okay hopefully i can get the pin through there again yep look at that one wow it's just mangled it's so mangled up might not be able to get the pin through there everything is okay there's nothing actually connected on the bottom side except for like this one here so yeah it looks like we if i can get the socket in there we just need to connect up two pins on the other side well it'll be on the back side but those two top traces are the ones that are damaged all right while i have the microscope connected let's just take a look at the ram here just to make sure that none of this is damaged no everything looks completely fine here no trace damage whatsoever there's a good view of the burned part of the pcb poor thing looks like everything is still connected though and here is the back side of the ram other than damage to the board um everything is okay from a pin standpoint no problem there will be any issues putting a socket back in there all right i have the two sockets inserted into the board so let me flip this over and connect them up as best i can at least the ram should be easy and then i will do the barge wires now remember on the back side like some of those vias were just gone at least on the back side but they were there on the top side so they are partially damaged so you have to make sure that you still do solder those pins so i applied heat and then i added solder and it allowed it to go down into whatever was left of the via and uh this pin was an example this corner pin and i remember that was one of the wiggly traces that were there so i have the multimeter here let's uh tone that out pretty sure this one should go right there to this via and it is connected so like i said even though on the back side right here there was like seemingly nothing left it did actually make a good connection between there and um that trace now over here there were some traces that were all wiggly and exposed i think it was like this pin here went to there i want to make sure it's not shorted to these pins and it's not and that's just because it's all very close together right there i spray a little bit of alcohol on there and i rub it with a brush might make it a little easier just to see what's going on because there there is a little bit of flux residue from the soldering process so yeah i was just double checking that these pins here weren't shorted to this trace and they weren't all right well this was my little diagram that i made and it was these two top pins on the rom chip so that and that should have connected to that pin and that pin on this rom and of course since there's no badge yet that's not connected there or there so let's flip this around and run those badges i'm going to use the thin wire which is wire wrap wire and what i'm going to do is i'm just going to kind of rough the length out doesn't need to be perfect i'll cut it more in a second and then you just tin the ends oops yeah i get off there we go and i'm just doing the ben heck style here where i'm basically melting right through the insulation to make a connection i saw him doing this i don't remember i think he was building like a portable atari 2600 or something like that and this was the method he used that just uh made it a lot easier to get the exact wire length you needed one of the issues with this particular wire though is uh it's very heat resistant to the insulation so you really have to melt it to uh try to get through it so we should be going from this top pin to here we are and the bot next pin to the fourth one down and we are and i think the next one down should be this one and it is okay cool so theoretically that should be it okay i do need the bypass caps in here and i need to make a rom chip that is compatible with this one here all right i installed a couple bypass caps i actually couldn't find my bypass caps hundred nano farad so i took these off a dead board an old motherboard i also grabbed another 8701 from a different motherboard because for testing this thing will not work at all without an 8701 but a sid chip and this rom chip are not necessary for testing because i can use the dead test cartridge and what's useful about the dead test cartridge is it bypasses all the onboard roms which on this machine are these two chips here and can work without them so videos connected dead test is in let's plug in the power see what happens oh hey look at this dead test zero page this dead test looks a little bit different than i'm used to but i think that's what the eeprom is on here i i have an enhanced version here dead test version 1.20 i think this was a community project to enhance the dead test a little bit so it's testing the screen ram right now which is inside of the pla ignore the fact that the video is sort of flickering in and out a little bit getting brighter and darker that is my cable it is a bad cable i need to replace this all right well the ram test the color ram the screen ram stack is zero page all passed that's a good indicator that this board is pretty much ready to go i just have to add a rom and we need to add a sid chip and maybe we'll have a working 64c okay out with the dead test and this is the rom chip that's missing see 901 22501 same exact chip that's used on the original 64 boards so with that in and the sid missing let's turn this back on we should get the basic prompt um no not quite i also have to say that this machine is jailbar city just look at those jail bars okay i'm going to stick the easy flash in okay it is working oh i wish this wire were not bad okay i put a new cable on so it won't be flickery so badly with the video okay there we go now it's a solid connection so i think this rom that's not working which of course is the socket that i just replaced i think it's the character rom oh and look the machine just blanked out i wonder what is happening here i think the problem could be that this cartridge slot just needs a little bit of deoxide in there all right let's see if it works now and glitches out okay i think that was just a bad connection in the cartridge connector because oops that was me pushing a button on the easy flash seems to be okay now but that is not going to fix the problem with this uh rom not working and i know this is rom chip itself is good in fact what we can do is we can test this inside the retro chip tester let's quickly do that unfortunately i lost the footage of me testing this chip but it did come back as a c64 character rom so the rom is totally fine so the next thing i want to do is install a sid chip and test out easy flash three all right sid chip is in let's turn this on okay we're getting this again uh let's see why don't we use the diagnostic cartridge so it's not even booting the basic power this on okay this is definitely running we haven't run this yet that's the regular diagnostic right only around the dead test so far all right it's very interesting it's doing the ram test i'm noticing some slight flicker in the image and i've changed the video chords so that's not the problem now uh-oh pla test bad that's not good because i don't have a replacement of these types of plas kernel and basic rom show is bad but the character rom which is the one i replaced here shows as good so i should realize the blue screen when i turn it on without a cartridge is not the character rom it is that bad basic or kernel rom showing its ugly head this chip right here is a combination of the basic and the kernel on this later version of the c64 originally of course this was three chips the thing is this rom that has the kernel and basic must be partially working at least because it's impossible for this diagnostic cartridge to even work and earlier of course we had the easy flash booting as well it might actually still boot let's just give that a try so we turn this on ah there it is so that is still working i think what i'm gonna do is reflow all the solder joints on that rom chip that large rom chip because some of them looked pretty rough from this horrible abuse and rework that had happened to the character rom chip i can definitely say this chip doesn't look like it was ever removed if that reflow didn't have any measurable effect then i'm going to take that out and we'll test it outside of this board and because of all the trauma that this board has suffered in this area i'm really suspecting that this rom is problematic more so than the pla so let's give this a try with a diagnostic cartridge again okay still showing that rom as bad now it goes without saying that a bad pla can make roms so bad because the pla is what selects that raw the rom can actually be bad and i think it can falsely say the pla is bad but also the rom can be good and the pla might be the problem and you know you kind of have both interacting with each other causing an issue let's try without the cartridge see if we get anything nope okay all right i think the only thing i can do now is take that chip out and verify it it's a regular eeprom or i can read it in a regular e perm programmer like a tl866 but i'm just going to test it in the retro chip tester pro and we'll see if it's good and if it's good we're in trouble because that means the pla on here is bad okay as i suspected there's no problems underneath here so i really don't think well other than this rip trace right here we knew about that one and uh this one we already knew we had to fix so we had those two badge wires so those uh but yeah everything else here seems fine so no issues and everything on the bottom looks good that that chip came out pretty easily so let me just uh straighten these legs out a little bit and we grab the retro chip tester pro that goes in there like so so it's saying it's 128 that's fine and that's because it's the same chip on the 128 and on these particular boards so that's a problem because clearly this chip is working fine doesn't mean that there's nothing wrong with this chip it might be marginal and the chip tester can read it okay but in this board it's not happy so i'm gonna still put a socket in anyways all right here we are on zimmer's let's find the rom we need let's see here 64c it's a 16 kilobyte 23 128 rom it contains the basic interpreter and it has the kernel so this is the one we need and it has exactly the same part number as this chip here all right we'll load that into here there it is and i have an eprom in the programmer here so let's program this just for good measure i'm going to hit program a few times that's kind of what i do with these older chips this particular one has a 21 volts programming voltage which is the upper limit of this particular tl 866. i have the first generation one which uh unlike the later one as you see here can actually go up to 21 volts okay the eeprom is in the socket let's give this a try we'll know pretty quickly if this is working because of course um we will see that white or the basic screen if all is good but if it still doesn't work then this rom is actually good and there might be a problem with the pla here we go wow it's even worse now we're just getting a total black screen we'll know that for sure by putting the original rom back in of course we should get at least the blue screen we were getting before oh and we're not so i made something worse so my fixing is actually breaking all right so let's try the diagnostic cartridge again not the dead test but the regular diag let's see if it comes to life oh look at that interesting it's so strange that this runs their pla still smells bad it's very weird that this works because usually when you have no kernel rom and no basic you can't even run this diagnostic at all yeah same same bad thing showing up there what the heck is going on this is so odd if i take the chip out entirely and we turn on the computer okay i guess you don't need this chip in there kind of flies in the convention of everything i always thought about this diagnostic rom requiring the kernel and the basic at least the kernel to work clearly not just for fun let's pop out the character rom i don't think this is going to work anymore yeah okay that's what you get i am kind of curious if this cartridge works without the kernel rom in there nope so easy flash does need a working kernel and basic all right it's time to break out the oscilloscope here okay so we need to check out the schematic so here's that rom the one we're talking about the 27 or 23 128 this is the left part of the schematics and the lines that go off to the right side go over to this page and you see here is the character rom so the character rom has address lines 0 through 11 and those two botched wires i added were probably 10 and 11 but the basic and kernel rom also has 12 and 13. so we need to make sure that those are connected now it is connected to address line 14 on the cpu and that's because of see the addressing there it's e 0 0 0 0 to f f fff and a 0 0 0 to b f f two different blocks of memory which is why address line 14 is connected here as opposed to address line 13. all right so the still scopes up on the screen let's check address line 12 and 13 are connected properly so there's pin two and let me turn the computer off and on let's make sure we see activity here we are not getting any activity uh wait a second what's happening here okay that was weird oh i'm confused okay so i'm on the actual pin of the chip and you see there it's sort of doing nothing but when i go down onto the socket there's actually it's actually high is this a problem oh look at that when i push it down don't oh man okay so when i physically push it it makes a connection that's weird this i think this socket i installed is actually bad let's go to this eeprom since it has longer pins problem is this chip i took out the pins are much shorter than they should be so maybe they're just not making good contact in there okay let's try this again so i'm on the pin on the chip and we turn it on okay this is actually making contact so i guess that's uh you know this is correct what we're seeing here if i turn it off turn it on yep okay and then pin 26 okay i'm on pin 26 let's power cycle the computer all right looks the same so those are definitely connected i don't need to test the rest of the address lines because all of those are going right through this eprom they're you know connected underneath the board here and then they go to the character rom and the character rom is working because we see it working with a diagnostic cartridge so all those address lines are fine and they're making its way through including those two barge wires okay so one thing i'm curious about i'm on address line oh what is this one seven i think it's the top pin on the the rom next to it i botched it over when we turn on we see nice square waves in fact let's look at all the address lines the other ones i mean these all look like really nice square waves okay yeah see that square waves it's just when we look at two we don't see square waves we're seeing that weird triangle wave which doesn't seem right and then it's all stuck at the top while these other ones are bouncing around i'm gonna remove this eprom entirely let's just double check that yeah see same thing but if we go to the next pin down then we're seeing nice square waves okay i just realized what's happening so address lines 15 through 12 on the cpu when we see that curving wave it's kind of indicative of a pull up resistor when the bus is floating and if we follow the lines down here there it is right there address line 12 13 14 15 is pulled up to 5 volts at 33k and i think the reason for that is unlike on the regular 6502 just the old standard one that thing cannot tri-state the address bus it means that that cpu is always driving the address bus but on 6510 i think on the later 65co2 it can actually disconnect itself from the bus both the address lines and the databus lines for allowing like a bus mastering or a dma function to happen and on the 64 the vic chip does need to talk to the ram and also the rom the character rom in order to read that content out to display it so i think that's what's going on is all the lines that go to the character rom are being driven by the vic 2 chip and those extra four lines there which are pulled up aren't so they added a pull-up resistor to those all right so the address lines are all working fine on this machine as are the data bus lines because the machine is able to access the ram and do other stuff all that leaves us is the chip select line and right here is pin 22 on the rom there if we go over here that is coming right here from the kernel basic pin on the pla unfortunately let's take a look at what that looks like so i am on pin 22 and the rom is not installed well let's see what we see okay well we have activity on it and that's coming from the pla all right the eprom is back in and let's turn this back on yeah i mean that's apparently normal looking i don't know but we're definitely only getting a black screen so it's definitely worse than it was before i just need to go through all of these pins let's check for any issues here all right here we are on pin 27 and this is weird so we see this activity down here and lit 27 here says that this should be pulled to 5 volts as uh as is this pin here pin 28 and pin one but that is not with the eprom out what do we get on here same thing oh and i'm trying to figure out where that pin goes i see it has a trace it seems to make its way under the character rom let's uh take that off i'm breaking out the sharp probes here because i'm just really struggling i mean it's annoying that it's not right on the schematics obviously so this trace here kind of loops around under there looks like it's right here on the board let's poke through yep there it is and then it looks like it's right here yep and then it goes to what should be a via under the socket here and it's not connected see if i can show that all right see this little silver blob there the trace is right there and it goes into that and yet there's no continuity if i touch this it's not working and yet that has continuity to the trace right up to there so this must be broken and i didn't notice it in the microscope so i'm just gonna try to scrape this away and you know what i'm gonna have to do is cut away the socket so now i cut it away you can see what i'm talking about so i'm gonna go from here and this trace right here so there it is and yet should be going right to that and it's not and definitely indeed the trace is damaged and i guess i missed it so i'm going to use this uh pen here scratch some of that away there we go and let's tin that and i'll add a little tiny piece of wire onto it okay that should do it let's see here all right it's definitely continuity now let's see where that via is going which is that one a trace comes up here all right goes to this via which is connected to that pin let's see where that goes okay goes to that which goes to there which goes to there which is jumper to this oh wow okay so it's jumpers pin 27 on a 128 eeprom is required to be high all the time for the rom to work but on a 256 eeprom it's actually an address line and would allow you to select between two 16k rom images almost as if commodore built in support for having a switchable rom like jiffydos in the machine i don't know how taking this out made that break underneath that chip but it certainly did i think that just needs to be pulled to 5 volts for the rom to be selected so let's put this back in see if we at least get to back where it was kind of working i think at this point now with this fix it's going to give us that blue screen still not going to work i think there's still something else wrong with this machine yeah okay we're back to where we were before so we're kind of getting a semi-working system but there are definitely issues still with it i don't know this thing is a basket case because of all this hidden damage let's see if the easy flash is working like it was okay it's working again so this chip is sort of working but clearly not fully okay so we're back to where we were now that trace has been fixed that means that this rom is getting selected fully uh did anyone catch my issue there i had the character ramen upside down oh dear oh dear hopefully it's not damaged these chips are pretty resilient to that there we go it's actually working fine okay i'm running the diagnostics let's see what we see uh pla test is now okay what this is crazy it's now wait wait a second is this thing fixed is this thing actually fixed it was that bad trace the whole time what oh no you gotta be kidding me i guess it was that trace the whole time and then i thought it was all bad and the chip isn't upside down oh god oh boy okay i'm going to reinsert this sid chip and we are going to try to have an 8-bit dance party easy flash into the machine i'm going to use a controller as opposed to a keyboard i just don't have a keyboard handy all right let's see if this works oh my god all right uh adrian's tools um oh wait i don't know the sound on him wasn't ready for this [Music] it's working and of course it's really slow because it's a pal machine and this is the proper speed for the music [Music] oh man i can't believe it okay so before i claim total victory on this basket case of a machine let's actually do the diagnostic again with the test harness connected and just validate fully validate that everything is working okay i think we're ready powered on i'm using an official commodore loopback for the keyboard as opposed to the one that came with this kit both work oh come on come on come on almost there oh it's working that's it this machine is fixed it's freaking fixed okay so let me assess what i've done here the entire problem with this machine entirely was carnage from this rom being removed the original repair and i'm putting that in quotes only had a single barge wire on it which is uh this little yellow one here which was clearly not enough to make a working machine because it needed two barge wires on the bottom due to damage caused from that chip being removed but in addition that trace that was under the rom chip was also damaged and i missed that even when i was looking through the microscope which is totally my bad and because of that i removed the original basic and kernel rom which is sitting right here and i put in a socket and an eprom and once that trace was fixed this machine is all good but i guess the problem now is that these pins on this uh original rom which are a bit short just don't make good contact in that socket which is a little weird because i haven't really had that problem ever before but if i push down on it hard it does work but um i'm just going to try one more time with the original chip in there i would like to leave that in there versus this eprom all right the original chips in will this thing give us the basic screen look at that it is working so i guess just sort of tweaking the pins with the needle nose did the trick in fact uh what i should do is turn it on and bang it around a little bit it's like my bang test is what i call this uh okay froze so that may well be i'm gonna take the keyboard loop back off though because that was actually on there it shouldn't be no okay so it froze as soon as i did that and i'm pretty sure that is because this chip is just not making good contact anymore in this socket with the eeprom back in i should be able to bang this thing around without it freezing no freezing it is working okay well that's a bummer so this chip is good i should put a check mark on it because it won't work in this machine but it's going to work in something else so that's that is a good chip so there we go one working basket case of a board with burn marks on it this thing is a survivor and i have to say this was a good lesson to show that even though the diagnostic cartridge said the pla was bad it really wasn't it was just that rom not getting selected properly causing that error i can almost guarantee you if i take this rom chip out of this board and we run the diagnostic again it's going to blame the pla again and say the pla is bad let's just let's do that as a final test here there it is pla test bad and that's fake the problem is the rom is not selecting or it's out of the machine or whatever all right so the final thing for this board is a label on this eeprom there it is because you know people don't like it when i leave the window exposed and might as well put this on with the original commodore part there we have it one repaired 64c shortboard and the pal version which here in the united states not super common a huge thanks to henning for sending in all of these boards for me to fix of course i have more down there to get to but i think this will be enough for this video and as you saw trying to repair boards that other people have already repaired before you if they aren't so skilled at removing chips can be really difficult really have to wonder how the back of this board got so burned what kind of heat was being used that did this the board is wavy under my finger here both there on that burn feels like it's delaminating also here under the chip so i do have to wonder what was really wrong with this board um assuming it was just a character rom that failed originally and once the board was butchered and not working properly then the ram was taken and whatever other chips and stuff were taken but otherwise as usual 64 seaboards very reliable so i hope you found this video interesting in some way and if you did 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 and don't forget to check out the second channel there's tons of cool interesting videos over there and of course i want to thank my patrons their names are scrolling up the side of the screen if you want to become a patron you can do so at the link in the description below and i guess that's going to be that so stay healthy stay safe and i'll see you next time bye [Music]

Channel: Adrian's Digital Basement

Views: 75,185

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Id: Ilksm_vjku4

Length: 40min 17sec (2417 seconds)

Published: Sat Jan 15 2022