Commodore 64C with a frustratingly simple fault

Its been a while since we looked at a faulty C64 and this 64C is certainly one of them. What turns out to be a rather simple fix in the end was nothing short of frustrating and took me on a wild goose chase of looking for problems where there were none. All part of the fun though so join me as we dig into this machine and try to figure out why its not working!
Follow CRG on twitter / yt_crg

[@c128stuff]

Lack of 9VAC will cause timers to fail because its 50hz (or 60 on ntsc machines) line frequency is used to generate the pulse counted by the CIA counters. That is also why there is ac power there at all.

[@CRG]

Thanks for letting me know. Probably should have known that already 😉

[@ThereIsOnly1ArcNinja]

Nice fix. I've had a C64C showing quite similar behavior - just add some character rainbowing and sparkling - back in the mid 90's with no internet, no test harness or even cartridge to find help. Drove me crazy for weeks until I've found the cause - an intermittent mechanical failure in the power distribution around the fuse. By than I've had swapped out the fuse, both CIAs, the VIC, the CPU, the Kernal and the Combo Chip with known good parts.🤯 What that taught me: Don't freak out if your C64 freaks out. Some mild percussive maintenance may guide you to the cause! 😁 So I could feel your frustration chasing those loose electrons falling out of this board.

[@CRG]

Thanks. Never heard of a power issue causing flickering like that so good to know. Its easy sometimes to fall into the trap of chasing a faulty component when actually is a physical break somewhere on the board.

[@Hounddoggy33]

Great job! Glad you didn't give up on this one!

[@CRG]

Thanks, it did take me on a bit of a ride but happy it got there in the end.

[@Hounddoggy33]

@@CRG You on holiday?

[@CRG]

@@Hounddoggy33 No, the past couple of months have been very busy with work and DIY in the house. Hoping to get back to videos over Easter. Thanks for asking.

[@jarnailbrar6732]

That is so much work, you have so much patience. Glad to see you got it fixed.

[@MrFixiit]

cool stuff another C64 saved from the landfill

[@CRG]

Thanks

[@Plan-C]

Enjoyed that thanks. Nice work! Really thought you had it there after the broken trace. Wsn't expecting the blown fuse on top.

[@CRG]

At least that was easier to fix 😂

[@YogSothoth1969]

Very interessting, glad you got it running in the end, thanks for sharing!!! Greetings, Michael (o7 Commander ;-)

[@CRG]

I really need to get back into Elite 🙂

[@PJBonoVox]

Hope you're well dude. It's been a long time in KZbin land since your last video.

[@CRG]

It has been a long time but all is well, thanks for asking. I've been doing a lot of work around the house, we got a new kitchen and it's taken most all my spare time. That's done now so next job is a redress of the man cave then I'll be back to videos. All being well I'll be back next week.

[@42markk42]

@@CRG So that didn't go to plan .... Hope to see you back soon 👍

[@CRG]

@@42markk42 things rarely go to plan, in fact the past few weeks have been very busy with work and family stuff. But the work in the man cave is all done so all being well videos will return next week.

[@wimwiddershins]

Nice one! Another C64c back in the game. :)

[@CRG]

I'm just happy it worked out in the end.

[@Ghost82uk]

Just to answer your question mate, the system clock is calculated by the mains frequently, meaning if you don't have the 9v AC you don't get the clock

[@CRG]

Thanks for letting me know 👍

[@jeffreyphipps1507]

Wouldn't be a C-64 if it didn't have a set of odd issues combining into something you hadn't seen before.

[@CRG]

This is true, all part of the fun though!

[@philb2831]

Really like you video I like how you explained your thought process. Liked and subbed Where do you get your spares from?

[@CRG]

Sorry for the late reply but for spare parts I always try www.retroleum.co.uk/ first. Always hold a decent stock of parts and at a reasonable price!

[@peterbilt3385]

Really enjoyed this. I don't have the repair skills or kit to diagnose, but I do have 2 recently acquired working breadbins and would very much appreciate if anyone knows of someone trustworthy the UK who would be able to repair my c64's for a reasonable price if I have issues?

[@CRG]

I would recommend joining one of the user groups on the likes of facebook or perhaps discord. There's loads of people out there who would happily get you up an running again should one of the machines fail. One common source of failure though is the power supply. When they go bad the 5V line can go very high frying various components (usually the ram goes first). You might have noticed that inline with my power supply I am using a power saver which is designed to cut the power as soon as the 5V goes above 5.2 (I think might be 5.3). I'd highly recommend either getting one of those or one of the new power supplies.

[@peterbilt3385]

@CRG Thank you very much. I don't use Facebook, but I have already purchased one of those Electroware replacement PSU's from Poland yesterday (new revision) which sound ok and won't be using the original ones again!

[@dr.ignacioglez.9677]

I LOVE C64❤❤ FOREVER ❤❤❤❤

[@CRG]

Hard to beat a Commdore 64, it is a lovely system and they are always a pleasure to work on.

[@Wikcentral]

The missing LED is signs of blown fuse, the fuse can blow sometimes with plugging into cassette port with power on or problem with cassette drive. The 9vac is needed for the CIA TOD clock, which drives the times on the diagnostic test. That was a fun fix.

[@CRG]

Thanks for clarifying the 9v requirement for the TOD clock. Not sure how the fuse went but maybe hot plugging the cassette deck as you said.

[@doktor6495]

The CIAs need the 9VAC to generate the TOD (TimeOfDay) out of the 50/60 Hz. Greetings, Doc64!

[@CRG]

That explains why there was no clock then. Thanks for clarifying 👍

[@morantaylor]

9v line gets rectified and provides a 50/60 Hz square wave used for RTC clock.

[@CRG]

Thanks for letting me know.

[@Shmbler]

A quite interesting fault. Nice to see how the symptoms (dead card slot and random row 0 keys) all made sense in the end. We've all learned to keep looking for common connections of failng components even if it seems they are not related at all. I wonder if the "magic finger" method would have worked here just as it did for me several times when there were floating inputs due to broken traces. I would have expected that simply touching the broken data line (CPU side) with a fingertip would have changed the random key presses significantly.

[@CRG]

Looking back at it now I probably should have noticed on the keyboard connector that the pin wasn't fully low, there was some noise on it and probably an indication that it was floating. While not in the video I scoped the databus at the CPU and when it looked fine there I didn't bother looking at it on the CIA or the cartridge port. Even doing that would have pointed to the fault straight away. Easy to say all that in hindsight though. I'm just glad it got fixed in the end even if it did take me on a ride 😁

[@c128stuff]

@@CRG thanks for sharing that ride :-)

[@Flashy7]

What a fault, that trace did not look that bad at all, I think it was everybody else's last suspect, too...

[@CRG]

It certainly didn't look broken, even looking under the highest magnification I have I can't see the damage. Must just have been a hairline fracture of the copper.

[@DaveVelociraptor]

The random characters appearing are classic signs of a haunted commodore.

[@CRG]

Didn't help me much on the lottery though :)

[@Tjuwantjutju]

Happy hello everyone. Like butten activated

[@CRG]

Thanks

[@dorianbussenius8501]

As good as the Diag cart is I have seen it miss problems easily, I just did a C64 breadbin with an issue of fastload carts not working and normal loading results in mostly failed loading. Diag said both CIA were OK, I tested them with a tester that test the CIA chips and yeah one was actually bad on Channel A... if I swapped them then the Diag cart finds the bad CIA but otherway round... so yeah Diag cart can lead you in the wrong direction..... Corrosion... does more damage than it looks.. good repair!

[@CRG]

I think its possible that a partly faulty CIA may work in one position and not the others, fairly sure I've read that somewhere before. I suppose in your case the chip was still working in terms of passing the diag test but had a failure elsewhere. I was surprised that the corrosion damaged the trace as it did. I can't see the break so it must just be a hairline crack. Perhaps whatever that was split on the board while corroding the surface stressed the copper cracking it.

[@dorianbussenius8501]

@@CRG Since there were scratches on the board I would say someone was chasing the original issue of the blown fuse (no audio) the color ram probably died from sitting around, seen that heaps... the corrosion was probably drink or repair fluid spilt while over the board.... amazing how the faults pile up and your chasing more than one thanks to bad handling

[@cthlhu]

Another great video! Glad you were able to bring this one back to life.

[@CRG]

Thanks

[@fra4455]

Great vídeo CRG

[@CRG]

Thanks

[@darrenjkendall]

Might have to send you my 64 so you can work your wizardry on it, when i connect it to power and video it just doesn't do anything anymore 😢😢

[@micflynn1]

You missed that the joystick ports are also connected to the keyboard port 1012 goes to the joystick Port you could have a shorted capacitor a shorted resistor I'm short between pins so you should look at your schematics a little closer before you jump to the soldering chips not saying that it was wrong but it might have saved you some trouble

[@nickolasgaspar9660]

The issues might appear to be silly but they were really tricky. I also have a C64c with unexplained surface corrosion something that I don't find on other 8bit machines.

[@Gilerajohannes]

I think that Pla on the "new" model is called super pla, I have newer seen a super pla go bad only the old model pla, but at first look on the screen it looks like a bad pla but if I remember right then the whole screen woud be filled with lethers and numbers and symbols when it's powered on, I have repaird some commodore c64 bords but with the old model pla the later ons are in the Commodore c64g or in c64c slimline model like the one in the video, but in 2010 I had to sell my collection of Commodore 64ers and Amiga's it's a long story but can say one thing bad economy and no job at that time, and had a bad sholder joint problem but im ok now and got a good job now, but my Commodore 64 days are gone, the worst thing is that I took no image backup of my floppy discs that hurts a bit

[@0toleranz]

It would de interesting to see what traces were affected by the corrosion. Maybe the one of them carried the 9 volts to the CIAs and also to the color ram and killed it and blew the fuse in the process. It’s just a wild guess but you never know. Nice fix though - been fun to watch.

[@Kerveros1904]

The first and original Matrix number generator effect before the movie appears. Maybe it is the proof that the Matrix exists.

[@paulspark7287]

Isn't that similar to what happens when you wiggle the joystick in port 1?

[@QunMang]

For the game selection to test the sound, my eye was on Donkey Kong thinking of an 8-bit dance party. Different channel though, and probably not even the right Donkey Kong. Good work though.

[@CRG]

That is the same Donkey Kong and while I do enjoy a good 8 bit dance party that's Adrian's thing plus that tune from Last Ninja 3 is fantastic and I hadn't heard it in a while.

[@QunMang]

@@CRG I stand corrected, and you are right- that LN3 tune is great.

[@JosepsGSX]

Keep that style of music and that 5% outro viewers might go up a bit. Can´t say about the image thought, I have no sense of aesthetics, but you can´t go wrong with those soundtracks. Superb subtitle work here. The whole ride documented this way has been quite interesting.

[@CRG]

Thanks, glad you enjoyed the video. I just record as I work, nothing scripted so I tend to stick in the text almost as comment to myself. Hard to beat a bit of SID chip music, my normal outro song is from an Amiga game, prehistoric tale, but I couldn't cut that epic song from last ninja. The new image is something I've had sitting for a few months just not used it yet. I like it but then again my sense of aesthetics are probably a bit wanting too 😂

[@steveaustin4118]

when I do silly thing like this, I just take it as lesson learned and next time look closer

[@christianlarsen1070]

A look at the keyboard matrix reveals that all the characters are related to row 0.

[@deborahberi3249]

Excellent Video which is a perfect example of a non-standard fix or fault. Completely reminds one to stay on their toes when troubleshooting! -Mark.

[@CRG]

Absolutely, its not always going to be a failed component although granted a damaged trace like that bound to be a rare thing.

[@renepedersen7141]

Broken trace can be hard to find. I really like repair videos, thanks :)

[@CRG]

Thank you for watching. Plenty of other stuff piled high here waiting repair so hopefully something that will interest you in the future too.

[@zx85]

Great fix! Very satisfying 🎉

[@safatkhan676]

You accent is awesome!

[@decidedly_retro]

I must admit that as soon as the ROM cartridge didn’t boot I’d have suspected the address and data lines going to the cartridge port rather than the chips. However, hindsight is a wonderful thing.

[@CRG]

It's not in the video but I did check the databus at the CPU and it looked fine but it didn't cross my mind to check same at the expansion. Lesson learnt on my part though, it'll be the first thing I check in any future similar repairs.

[@decidedly_retro]

Yeah, though given that the machine was mostly working but not reading the cartridge I would have started just “listening” to the buses at the cartridge port. That would have probably have flagged up that D0 looked either quiet or just odd, probably floating.

[@FernandoMagaldiCachoeiro]

Excelente vídeo. Parabéns e obrigado!

[@CRG]

Thanks for saying so.

[@inserttanjiromeme5496]

Good Job!

[@IDK-bf9lv]

Great watch

[@SocrateTheCat]

Thank you for this great video but I have a question about a C64C short board. I got the fuse joke. But since I put in a new one, I have the timers of dead test cartridge which works intermittently. (it remains at zero and I have no music). Do you have any idea where I could look? Thank you

[@CRG]

Check if you have 9 volt on the vdd pin of the Sid, top right pin looking at the chip. If that is missing then you have another fault after the fuse. The C64C schematics are easy enough to find online you can follow the 9v rail on that.

[@SocrateTheCat]

@@CRG Thank you for your answer. I found the cause and it's a 2nd joke with the fuse. One of the fuse holder clamps was not tight enough so the fuse was not touching the edges. But visually we couldn't see anything, i found the cause randomly by taking my measurements by pressing the fuse. I tightened the clamp and it's ok now.