Commodore 64C with a frustratingly simple fault 

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

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.

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.

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.

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

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

cool stuff another C64 saved from the landfill

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

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.

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.

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

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

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

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

Great vídeo CRG

Happy hello everyone. Like butten activated

Great fix! Very satisfying 🎉

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.

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.

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

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

Excelente vídeo. Parabéns e obrigado!

Great watch

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

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.

Good Job!

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

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.

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

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!

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.

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

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

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

You accent is awesome!

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

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

I LOVE C64❤❤ FOREVER ❤❤❤❤

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

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

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

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

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 😢😢

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?