Troubleshooting An Original C64, 326298 REV A Board

[codesurfer.dev]

I have never owned a C64 before, but just acquired one from my neighbor to evaluate and possibly purchase (Serial # S00067211). I have been getting more and more into retro computer tinkering and modding, and I started blogging about my projects at https://blog.codesurfer.dev

 

I opened the case to test the electrolytic capacitors before powering it up (I also tested the power supply separately), and noticed that all of the ICs are dated 1982 with the possible exception of the PLA, the sticker on it reads "C64 REV 3 8411". Does that mean that the PLA is a 1984 version? Is this a particularly unique/rare version of C64 with collector value, and should I avoid doing any mods on it?

 

A few interesting things happened when I originally powered this unit up. Firstly, even with the power switch in the "OFF" position, when I connected the power supply to the computer and then plugged the power supply into the outlet, the "POWER" LED came on! Secondly, my monitor registered a signal (the "no signal" prompt went away) but it was the "black screen" that I have read so much about. Needless to say this was bittersweet, I was hoping to see something come up on the screen, but figured, "now I can learn & blog about this C64 while troubleshooting it".

 

I downloaded a copy of the C64 Service Manual from The Internet Archive, and checking the board schematic saw that the POWER LED should only turn on when the main +5VDC is available. The schematic showed that the power switch interrupts the +5VDC coming from the power brick, and one leg of the 9VAC supplying the other voltages on the board. So I opened it up again, but this time removed the board from the bottom case half and tested the DPDT (Double Pole Double Throw) power switch with my multimeter. The switch checked out just fine, so before re-assembling it I connected the POWER LED and then the power brick. This time the LED did not come on until I turned on the power switch! Seeing that I decided to connect the monitor using my DIY Atari 800 A/V cable (The 5 pin DIN pinouts of the C64 and Atari 800 are similar enough to make this possible) and I got a clean yet monochrome screen!!!

 

Has anyone else experienced something like this? I am thinking about looking for short circuits under the RF shielding before re-assembly. Any advice from the forum is greatly appreciated.

[ballyalley]

"odesurfer.dev" pointed me to this thread and asked me:

 

"I know you are into the Astrocade, but do you have any knowledge/experience with the C64?

 

"I just posted in the commodore 8 bit section of the atariage forums my experiences so far with a C64 that I got from my neighbor. Do you or anyone in your network have experience with C64’s that I could pick their brains?"

 

I figured that I would answer him here.  I don't have any suggestions about what your hardware problem.  If you don't get any response there, then try the Lemon64 website:

 

https://www.lemon64.com/

 

There will be people falling over themselves to help you in those C64 forums.

 

As to your question: yeah, I know about the C64.  It was my first computer.  I had it from around 1984-1986, and then I replaced it with a C128, which I ran nearly always in C64 mode until 1989/90, when I sold it.  During that time, my C64 had to have parts replaced on numerous occasions.  I'm not surprised to hear your having issues.  Then again, it's to be expected.  The computer is 40 years old!

 

Over the years, I've had a few Commodore 64 computers, but I don't have any now.  A couple of months back, Carl (from the TS2068 group) brought along his newly-acquired C64 when we had a Timex Day here at my place with Ryan.  He had no accessories, but I still had a 1571 in the garage and we loaded and played some games on it.

 

My buddy Brian bought a C64 Mini in 2022 and we covered it on his YouTube channel in a video.  You might get something out of that video; general knowledge, at least:

 

 

There is a sort-of part two to the video as well:

 

A few years ago my friend Chris and I played a popular game on the C64 using emulation:

 

If you visit my Orphaned Computer & Games website, then you'll find it has articles about the Commodore 64 in random places.  My website is here:

 

https://orphanedgames.com/

 

When Carl and Ryan were here, we played some C64 games that my buddy Chris wrote in the late 1990s/early-2000s.  You can find disk images of them here:

 

https://orphanedgames.com/c64.htm

 

Give all four of 'em a try.  "Super Space Carnage" thrilled both Carl and Ryan.  It's not what you expect.

 

One of my earliest c64 articles covers GEOS and it dates back to 1994 (!).  Oh, boy, I'm getting old:

 

https://orphanedgames.com/ocgs/Vol_I_Issue_1/ocgs_vol_I_issue_1_(June_1994)(GEOS_and_Commodore).html

 

Have fun with the C64.  You'll get it going!

 

Adam

 

[carlsson]

How many pins does the video connector have? The first revision only has 5 pins, slightly newer have 8 pins. I would think it outputs color composite video, rather than only luminance unless something is bad or the machine is of a different video standard than your monitor. What is the model number of the VIC-II chip?

[codesurfer.dev]

Hello Anders, It is the five pin DIN A/V, a 326298 REV A of the circuit board. The VIC-II is a 6567R5 dated the forty third week of 1982 (photo of my VIC-II chip attached).

[carlsson]

You might have some use of going through Ray Carlsen's documents: https://portcommodore.com/rcarlsen/cbm/c64/

[codesurfer.dev]

I will do that, thank you Anders. Do you know if this configuration of C64 is anything special/unique? Serial # S00067211. I like to mod my computers and tinker with them, but I would not tamper with a computer that is rare or has collector value in it's original condition.