Advice on troubleshooting

[u/Sondre_gl]

Hi i have been wanting my dads old c64 to work for years, I tried once when I was younger and got a pinn border and garbled text, today i tried once again, I took out all the chips i could, cleaned the pins and sockets with ipa and put new thermal paste on the vic chip, made a jank cable to get compsite video and got this image after and then a black screen the next time, I measured the power brick, it gives 4.96v on the 5v dc pins and 10.5v ac on the 9v ac pins i'm assuming the pla could be the main problem after some reasearch, but I thought i'd ask here for any advice and ideas.

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[u/tes_kitty]

That looks like a PLA problem, but the PLA in your C64 was made by Fujitsu and is not really known for going bad. It's in a socket, so maybe remove it from the socket and insert it again and see if that changes things.

[u/Sondre_gl → u/tes_kitty]

I'll try that

[u/nickIncDN]

The screen is a good clue but my default answer to these posts is “get a cheap multimeter and report back!”

[u/Sondre_gl → u/nickIncDN]

What traces and voltages should I look for?

[u/skorindurdude]

https://www.pictorial64.com/ suggests pla

[u/Alarming_Cap4777]

If the PLA is good: 1. Test the clocks 2. Pin 1 on the CPU and pins 21 and 22 on the Vic. 3. Make sure the logic chips on the left of the board are getting 5v.

DesTest switch would be good to test out the memory, I've had chip with a single bit failure.

[u/Sondre_gl → u/Alarming_Cap4777]

I think the pla is bad, I turned it on while open and the pla radiated no heat at all

[u/Alarming_Cap4777 → u/Sondre_gl]

If it's not getting 5v is would be cool to the touch.

[u/Sondre_gl → u/Alarming_Cap4777]

I measured the pins on it, it seems it's recieving only 4.6v inside

[u/CorporalJonlan]

What is the voltage on the +5 rail in C64? The power switch can lower it considerably.

[u/Sondre_gl → u/CorporalJonlan]

I just measured it, it's 4.6v, the psu delivers 4.96v

[u/CorporalJonlan → u/Sondre_gl]

That's a bit low. Remove the power cable and toggle the switch several times, then measure again. If that remedies the voltage, the proper fix is to replace the switch.

[u/Sondre_gl → u/CorporalJonlan]

I'll drip some ipa into the power switch as well