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Commodore 64 dead + Strange on board voltage

commodore 64 commodore commodore repair

2 replies to this topic

#1 NintariBoi OFFLINE  


    Combat Commando

  • 2 posts

Posted Fri Dec 21, 2018 6:14 PM

So, I recently got a Commodore 64 from one of my neighbors along with a 1541 disk drive, Commodore 1701 monitor, and I found a psu for it at a local vintage video game store. I tested the psu and the 9v and the 5v lines are working. So, I plugged it in the Commodore 64 and turned it on. The LED did not turn on and the screen was a solid black color. I took a look inside and everything looked visually okay. So, next I poked around with my multimeter and found only 1 volt on the cassette port. I know the 5 volt line makes it to the board because I measured the voltage on the power switch and the input and output voltages were 5 volts. So, I let it sit for about 3-4 minutes and then checked the voltage again. For some reason, the on board voltage was at a healthy 5 volts, but the screen remained a solid black color. I don't know what to do at this point. Could it be a bad capacitor, chip, voltage regulator, or something else?


--Other info--

Board Revision: B

Using RF output for the display

Z key missing :(


Thank you.


#2 carlsson OFFLINE  


    Metagalactic Mule

  • 8,965 posts
  • Location:Västerås, Sweden

Posted Fri Dec 21, 2018 6:18 PM

One of the absolutely most common faults on those, besides a malfunctioning power supply, is that PLA chip which acts like a memory controller is broken. You can get reprogrammed parts or modern replacement solutions like PLAnkton, realPLA and a bunch more. However I'm not sure if a broken PLA chip would give symptoms such as voltage drops.

#3 NintariBoi OFFLINE  


    Combat Commando

  • Topic Starter
  • 2 posts

Posted Fri Dec 21, 2018 6:27 PM

Okay, thank you! I'll look into getting a new PLA chip!

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