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Commodore 64 (black screen with line)

Commodore 64 Commodore 8-bit problem black screen

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#1 Antic OFFLINE  


    Combat Commando

  • 1 posts

Posted Tue Jul 24, 2018 3:02 PM



Im trying to fix this Commodore 64 but so far no success. When I power it up I get a line on screen (look at picture), after about 3 minutes the chips are slowly getting worm except for the PLA,SID and Kernal they get hot but just enough so that they can still be touched, i probed with my scope pins 1 and 39 on cpu and the clock seems fine ,how do I proceed from here   :?


I am suspecting the PLA but dont have another Commodore to test it  


I heard that I could test the chips using a arduino but probably would need a code for that.

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#2 shoestring OFFLINE  



  • 441 posts
  • Location:Sydney

Posted Fri Jul 27, 2018 6:00 PM

Suspect a dead PLA unless proven otherwise.


A dead SID should not prevent a c64 from booting, unless its shorted directly to gnd which may may prevent it from doing so. You'll see a blank screen or sometimes jumbled multicoloured screen.  Pull the SID chip out and see if it boots, a c64 should always boot without one if that's the only fault on the board.


What are your +5v voltages like ?


Since you have a scope.


What does RST ( pin 40 ) do on power up ? ( should toggle from low for half a second and hold high ).

Any activity on the Address and Data pins ?. If they toggle for a short time after cold reset then get stuck ( low or high ).. suspect bad DRAM or mask rom. 

Any DRAM chips get hot to the touch?


Check pin 38( R/W ),

* What is it doing?. This determines what the next DRAM access will be ( Either a read or a write ). A low indicates a write, a high should indicate a read.

* Pin 39 should always be high when a r/w access occurs.

* Are any data pins from the 6510 floating during a write access ? ( r/w low ).

Also tagged with one or more of these keywords: Commodore 64, Commodore, 8-bit, problem, black screen

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