Blank screen c64 ICs are all good, now what?

[vthyng]

I am repairing a 250425 board that I have socketed all of the chips and confirmed through trying them in another working board that they are all good. The problem is a blank screen almost 100% of the time. On 2 or 3 occasions while probing around with an oscilloscope the screen has started working, albeit messed up characters on the screen. It appears that the RDY signal is never getting set low by the vic chip for the CPU to be given time to run (suspect VIC, but it is tested good), and several of the chip enable signals never go low (suspect the PLA, but it has been tested good). Today when the board was in a rare state of showing something on the screen I checked the RDY signal and other chip enable signals and they all seemed to be working correctly.

So what do I check next? 5V and 12V off the regulators are good. Do I check capacitors around the VIC? There are no blown capacitors anywhere on the board that I can see.

Thanks for any guidance you have,

Vince

 

[Ruud]

Bad contact with the socket, bad solder point, bad crystal, broken line(s). You see, still enough things that can go bad. And I have seen them all! (OK, luckily not all on the same board )

 

[vthyng]

Ugh, I thought I had tested RAM, but 2 chips were bad. All better now!