Commodore 64 SX blank screen on power on

[7800fan]

Disk drive spins up and LED comes on for about 2 seconds then shuts off so the drive seems normal. The screen however is a solid blank and I tried a blind typing trick, nothing worked BUT I can't tell if I have bad keyboard or not.

 

I couldn't find any unusually warm chip after several minutes but I can't check those mounted on the bottom, there isn't much room at all. The CPU, PLA, and the bottom 4 RAM are the hardest for me to check and I don't think I can completely dismantle this to check all the chips.

 

I did try my laser temp probe but I don't think it's accurate in tight space, it kept jumping all over from 70F to 120F even if the laser didn't move. I think I need a different probe to check for this.

 

At present I only have a 64C that I could steal parts, and there isn't many I could steal. 64C used different PLA by combining a couple parts, uses 64kx4 rather than 64kx1, and the SID are incompatible. I think CPU is also a bit different. The CIA (one of it), VIA, and all the ROM chips aren't socketed so it's a risk to ruin a working 64C for parts just to check the SX.

[carlsson]

The SX-64 has an external video output, same pinout as your run of the mill C64. I would suggest you plug in a different monitor there to see if you get any action.