Picked up a Vic from Kijiji, seller said it powered on and booted. I wanted to make sure so when I got to the seller's place I hooked it up to a mini crt and got red power led and a black screen. Offered $20 on the chance I could fix it and took it home. It's the 2 pin psu so an earlier revision, I had a Vic as a kid and I'm dying to get this bad boy going again. I read a great post at this link: http://personalpages.tds.net/~rcarlsen/ ... /vic20.txt
and it was pretty helpful. I did the am radio check and I'm hearing the rf interference Mr. Carlsen describes - a good sign. Tested the AC output of the psu with a multimeter and it read appx 10.4 volts and although the psu is supposed to be 9V I saw a spec sheet that said my psu (902502-02) is rated for 10V output so maybe that is within spec? I'm handy with a soldering iron and have a very basic knowledge of using multimeters but after reading a bunch of info online I feel seriously out of my depth here. I could perhaps strip down to the pcb and try reseating all of the socketed chips maybe... somehow I sort of doubt it could be that simple. I have a small feeling the problem is the Vic chip (6560-101 or 6561-101) due to some of the behavior and the fact that it's a common problem, but odds are I have no real idea whatsoever. Also not too much of an idea of where to start. Any help or suggestions would be super appreciated and forgive my newbie-ness, I just want to fix the stuff man! I've had a lot of luck with old cartridge consoles but this is a whole 'nother level...
10.4 volt sounds perfect. Now you can check that you have around 5 volts DC inside aswell. Look at the cassette interface (google it) and it should have a +5V pin and GND pin. You should see around 4.5-5.5 volt accross that. If not, the regulator could be broken.
There are a number of things that could be wrong with black screens. The 6560 is one, but sometimes there are other things that also lead to black screens (other IC's or traces being broken). Look for signs of damage on the PCB (both sides).
Do you have a cartridge game or alike? Try booting the Vic-20 with the cart to see if it reacts differently (e.g. not a black screen).
Do you have a tape or disk drive? If so, try typing LOAD (+RETURN key) to see if the tape starts/stops (it should stop if you press "RUN/STOP" key after starting the tape (e.g. with play pressed on tape)). If you have a disk drive try typing "LOAD"$",8 (+RETURN key) to see if the disk drive is accessed.
Other than that, you will have to start testing IC's by swapping them from a working Vic-20... Please note that its easy to bend legs if you take one out/insert it back into a socket. Its almost impossible to see. You could look for such bent legs if you have socketed chips (and the previous owner has tried to take them out/in and bent a leg).
If you have an oscilloscope, you could try to look for reset signal, activity on the address bus (A0 line on expansion port) and so on.. but its a longer route.