I have a Vic 20 I got complete in box with a few games for $20.
It powers up, but no video on TV or Commodore monitor.

Is there a was I can test the socket with a multimeter?
And do you guys have any suggestions on how to fix it?

Thank You!!!

Have you checked whether it is on the right channel and verify that the video cable may be damaged.
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Are you connected to your TV through the modulator?

Yes I have checked these things. Correct channel, I figured my modulator was bad so I plugged it in to my 64 monitor. Still no video. I haven't tried plugging in the modulator to the 64 and bringing that up on to tv. Either way I think the Vic chip in Vic-20 is bad.

Don't try it on the C64...

VIC20 video port:

C64 video port:


As you can see there's no +6V on pin 1...

If you hook it to a monitor only the composite video + audio works, not a chroma + luma + audio hookup.


Anyway, what PSU does the VIC20 have, two prong or the same type as the C64?

How do you know it powers up, LED goes on, anything else? Does a datassette start if you push SHIFT and RUN/STOP? Does a diskdrive start if you type LOAD"$",8 ?

The LED comes on, I haven't tried loading a disk with it yet. This is why I asked. You guys have more knowledge than me on this stuff. Thanks for the help, I appreciate it. I'll try these steps and let you know. Thanks!!!

It has the two prong PSU.

Then there's probably not anything wrong with the PSU, the two prong version is very sturdy.

If you can't wait to get in there and check you may want to try reseating socketed chips, check electrolytic caps for leakage, see if anything looks burnt...

Only problem I've had with a VIC-20 was that one of the roms broke, I just got a black screen.

Quote:

UE12 901486-06 ROM KERNAL Blank screen on startup, no drive access, game carts don't work. Partial failure: some game carts may still work.

I was going to burn a rom for it but as I have two others I haven't bothered to fix it yet. It was the only circuit in a socket in that machine so it's possible it has been replaced once before.

You can take a peek on Ray's information here:
http://personalpages.tds.net/~rcarlsen/cbm/vic20/

I have re-seated chips, and checked for bad capacitors. None leaking.
Nothing looks burnt or out of the ordinary. So I'm guessing the one ROM possibly broke? Is there any place that I can get a replacement?
Would it be better if I replaced all the socketed chips?
I know some of these questions may annoy some of you and I apologize. I am very interested in learning how to fix and use these machines. I can get around on my C=64 pretty well. i just figured that I have the Vic-20 and I payed $20 for it I may as well fix it, or at least try to.

Thanks!!!

If you have chips in sockets, it's at least easier to swap the chips. The sockets themselves are sometimes the reason for the troubles.

It would be easiest if you had another one to swap chips with, if you don't have any measuring instruments (like oscilloscope or frequency counter) or idea about it then there's not much to do but try and swap chips.

Did you try and hook up composite video to pin 4 and gnd on pin 2? No reason to start fiddling with the electronics if the hookup isn't right.
The RF modules fail sometimes, I have one broken myself, so it's not a major surprise if you're not getting picture from that.

The reset circuit could be acting up, it holds the reset line for a short while when starting up. If there's something wrong with the CPU or its clock this would also cause this kind of problem.

If you look at Ray's document
http://personalpages.tds.net/~.../vic20.txt
... you have these alternatives:

Quote:

UAB1 6522 VIA INTERFACE, KEYBOARD-SERIAL Startup screen normal, but no cursor. Keyboard doesn't work at all. Partial failure: some keys "stuck" or don't work... may be a whole row or column. Also can cause serial port (drive access) problems. Can produce blank screen if shorted (remove to check). UAB3 6522 VIA INTERFACE, SERIAL-JOY-USER-CASS Startup screen normal, but drive access problems ("SEARCHING FOR.. " forever). One or more joystick positions don't work. No cassette or user port access. Can produce blank screen if shorted (remove to check). UB6 LM555 TIMER POWER-ON SYSTEM RESET Will not reset on power up. May produce garbled or random screen characters-graphics, or screen may start up "frozen". If drive resets when computer is powered up, this chip is OK. UB7 6560-101 VIC VIDEO/AUDIO White or blank screen, garbled or no video, screen full of (or few random) "garbage" characters. "Blind" disk commands may still work. Partial failure: Dark or smeary image, loss of color, garbled or no sound, game paddles or light pen doesn't work. UC4 74LS138 LOGIC MEMORY CONTROL Blank screen. UC5 74LS138 LOGIC BLOCK CONTROL Blank screen. UD2-UD6 UE1-UE6 2114 or TMM314A RAM MEMORY Blank screen. Partial failure: less than normal "3583 BYTES FREE" at startup, sometimes will produce "garbage" screen or screen freeze after warmup. Shorted chips may get very hot. UD8 and UE8 MPS65245 or MOS65245 or 74LS245 TRI-STATE LOGIC Blank screen. Partical failure: garbled video or audio. see UB7 UE10 6502 MICROPROCESSOR Blank screen. Partial failure: computer may run for awhile, then freeze. UE12 901486-06 ROM KERNAL Blank screen on startup, no drive access, game carts don't work. Partial failure: games may still work. UF8 MPS65245 or MOS65245 or 74LS245 TRI-STATE LOGIC Blank screen.

I don't have a whole lot of experience myself with VIC-20, I've repaired a few, it has been the Kernal, UF8 and a RAM memory. When it comes to those logic chips it can be difficult to check, I just swapped to see if there was any difference and finally found the one that was broken.

RAM chips are a common source of error, I think Murphy's Law clearly states that it's not likely it's one of those chips that easily swaps that are faulty - but why not try that first.

I usually check eBay before buying components elsewhere, perhaps Denial is a good place to ask:
http://sleepingelephant.com/denial/

Searching the chip number in google sometimes helps as well.

Is it an NTSC or PAL machine?
I think I mistakenly bought an NTSC kernal not long ago, maybe you could try that (NTSC: 901486-06, PAL 901486-07).

It is an NTSC machine. I'll take a look on sleeping elephant.
Thanks alot!

I've had the majority of bad vics that I've fixed with bad kernal roms.
Followed second by the VIC chip itself, with ram a distant third.


Later,
dabone

I'll see if I can order the chips. And Ill try them. I figure if I'm going to use it I may as well eliminate as many things that can go bad before they do.

Thanks for the tips!

Where are you located?

Later,
dabone

I'm located in Rome, NY.