Vic 20 video problem - help please

[+eebuckeye]

I bought a 'tested' Vic 20 from eBay and it is in excellent physical shape, however, I have a problem when I use it. I first connected it with RF and could not get a picture so I ordered these composite video cables: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=281319129631

 

The picture is perfect with these cables for about 10 minutes when the Vic 20 is powered on then the screen gets garbled and goes black.

 

Any suggestions? Is the cable I bought ok? Seems like it is because it works for awhile? Why would it be ok for awhile? The power supply does not seem overly hot nor does the computer.

 

Thank you!

[karokoenig]

*bump*

 

Funny you mention this. I have a similar problem with an old NES I pulled out of a pile of scrap metal on a flea market. At first, the picture is quite good, and after a few minutes, it goes down the drain. You experts out there: Could that be a weak capacitator or something?

[+Random Terrain]

I wonder if any of these links would be useful:

 

vintage-computer.com/vcforum/showthread.php?32692-vic-20-issues&p=249268#post249268

 

sleepingelephant.com/ipw-web/bulletin/bb/viewtopic.php?p=5489&sid=a997907c15cc9ea180aedcb265489180#p5489

 

lemon64.com/forum/viewtopic.php?p=522230&sid=da66d3dab2503a20499975e379903346#522230

[zylon]

I bought a 'tested' Vic 20 from eBay and it is in excellent physical shape, however, I have a problem when I use it. I first connected it with RF and could not get a picture so I ordered these composite video cables: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=281319129631

 

The picture is perfect with these cables for about 10 minutes when the Vic 20 is powered on then the screen gets garbled and goes black.

 

Any suggestions? Is the cable I bought ok? Seems like it is because it works for awhile? Why would it be ok for awhile? The power supply does not seem overly hot nor does the computer.

 

Thank you!

Is it one of the later versions with the round DIN power supply? Sounds like a regulator issue...

[+eebuckeye]

It is a later version Vic20 (rainbow logo) with a round DIN connector for the power supply. Are there any other power supplies I could try from another Commodore computer? How else could I determine the problem?

 

Thanks!

[zylon]

http://www.classiccmp.org/dunfield/vic20/v20diag.txt

 

I believe your RAM may be failing, or at least the internal regulator on the power supply. Are you using carts or tapes when this happens? A way to check this is to use a tape game that will run on unexpanded VIC, but use a 3k minimum RAM cart.

If you're only using carts, I have a console here that has bad ROM and only works with carts. Same version as yours. I could let it go very cheaply since I have another spare.

Those 2nd version ones are not great for long play time with the C64 brick. The VIC actually uses more power than provided by the C64 unit. I use one as a tester for those power supplies. Bad ones will either not start a VIC (black screen), or take time to "warm up".

Edited May 1, 2014 by zylon

[+eebuckeye]

I verified the power supply works great with another vic 20 so it has to be something internal.. Carts do not really work at all and the screen goes bad in about 10 minutes just using basic.

[carlsson]

Hm, it sounds remotely familiar but I can't pinpoint it. I may have read about something similar many years ago on the Denial forum, but it is a bleak reference if you don't know anything particular to search for.

 

It reminds me that I gave away a VIC-20 with a possibly broken 7406, meaning everything but floppy drive access works (6522 replaced without any difference).

[zylon]

I verified the power supply works great with another vic 20 so it has to be something internal.. Carts do not really work at all and the screen goes bad in about 10 minutes just using basic.

RAM or the processor itself. Parts for these are getting very scarce these days. I did get another one of these later decks in. It works well but case is very "yellowed".

[TheRealAnubis]

I know that the video IC in the early Vic's (and possibly the later ones) isn't heatsinked to the metal box that it's in (the C64 has a copper finger that goes from the IC top to the metal lid). I took apart an old Vic 20 a while back and the IC was disintegrating inside that box - after running it for about 20 minutes I checked it out for heat and it was pretty hot. I popped on a few copper heatsinks with the thermal tape that attaches them to the top of the IC to help dissipate that heat. If nothing else works, it's worth a shot - also, if you can, try swapping out the VIC chip in there to see if that makes a difference.

Good luck!

 

Here are picture of a different Vic, but even the edge on this video IC was flaking off..

 

 

Edited June 26, 2014 by TheRealAnubis

[channelmaniac]

Buy a can of "air", turn it upside down, and spray the liquid on 1 chip at a time to see which one magically starts working again when cooled off.

 

Add a heatsink to it or replace it.

[TheRealAnubis]

Buy a can of "air", turn it upside down, and spray the liquid on 1 chip at a time to see which one magically starts working again when cooled off.

 

Add a heatsink to it or replace it.

 

I've heard of that, but never tried it! That and 'piggybacking' RAM to locate the faulty IC. I've tried that over a dozen times, and finally while tinkering with a C64 it finally worked! I was surprised (and impressed!). I'll give your idea a try as well - once they're sick, there's not much to lose!