VIC-20 black screen - what do check/replace first ?

[Overdoc]

I've got about 10 or 15 VIC-20 but 4 of the are dead and produce a 'black screen of death'.
I have already done the known checks like e.g. fuse check, reset check, cartridge check, blind load comands, heat check on chips, etc., but to no luck

I have repaired tons of C64 and the C64 is known for a rather high PLA chip failure.
Now, which chip would you desolder and replace first ?
Jogi once told me every VIC-20 will produce a empty border screen if only the VIC is still in the board, but that would mean a lot of desoldering

Does the VIC die often ? Or do the rams fail more often ? Or the CPU ? (it doesn't fail often in the C64, btw.) The kernel is socketed on some of them, so this one can be ruled out on 3 of the 4, I think.

Thanx for any repair suggestions !

[6502dude]

Try swapping the 6560/6561 chip.

It is prone to failure and will result in no video if it fails.

[eslapion]

... Does the VIC die often ?

Yes it does and the main cause is exposure to high temperatures for extended periods of time. All it takes to prevent that is a small heat sink...

[Iltanen]

Eslapion, you got me worried since my VIC is often on for over 24 hours.. could that be dangerous? I think not, since when my dad used to do distillation with it, it was on for more than a week

[Jeff-20]

distillation?

[6502dude]

distillation?

Either purifying water or making booze?

For what it's worth, the video chip does tend to run hot and a heat sink may help. However there are many Vic-20s out there that have run for many years without a heatsink on their video chip.

I had one Vic-20 run for a couple of years on 7x24 basis running a "homebrew" house alarm system.

During MegaCart testing, I have had Vic-20 on for weeks at a time and have yet to have a 6560 fail on me.

[Iltanen]

Yup, it's in the "Serious scientific applications" thread. It takes a week and a well optimized program (many tries to get the values right) to get to 94 %vol. The biggest cause of inaccuracy is that the voltage varies from 220 to 230 or something like that.

Many VICs got a broken AD converter when doing that, it's the long data cord which causes some peaks.. eslapion knows these things. It should be optically separated but it was never done.