VIC 20 repairs

Overdoc · Post by **Overdoc** » Thu Nov 13, 2008 10:14 am

I had about 5 dead VIC20s from which I recently repaired 4, as well as 2 from other people I repaired at a meeting some days ago.

Now, strange thing is that on all except one of them the kernel or basic roms were dead (one had a bad vic)
I have repaired tons of C64, but in the C64 the roms die in a only very rare case.

Has anyone else made this experience ? Or could it be people often insert/detach carridges without turnng the machine off, and therefore many VICs have dead roms ?

Also, while I am at it:

The one VIC which is not repaired yet has all roms working, as well as a working cpu and working vic.
Now, I suspect bad ram.
Can anyone tell me if the machine would still work if the 6116 rams were dead ?? (with only 1kb, ofcourse)
I think I first want to swap the 2114 rams and then go for other chips. Will also measure the chip-select lines next time, maybe some 74LS138 chips are shot ?

Thanx for any other repair hints !

PaulQ · Post by **PaulQ** » Thu Nov 13, 2008 3:56 pm

This may be of use to you:

http://personalpages.tds.net/~rcarlsen/cbm/vic20.txt

Overdoc · Post by **Overdoc** » Fri Nov 14, 2008 4:09 am

Thanx, DigitalQuirk, I know Ray's tips for years and has helped me quite a lot when I began repairing C64s.
Unfortunately I just get a black screen on this one VIC20, for which could be a lot of chips be responsible, and also Ray thinks if a rma chip is bad it could still come up with the start screen, but not necessarily...
I just thaught maybe there is one chip who is common to fail, just like the PLA in the C64 ?! To have something to start with desoldering ?!
But seems like I already found out myself that it is the ROMs in the VIC20 which like to break down

Clockmeister · Post by **Clockmeister** » Sun Nov 16, 2008 2:16 am

Overdoc wrote:Thanx, DigitalQuirk, I know Ray's tips for years and has helped me quite a lot when I began repairing C64s.
Unfortunately I just get a black screen on this one VIC20, for which could be a lot of chips be responsible, and also Ray thinks if a rma chip is bad it could still come up with the start screen, but not necessarily...
I just thaught maybe there is one chip who is common to fail, just like the PLA in the C64 ?! To have something to start with desoldering ?!
But seems like I already found out myself that it is the ROMs in the VIC20 which like to break down

They seem to run pretty warm for ROM chips which may contribute to the higher failure rate.

6502dude · Post by **6502dude** » Sun Nov 16, 2008 8:58 am

Overdoc wrote:But seems like I already found out myself that it is the ROMs in the VIC20 which like to break down

Good you have restored Vic-20 back to life again.

I have found that the 6560 has a very high failure rate, compared to other chips.

I don't think I have come across one yet with failed ROM.