8K RAM Expander, One Bad Chip

[chysn]

My VIC-1110, which has been circling the earth with me for 37 years, is sick.

Its behaviors are strange, but I've isolated the problem to the $2800-$2FFF memory range (with my 8K RAM starting at $2000).

I'm assuming that this is U2 on the board. Can anybody confirm this? I'd like to get this up and running again, and it would be a simple enough fix if I knew which chip I had to replace. I'm willing to desolder one, but not four.

[Mike]

I'm assuming that this is U2 on the board. Can anybody confirm this?

Taking a sharp look at the schematic filed at http://www.cbmhardware.de/vc20/vic1110_11.gif: yes - U2 is connected to 1Y1 of U9, which signals the active-low CS when CA11=1A=1 and CA12=1B=0 - which corresponds to the $0800..$0FFF range of the respective BLK.

Good luck!

[chysn]

Thanks once again, Mike!

[Mike]

Did the repair work out in the meantime?

If you happen to have a surplus of 2Kx8 SRAMs, you might also consider populating the empty positions, the corresponding stabilizing capacitors and the second DIP switch (though take care to open the jumper pad of BLK2 beforehand). This way you upgrade your 8K RAM expander to a version of the VIC-1111 which can be mapped to any combination of two BLK areas.

[eslapion]

I am a proponent of the 32k upgrade myself. As discussed elsewhere, you can fill in 3 of the 4 empty positions with 8Kx8 SRAMs to get this result.

[chysn]

Did the repair work out in the meantime?

I just got the chip in the mail. Hopefully I'll have time to put it in this week.

If you happen to have a surplus of 2Kx8 SRAMs, you might also consider populating the empty positions, the corresponding stabilizing capacitors and the second DIP switch (though take care to open the jumper pad of BLK2 beforehand). This way you upgrade your 8K RAM expander to a version of the VIC-1111 which can be mapped to any combination of two BLK areas.

I am a proponent of the 32k upgrade myself. As discussed elsewhere, you can fill in 3 of the 4 empty positions with 8Kx8 SRAMs to get this result.

I do already have a 32K expander, so I don't need to upgrade this one. I hope to fix it up while keeping it as original as possible.

[Mike]

I do already have a 32K expander, so I don't need to upgrade this one. I hope to fix it up while keeping it as original as possible.

Well that's fair enough.

TBH, same applies to the VIC-1111 I happened to find (and buy) on a retro fair two years ago.

[chysn]

Wow, January? Where does the time go?

I completed this repair today. Instead of carefully removing the bad chip (as when I removed a VICmon ROM), I sliced through the pins of the bad chip without regard for it. Unfortunately, I got a little too careless and wound up destroying two solder pads; so I had to go back and make the appropriate connections with some 30 gauge wire. Lesson learned (I need better snippers, beware torsion, etc.) and no harm done.

While the iron is hot, I'm going to install at least one socket in the other half of this thing, so I have more ways to test my EPROMs. I'm thinking that my final unexpanded VIC dev environment is going to wind up on a VIC-1110.

Thanks!