VIC-20 with junk text at the bottom

[gamer-stu]

I lucked into acquiring two VICs with PET style keyboards. One works perfectly, and the other is experiencing a fault.

The faulty one turns on to the standard screen, displaying the RAM, but also a consistent line of garbled text at the bottom. It then freezes. I ran it with a game cart (Mole Attack), and it works fine, but with some graphics glitching at the top right of the screen.

Things I’ve tried:

- reseated all socketed ICs. No change.
- swapped the Basic and Kernal ROMs with known good ones. No change.
- swapped the VIC chip with a known good one. No change.
- nested a known good RAM chip on top of each RAM IC. No change.

Next step will be the logic probe.

I should probably get a Penultimate+ for Dead/Test +. I’ve got the original Penultimate, but this might be my excuse to upgrade.

Any clues of where to start?

[doug_in_nc]

There is a possibility that your RAM is faulty but piggybacking wasn't successful. Have you left the machine running for a while and checked if the RAM gets noticeably hot? Did you run other games as well, and if so did they glitch in the same place on the screen? Try graphics based games and also something text-based like a Scott Adams adventure. I think there are some on the Penultimate cartridge, right?

[gamer-stu]

Thank you!

Unfortunately I do not get a basic prompt, so I can’t run anything that requires a Sys input. Penultimate doesn’t get to the selection screen anyway.

I will leave it on and try as you suggest.

Here is the glitchy screen from Mole Attack:

[gamer-stu]

No noticeable excess heat from RAM or any other chips after being on for 30 minutes. There is one chip that is about 3 degrees F warmer than the other (measured by thermometer). But I don’t think that is a large enough difference to indicate a failure.