IBM PCjr Character Issue

[MaCJaX]

Greetings All !!

I finally got my IBM PCjr up and running but it does have an issue. Looks like a bad RAM IC or Character ROM IC maybe ? Not really sure and was looking for a little advice. Please see attached pic. That's the BASIC screen. Thank you !!!!!

 

[IlikeTech]

I don’t think the PCJr has a separate character rom. Does the splash screen look normal? If not I would guess this is a ram issue, as it uses system ram for video.

 

[Gary C]

Almost looks like its trying to write double height characters on a single line.

 

[MaCJaX]

Yes, the splash screen looks normal except for when it does the mem count. The mem count looks like it does on the BASIC screen. Thanks !

 

[mbbrutman]

The PCjr does very much have a ROM for the character generator. It's basically the same as a CGA card, but with some more graphics modes, circuitry for sharing the memory with the main system, and an ASIC is used to implement it.

It also looks like the addressing to the character ROM has failed. Try to boot up a game (something that is pure graphics) to see if the fault continues there. If the game looks normal then it's the character ROM or the addressing logic to it that needs attention. (I think that in the graphics modes the text does not come from that ROM and comes from a bitmap in the BIOS ROM instead, so text displayed in a graphics mode is a good test too.)