Commodore 128 - Startup advice

[AndyG]

Morning

I am messing about with a 128 and would like to ask for advice..... As background, this computer has had some of it Memory chips replaced and it boots fine in 128, 40 column config . I had to replace another memory chip myself to enable it to boot into C64 mode without an Out of Memory Error.

It now appears to works fine in both modes as far as I can tell. I am used a SD2IEC device to load programs etc.

It will run GEOS fine, though it will not run Invaders (128 mode, 40 column) - just get blank green screen.

Now to the issue.... if I boot (128 mode) from cold I sometimes get a garbage screen (with green border). If I hit the reset button (or restart it again) it will boot to the proper startup screen and work OK. If I have a joystick plugged into Port 1 (after using GEOS and the Joystick to move the mouse pointer) then I may have to do this a couple of times to get it going then it seems to works fine after that.

This morning after being powered down overnight, it booted fine - this garbage screen issue appears a little random!

It seems to boot directly into C64 mode with no problems if I hold the C= down whilst powering on.

To address the startup issue

• Do you think I may still have a memory chip issue on the lower bank (assuming C64 mode uses the other bank and works fine) - if so I will just remove the old memory chips and replace with "newer" types ?
• Should I recap the board as the issues seem to be from cold boot ?
• Should I do both ?

Cheers
Andy

 

[KC9UDX]

I have a PET that does this. The longer it sits, the longer it takes to get it working.

It starts out by getting garbage screens (PET typical), then starts getting PET atypical garbage, then screens full of randomly placed dollar signs. Eventually it gets an almost normal looking startup screen with "... GOMMODOVE FAWIG 4.0 ..." and some totally absurd amount of free RAM. Then a few more reboots and it's normal and very reliable.

It may be RAM, or something else in the data path, I don't know. It hasn't bothered me enough to diagnose it yet. Yours may be RAM or a plethora of other things, given that you have dynamic RAM and a PLA.

One thing I don't really suspect is capacitors.

 

[AndyG]

Thanks KC9UDX

Not responded until now as have been trying to figure out what was wrong. It seemed the previous owner lifted/broke a few tracks whilst replacing some of the RAM, causing these random errors. As the issues were numerous, I ended up carefully desoldering the RAM, locating the bad tracks, repairing them and installing sockets (embarrassingly even after the MB had been thrown in the trash as I was spending too much time on it and lost patience with it as I missed one last track that was broken. Just wouldn't be beaten).

Works Fine Now!!

 

[KC9UDX]

Nice work!

It always pays to be persistent.