PhilC's H4 Mongrel edition build x 3

[PaulJ]

@PhilC , I've noticed that any simm that has ram on both sides doesn't work while all simm's with ram on one side all work independent of size. So I guess you can't read the screen at all. Better get the serial working.

[PhilC]

@PaulJ just swapped out my 8mb double sided for a 4mb single and it's more consistent but still garbage on the screen.

Is best go unsolder some serial ports then.

[PaulJ]

Sounds like a good plan @PhilC , if you think diagram is running then most of your data and address lines should be ok. Ya know it would be cool to have a 68k board with a serial port and rom limited to a small decoded footprint in an unused memory area so you could checkout the board from it. In essence to have the serial port running on an Atari a lot has to be functional.

[PhilC]

@PaulJ yes I've learned from the Alpha to get as far as the serial working on the first power up is pretty cool.

Verified that it is a ram fault thanks to Diagrom, probably more dodgy soldering,

No more time tonight to continue with the fault finding, so I'll just leave this screenshot here

20200112_200235.jpg (438.71 KiB) Viewed 3434 times

[PaulJ]

@PhilC , that's pretty screwed up. Its not like you have a bad bit or so.. six nibbles that don't change and the two that change are quite random... did you get the U57, U58, U60, and U61 in right? Good that your rom is being accessed properly.

[PhilC]

Yes I did get them in right @PaulJ , although picked up one old one, so its possibly that that's failing. All part of the fun and a job for my scope next week

[PaulJ]

Ya, looks like something pretty futzed up. Sure you'll find it.

[PaulJ]

@PhilC , I've been thinking about your memory issue. As you say diagram is executing code but you display shows a totally chaos on the dram best diagrom is able execute code and access the serial port. Its got to be something with the dram buffers or the MMU. If it was a short or bad solder joint on the dram most likely only a byte or two be be bad. Just a thought.

[PhilC]

@PhilC , I've been thinking about your memory issue. As you say diagram is executing code but you display shows a totally chaos on the dram best diagrom is able execute code and access the serial port. Its got to be something with the dram buffers or the MMU. If it was a short or bad solder joint on the dram most likely only a byte or two be be bad. Just a thought.

Thats exactly what I think as well Paul, since it boots Diagrom but goes nuts with memory faults. Hopefully get time to check my soldering later.

[PaulJ]

@PhilC , my money is on something with the MMU.. You have so many bad bits I doubt that its soldering issues on the simm or address and data lines but maybe some shorts or opens on the mmu inhibiting it from normal functionality. Get her going Phil .