Atari TT - Bus errors, advice needed! - SOLVED

[Steve]

Hey guys,

I'm getting heaps of bus errors on my TT. They either show in TOS by giving me 2 bombs or 3 bombs sometimes, this can happen as soon as the desktop appears or if I'm loading a program from floppy. When loading Mint from HDD I get the following bus errors:

IMG_20180730_122354.jpg

IMG_20180717_130542.jpg

If I enable memory protection, the error message changes a bit:

IMG_20180718_173531.jpg

IMG_20180730_122246.jpg

Also - the floppy drive and SCSI interface seem to be acting strange. When loading data from floppy it can cause a 2 or 3 bomb. Same if I try my SCSI2SD it can lock the system up or crash.

My configuration:
TT030 C302406-001 REV H:
https://www.exxosforum.co.uk/forum/viewt ... f=58&t=999
Thunder IDE interface and Storm TT ram (64mb)
Lightning VME

What I have tried so far:
* I have re-capped the PSU and the entire motherboard
* I have replaced the 7406 WD floppy controller (got the floppy controller from exxos, the 7407 from element14)
* I have removed ALL add-on cards, thunder/storm/lightning, also removed ST ram card, I still get random bombs 2/3 in TOS.
* I have run YAART memory test on TT/ST ram without any problems
* I have re-flowed the soldering on many important connectors
* I implemented a VME fix recommended by Atarian computing

No changes, same issues persist.

Stuff that does work:
* I can load games, for example Frontier - and just leave it running for hours, no issues
* Thunder IDE interface seems perfectly stable, using latest HD Driver 1012
* TT ram card storm works fine
* VME graphics card works fine - can run in high res 1280x1024 no issues
* Mint can load to the desktop, it can run applications like Papyrus etc. But will sometimes throw up the bus error.

I really hope someone can help me solve this problem!

kind regards,

Steve

[exxos]

If it all works before loading mint, then seems like a software fault ? You say you can run frontier, so doesn't sound like a machine problem.

[Steve]

No it doesn't, like I said in TOS (not in Mint) it will give me 2 or 3 bombs when loading from programs from floppy. Also the scsi can lock up. Sometimes it will magically load from floppy too, but often not. Sometimes it will try and load HDdriver from floppy and bomb on the detecting drives list. I think 3 bombs means bus error, and I was showing the Mint screen to further demonstrate bus error.

[exxos]

Bad floppy cable ? bad rom sockets or bad roms ?

[mikro]

Maybe also wrong/damaged SCSI termination? TT has always been picky about this one.

[Steve]

I tried a different floppy cable. Perhaps I can put my original TOS roms in, at the moment I am running the custom ROMS that came with thunder/storm. I will try that.

[frank.lukas]

When you use not a external SCSI Device the internal SCSI Device should be terminated and the Mainboard should be terminated too.

[Steve]

When you use not a external SCSI Device the internal SCSI Device should be terminated and the Mainboard should be terminated too.

Yes the internal scsi is terminated. Plus these symptoms show without the scsi device connected.

[Atarian Computing]

Dang. At this point I'd start looking for corroded/damaged traces with a magnifying glass front and back. The behaviour you describe is typical in a TT when there is damaged circuit.

[Steve]

Quick update:

* noticed that if I remove the ST ram card the machine will boot from floppy and read the floppy fine
- But when loading mint it still gives a memory address / bus error in the system log
* Running yaart crashed with the ST ram card installed, but not with it removed

I know you could assume that it's related to the ST ram card but I don't think so as Mint will still show a bus error upon loading, but with it removed does solve the floppy issues. I am feeling that it's something to do with memory address allocation, where adding the extra memory space causes issues or makes the issues worse somehow, but I still feel the issues are underlying even without the card installed.

Could some of the TT experts let me know what they think of this? Is there a certain chip in charge of memory allocation. Could adding the ST ram card cause something to do with how the floppy uses memory space/locations?