exxos's Atari, Amiga & retro forum

Icky wrote: 04 Nov 2021 23:23 Great walk through @rubber_jonnie.

@Bikerbob following this through should uncover the underlying problem.

Thank you sir.

Yes, some of it, I have done. Today I will start going through this.. fingers are crossed. I will post results.

James

rubber_jonnie wrote: 04 Nov 2021 23:13 @Bikerbob
Ok, so let's just wind things back a moment. I know this may all have gone before, but a re-cap is always useful.

Do you mean re-capping the board as well? I will today do my tests with the Delta psu - new and I can use it off the board.

rubber_jonnie wrote: 04 Nov 2021 23:13 I know you have checked for bad chips with freezer spray, but also if you can touch them to see if any are running hot once it fails. This is all major chips plus the RAM.
Have you used a magnifying glass or microscope to look for bad solder joints on the main chips?

YES I have - nothing I can feel... also right after the failure - this was days ago.

rubber_jonnie wrote: 04 Nov 2021 23:13
If you haven't already done so, remove the GLUE and MMU and follow this guide: https://www.exxosforum.co.uk/forum/viewt ... hilit=plcc to reset the socket pins. Blitter too if fitted.

All chips were removed - all sockets checked, all pins cleaned. The Blitter is a new one from Best Electronics (one for H5 one for this board)

The rest of what you suggested I have done is spurts and starts.. Tracing all the addressing and data lines, as far as I have been able to figure out. I will have to do better on this, since this seems to be a real possibility of the issue.

Anyway.. busy next few days.. I will let you know.

James

@Bikerbob

By re-cap I don't mean replacing the capacitors, I just mean go over what we already know and write it down for reference.

rubber_jonnie wrote: 05 Nov 2021 15:49 @Bikerbob

By re-cap I don't mean replacing the capacitors, I just mean go over what we already know and write it down for reference.

LOL>>>> too funny.. ok

So yesterday the damm thing lasts almost all day running except 2 fails on ram checks.

Today .. fails in 2 mins again.. :(

Power on the lines is not consistant. yesterday I was getting over 5v on 2 different psus. Today I am down to 4.8v thoughout the board..

James

Bikerbob wrote: 06 Nov 2021 21:53

rubber_jonnie wrote: 05 Nov 2021 15:49 @Bikerbob

By re-cap I don't mean replacing the capacitors, I just mean go over what we already know and write it down for reference.

LOL>>>> too funny.. ok

So yesterday the damm thing lasts almost all day running except 2 fails on ram checks.

Today .. fails in 2 mins again.. :(

Power on the lines is not consistant. yesterday I was getting over 5v on 2 different psus. Today I am down to 4.8v thoughout the board..

James

FYI there are 4 capacitors in the 'power in' circuit on the schematic, C4,C5,C8 & C9.

C5 & C9 look like tantalums, so are probably ok, but C4(5v rail) and C8(12v rail) are electrolytics.

Now 12v isn't required to boot the machine, just for some specific circuits, so C4 on the 5v rail might be problematic and causing instability of the 5v rail.

rubber_jonnie wrote: 07 Nov 2021 10:49 FYI there are 4 capacitors in the 'power in' circuit on the schematic, C4,C5,C8 & C9.

C5 & C9 look like tantalums, so are probably ok, but C4(5v rail) and C8(12v rail) are electrolytics.

Now 12v isn't required to boot the machine, just for some specific circuits, so C4 on the 5v rail might be problematic and causing instability of the 5v rail.

Ok something to look into! :)

Ok, pullups have been done. The WD1772 resistor array done. I have replaced the onboard 4700uf cap.

No idea if any of that actually helped, but I can now run the board for days at a time - WITH NO FLOPPY DRIVE attached. and it seems to run the DIAG cart all day.

EDITED - I have read a lot on the DMA on Exxos site and else where. I have had a lot of the Floppy issues with this machine that Exxos described. bad data, floppy corrupt. and now finally these issues.

Do you think this DMA could be bad? not the little issues that happen.. but actually going bad? crashing the machine.. more specifically when I am going to use it.. AKA .. the machine seems to work if I dont have floppies connected, or my COSMOS.. dma port.

I might try swapping a DMA from another machine.

james

What DMA chip is actually in there ?

one of the "bad" ones..

But it did show some of the "faults" you described.. but more I am thinking that parts of the chip are actually bad.. if used.. maybe the reason why the machine is working when I have no DMA devices at all.. is because its a fault of the chip???? possible?