Mega STE - Attempting a repair!

[displaced]

Hi all!

I’ve just got a known-bad MSTE for a decent price as a bit of a project to work on. I’m probably the very definition of ‘all the gear and no idea’, but I’m keen to learn!

I hope you don’t mind me posting my findings here - and any help along the way greatly appreciated.

Anyway - it powers on to a white screen and nothing else. Reset appears to behave - video signal disappears whilst Reset is held, and reappears when released.

This machine had clearly been messed with. The GAL at U81 had been fitted for the FPU and the W3 jumper had been opened, but there’s no FPU present.

I’ve removed the GAL and re-jumpered W3. No difference.

The GAL at U11 had been hacked at. The first pin towards the front has a solder blob on it, whilst the 4th pin has had its leg cut off. I’ve fixed that and it beeps fine between the leg and the socket’s solder joint on the underside of the board. Not sure I trust it though.

I’ve checked the following and hope I’m drawing the right conclusions:

68000’s RESET - low when reset held, high when released and stays there (good)

HALT is high during reset but goes low a moment after (bad)

BERR blips low shortly after releasing reset before staying high (bad).

I think my next step is to pull and reseat everything I can, paying attention to the PLCC contacts, which I’ll tease outwards a little.

One quick question - the 68000 is rather toasty. Can hold a finger to it for about 6 sec before its too much to take. Does that sound about right?

Cheers,
Chris

[exxos]

One quick question - the 68000 is rather toasty. Can hold a finger to it for about 6 sec before its too much to take. Does that sound about right?

Yeah they get feking hot. I think its because its a 8mhz NMOS part being pushed to 16MHz. I swapped one out for a HC type and was a lot cooler.

[stephen_usher]

The first thing I'd do is buy a diag cart from Exxos, that will help no-end with finding out what's wrong.

[DoG]

Just a check; You know that you have to wait up to a minute to get GEM to show if no floppy is in the drive?

Did you have floppy disk drive attached when startup? Does that give any sound at boot?

TOS 2.06 show splash screen and test RAM etc.
TOS 2.05 just show white screen on boot.

Sorry, but I just had to ask since sometimes people asking how to repair an Atari, thinking it is dead, when in fact, it is working.

[displaced]

Brilliant -was eyeing up an HC on your store, but I think as Stephen says, a diag cart will probably be the next purchase!

Is there anything I can check with the scope to tell if the thing is likely to be functional enough to run the diag cart?

Have carried on stripping the machine down... the SCU’s got telltale screwdriver skidmarks across the top, but there’s no marks at all on the socket. Wondering if the chip is a replacement from a previous attempted repair.

Seriously hoping it’s not the GST... I don’t think I’m ready for that level of soldering yet!

Had a poke around looking at clocks, which all seem good. Tomorrow I’ll swap in the known good SIMMs from my Marpet-ed STFM.

Oh and there’s a hair trapped in pin 5 of U5... and it’s definitely not one of mine 😲😂

... just seen your reply, DoG - yeah, I’ve been making sure I wait for at least a minute. Used to always have a blank floppy at hand back in the day to help me get to GEM quickly!

ROMs are labelled C302020-002B and C302021-002B which is apparently 2.05. I’ve programmed a couple of 27C1000s with 2.06, but didn’t want to change too much at once whilst debugging.

Presumably 2.05 would eventually get to GEM (or at least show something... bombs perhaps) without a keyboard, floppy or hard drive? Oh, and I’ve removed the SCSI host adapter too.

[displaced]

Only gone and bloody fixed it... ish...

Thought I’d have a peek under the PSU before stopping for the night...

Thought the SCC looked like it had been fiddled with. Checked a photo online and it was rotated 90deg left in its socket.

Pulled it and put it in the right way, and for giggles fitted my home-flashed ROMS...

Atari logo appears!

Memory test completes, but stops after with 4 bombs.

Progress at least!

[PhilC]

Nicely done, 4 bombs is no floppy drive connected.

[displaced]

Apologies for spamming the replies, but just found out about the ‘missing FDD=4 bombs’ thing on 2.06.

FDD refitted and... hello there, little green desktop!

Absolutely thrilled! Now got a MSTE to sit with my STFM and Falcon. Really glad that there’s another working one in the world too.

Still plenty to do. The journey from the Netherlands put a couple of cracks in the case. At least they’re clean breaks which I should be able to fix neatly.

Someone had retrobrighted this poor machine, which went badly wrong, so it’ll need a respray too. The Return key sits too low in its slot to use, and the tab’s snapped off the keyboard’s RJ11. Plus I’ve got a Noctua fan ready to replace insanely loud one in the PSU.

But I’m sure I can make this good now - excited to get going now it’s alive!

[stephen_usher]

:yay: :thumbup:

[rubber_jonnie]

Weirdly, I thought I'd replied yesterday, but I must have not hit submit for some reason!!

Nevertheless, it sounds like you have some stuff to do, so it's worth visiting here: https://docs.dev-docs.org/htm/search.php?find=_3 as there is a ton of MegaSTE stuff here.

I've also attached a zip file with the FPU and FDD upgrade documentation so you have an idea of whats what, and what you may have installed. It also has the JED files in case you need to make new GALs.

I upgraded mine with an FPU, it isn't the best solution, but it does seem to work. Similarly, mine already had the HD FDD installed, so that was a bonus.

Worth also checking if yours has the internal HDD cradle. Mine doesn't so I'm using an external Cosmosex, but it does have internal headers for ACSI and Lotharek does some internal adapters. If you can get one there is also an internal SCSI adapter, though I think it is limited to 1GB.

Good luck.