exxos's Atari, Amiga & retro forum

Hey all, having issues with my MegaST project board. I am sure this is something self inflicted, this board has been out of a case and moved around and played with a lot.
I can start it up from dead cold. works for a min or two.. or if I run the Diagcart.. I get a pass on everything for the first min or two.. then I have these.. issues.. now.. the one with the 1m memory is an indicator I think because the machine has 4m and when first into diag.. shows 4mb..so .. maybe an issue with the mmu itself?

PSU ?

On his BBS I think he commented that he had swapped out that Mega ST's P/S with
another P/S from a known working Mega ST...

Sounds like a dry joint or broken joint to me.

As something warms up something expands the the connection is broken.

Then again it could be a memory chip on the way out.

Cold spray is the way to go to try to locate the place where it's temperature sensitive.

Ah, I keep telling people about this. Just because the power supply works in one machine does not mean it will power another reliably.

I could easily have 200 PSUs here which will power up a STFM fine, but fail every time on a STE. Its why it is important to service them. If the mandatory fixes have not been done then people are just asking for trouble right from the start.

So if I had to guess from the msgs I am thinking memory? IT is an area of the board I fussed with? I put new chips in.. and installed sockets.

SO.. can I just remove a ROW? or two Row? is there a way to try and identify it?

What do you mean by cold spray?

James

exxos wrote: 28 Oct 2021 16:00 Ah, I keep telling people about this. Just because the power supply works in one machine does not mean it will power another reliably.

I could easily have 200 PSUs here which will power up a STFM fine, but fail every time on a STE. Its why it is important to service them. If the mandatory fixes have not been done then people are just asking for trouble right from the start.

Yes I hear you Exxos, I have multi MegaSTs .. it is a psu from a megaST going into it.. I am not saying it could still NOT be.. but seems like a cold joint or something... going bad.. IF I was to check the psu.. am I just monitoring the +5 +12? I cannot scope it right now.

As for the manditory fixes.. I was just using this board to test the whole cloudy/Storm/Lightning thing.. and have a number of the fixes here ready to install when this went bad.. IF I can get it up and running again.. I will do a lot of them.

james

BTW, do you have a bench PSU you can run it off? It would help knowing that your power is solid.

rubber_jonnie wrote: 28 Oct 2021 16:25 BTW, do you have a bench PSU you can run it off? It would help knowing that your power is solid.

No the only thing I have are PSU from PCs .. 300w 400w etc psu. It was one of those - smaller 110w that I was running the machine on. As a test I put the another psu from a MegaST in .. same result.

With all the movement I have put it through, I would guess its a cold, or poor joint, or maybe something "going" bad, just hoping to get an idea where to look.

The erros I have got one the diag cart.. is there any documentation as to what they are?? where I go?

James

Bikerbob wrote: 28 Oct 2021 17:13

rubber_jonnie wrote: 28 Oct 2021 16:25 BTW, do you have a bench PSU you can run it off? It would help knowing that your power is solid.

No the only thing I have are PSU from PCs .. 300w 400w etc psu. It was one of those - smaller 110w that I was running the machine on. As a test I put the another psu from a MegaST in .. same result.

With all the movement I have put it through, I would guess its a cold, or poor joint, or maybe something "going" bad, just hoping to get an idea where to look.

The erros I have got one the diag cart.. is there any documentation as to what they are?? where I go?

James

I have, I think, three Mega ST threads on here (Sorry I can't find them ATM) and at least one goes into the RAM checks of the diag cart.

Also, you sometimes see different stuff over the serial port, so worth trying that too.