Problems with my Atari 1040STf

[Globox]

Hi there!
A while ago, I tried fitting a 4mb upgrade to my Atari 1040STf
I soldered some bad connections on the shifter adapter from the upgrade, and my machine didn't output a valid monitor signal anymore.
The floppy led was also not lighting up.
I put the machine back to stock, but still nothing...
I tried doing the pin fix for the mmu socket (https://www.exxosforum.co.uk/forum/viewt ... hilit=plcc)
That didn't seem to work also, so I thought the shifter went bad due to my bad soldering.
Just now, I thought I might try that MMU socket pin fix again for some reason, and I'm glad I did because my machine is doing something again!
I turned on the machine, and I saw the TOS desktop, and I could use the mouse and everything, so I thought I fixed it.
But then, after about 20 seconds, the graphics started to get glitchy, and 10 bombs appeared.
I booted up the machine a few times now, and the Atari did what I just said most of the time, but another time, it booted into TOS, and it took about 2 full minutes until the graphics got glitchy and bombs appeared. (not sure it was 10 bombs every time)
After that, the screen went white, with 3 bombs.
Sometimes it just instantly boots to a white screen with bombs (also 10 I think), and another time it just booted to a white screen (when this happened, the floppy LED lit up again).
One of the times, the monitor didn't get a signal, and I also heard a high frequency noise coming from somewhere (couldn't hear whether it was coming from the motherboard or the monitor (but I think it came from the board, and it didn't sound like it should be doing that)
I did use a real Atari monochrome monitor today, and a new exxos PSU.
Last time (before it started working again) I used a vga adapter and an LCD screen (in monochrome mode) and a stock PSU.
The VGA adapter and LCD screen still work on my other Atari, same with the old PSU, so they're not broken or anything.
Don't think those things would have anything to do with the problem, since the original Atari monitor also didn't receive a signal before I fixed the MMU socket pins today, but I can try using the LCD again tomorrow if anyone needs to know if that setup also works again now, but I'd guess it would.
I'm glad I got my Atari a bit closer to fully working again today, but I still don't know what problems there still are...
I tried to explain everything as clear as possible, so I hope someone will know what's up!

(PS. If I need to take pictures or video of what's happening, just ask and I'll do it tomorrow!)

[Globox]

Oh right, forgot to say that, apart from the PSU, my machine is still back to stock at the moment!

[DoG]

Pics say a thousand words as they say. What motherboard and revision is it?

Bad solder joint somewhare perhaps or bad connection in a socket? Or failing RAM?

[exxos]

That all sounds like bad PSU.

[Globox]

That all sounds like bad PSU.

Hmm, it's a new PSU from your store?
I'll try fitting the old PSU and see what it does!

[exxos]

I'll try fitting the old PSU and see what it does!

OK doubt PSU then. Maybe bad PSU connector ? did you use a new one ?

[Globox]

OK doubt PSU then. Maybe bad PSU connector ? did you use a new one ?

Yess I used a new connector cable.
Just tried the old stock PSU and the same thing happens...
The Atari was in a working state before, so if its the PSU, I must have done something wrong with the new one, and the old one also went bad somehow over the last few weeks, so that seems unlikely...

[Globox]

Oh and if anyone needs to know, it's a rev. C board.
I posted pictures my first post
(https://www.exxosforum.co.uk/forum/viewt ... =15&t=3371)

[exxos]

I think such faults will be very problematic to diagnose. You would need to send your board to someone like @Steve who has knowledge and experience to diagnose. But normally these old boards are not worth spending the time to repair anymore once they get to strange faults like you have. A lot of boards simply need the entire motherboard soldering, but I doubt anyone will do that.

[Globox]

I think such faults will be very problematic to diagnose. You would need to send your board to someone like @Steve who has knowledge and experience to diagnose. But normally these old boards are not worth spending the time to repair anymore once they get to strange faults like you have. A lot of boards simply need the entire motherboard soldering, but I doubt anyone will do that.

I've finally got a scope, and also got a multimeter, so I can measure things out.
But yeah If there could be a problem literally anywhere on the board, that could take a long time...

Thing is that sending out the board for someone to repair (or at least diagnose the problem) is probably more expensive than just buying a new Atari, so I'd rather just try out some stuff myself and see if that fixes it, since that doesn't cost anything...
Worst thing that could happen is that I can screw up my board even more, but that doesn't matter because unless I fix it, I'll already have to get a new Atari anyways.
I'll try tinkering with the MMU socket again, because my previous problem of my system not outputting a valid signal was fixed by doing that...
If that doesn't do anything, I can even try my other Atari's MMU and see what that does.