exxos's Atari, Amiga & retro forum

Hello everyone !

I have been the happy owner of a 520 STM (C070243 Rev B + 512Kb) for several years.
It has been in its box, in my HQ almost since its acquisition.

For what ? Because when I first plugged it in, everything worked fine.
I was able to happily play Defender of the Crown for a few hours.
Then suddenly, bombs !!!! And there, the ST started to do as it wanted.

Once it stays on white screen, once white screen at startup + 4 bombs, once white screen + artifacts...
Often, it arrives at GEM, but I no longer have access to the floppy disk drive, which is nevertheless recognized.

What I have done :
- Changed the PSU + MB electrolytic capacitors ==> this improved the behavior of the floppy drive (the motor stopped turning, did anything)
- I've tested the FDD with my Greaseweazle : fully working
- Cleaning the MB + cleaning the IC legs on supports.


I don't really understand where this could come from.
I don't have a diagnostic cartridge yet. If, with your advice, I can avoid buying one, that would suit me :)


Thx in advance :)

Hanabi.

You can try the standard things like reseat the TOS, MMU and GLUE chips. You have a piggyback RAM installed according to the picture. You should check all the solder joints are in order to the RAM chips, they can be a lot of trouble. If you disconnect one of those grey wires going to the RAM chips you can see if it will boot correctly with just 512K.

Indeed, reseating the PLCC chips with some good quality contact cleaner is the first item on the list. Of course, this means getting a good PLCC chip lifter first.

+1 for PLCC socket checking.

So many times on my -FM I think I've broken something in my verilog just to realise I need to tap the MMU a few times and press reset.

Some (most pre-STE?) models shipped with metal clamps over the two main socketed PLCC chips. Mine obviously had them in the past and were removed by a previous owner. I imagine they were there for a reason!

BW

+2 for PLCC chip/socket cleaning.

Also +1 for getting a decent PLCC chip puller first, don't be tempted to try lifting out with screwdrivers.

Thank you for your answer !
Everything was done except the PLCC's : my shifter is too wide, I ordered another one.

A strange thing happens: since I took the photos, not once have I experienced crashes at startup. I conclude that even my Atari is making efforts to survive :lol:

See you soon for the rest.

Hmm. I'm not very proud of myself on this one :roll:
My problems reading floppy disks were due to a too weak FDD PSU :oops:

Everything is not settled yet : I read some floppy disks but not others (commercial games). Despite this, no game launches (although this was the case before).

In short, I will let you know what happens next as soon as I receive the chip puller.

Hi there !

The STm is getting better !

To summarize, I have:
- Re-cap PSU and MB (only electrolytics)
- Redid some soldering (a lot, in fact, notably those of the RAM mounted in piggyback, and the PSU, video, mouse/joystick and FDD ports)
- Cleaned with contact spray all chips on support
- Added a 7805 and a filter cap into the floppy drive case. What a beautiful piece of shit, this RF302RC !!! It was really an idiot trap, this messed up PSU story !

I still have to create a floppy disk with some test tools on it (e.g. yaart) to further test the machine.
The rest (and end, I hope !) after the tests :)

:girldance: