exxos's Atari, Amiga & retro forum

Hi All,

I'm totally new to the Atari ST scene and could use a bit of help getting things sorted.

I recently picked up a 520STFM and tried doing the SMT DRAM upgrade (using the 512K J-leaded chips). When I powered it on, I got the screen in the first pic:

I then removed the chips and tried again, and this is what I got:

I’ve checked the board over — no visible defects, and I’ve cleaned and reseated all the socketed ICs. Gave the board a good clean with IPA too, just to be sure.

This is the area after desoldering:

Chris suggested I post here and ask for help – so here I am!

Any tips or suggestions would be massively appreciated.

Cheers,
DeanMachine1969

Welcome to the forum!

:welcomewave:

I'm sure you will get some good pointers from some of the other forum members.

JezC wrote: 25 Apr 2025 13:13 Welcome to the forum!

:welcomewave:

I'm sure you will get some good pointers from some of the other forum members.

Cheers JezC!

I really hope so, I've been having so much fun tinkering, I was actually planning to create my own floppy cable power/data extender before this happened. Back to The Beeb in the meantime.

Fingers crossed.

DeanMachine1969 wrote: 25 Apr 2025 13:34 Cheers JezC!

I really hope so, I've been having so much fun tinkering, I was actually planning to create my own floppy cable power/data extender before this happened. Back to The Beeb in the meantime.

Fingers crossed.

Don't feel afraid to post about your Beeb antics on this forum either - there are a few of us with one or more of the Acorn/BBC Micro range on here, so we might still spread the word and encourage a few more to add them to their collections!

:thumbup:

@DeanMachine1969 post a photo of your soldering so we can see if we can spot anything.

Another solution for that type of board is the 4mb MMU upgrade that exxos offers. You'd remove the old ram and use that instead.

You would need to socket your shifter chip if it isn't already done.

BTW, I don't think you've broken it, just not soldered it correctly maybe?

From distant memory, the vertical bars is either memory fitting or shifter fitting issues.

Try re-seating the shifter if it is in a socket.

PhilC wrote: 25 Apr 2025 14:53 @DeanMachine1969 post a photo of your soldering so we can see if we can spot anything.

Another solution for that type of board is the 4mb MMU upgrade that exxos offers. You'd remove the old ram and use that instead.

You would need to socket your shifter chip if it isn't already done.

BTW, I don't think you've broken it, just not soldered it correctly maybe?

Hi PhilC,

Thanks for responding, much appreciated. I have actually desoldered the RAM (see third pic.) I am now stuck with the 20 bombs.

Cheers!

@DeanMachine1969, ok sorry, I thought you may have resoldered them.

Look at the vias under the lower left corner of U10, they might need resoldering as there looks to be dry joints there.

In fact, looking at some of the others too, they may need resoldering. Can't hurt at least.

PhilC wrote: 25 Apr 2025 15:37 @DeanMachine1969, ok sorry, I thought you may have resoldered them.

Look at the vias under the lower left corner of U10, they might need resoldering as there looks to be dry joints there.

In fact, looking at some of the others too, they may need resoldering. Can't hurt at least.

Excellent! First task when I get in from work, I will keep you updated.

Cheers!

Can I ask how you did the soldering/desoldering? Was it with an iron or hot air?

These boards can be very fussy about hot air and popcorn, in other words the air trapped in the PCB layers expands and the board swells, which can lead to damaged vias.

If you used a soldering iron it could be something else, like a cracked via from manual handling of the board.

To start with though you need to go all through the installed RAM with a fine toothcomb to look for stray solder/solder balls/solder whiskers that could be causing shorts. I'd also check around the area to be safe for the same.

Then I'd probably check vias where you've been working and in the RAM area for continuity from the top of the board to the bottom.

After that I'd go for removing the Glue and MMU from their sockets and cleaning/tweaking the sockets (PLCC Socket contact tweaking), cleaning the IC pins and reinserting.

Also give the bottom of the board a good look over for things that shouldn't be there. I once had a piece of wire stuck to the bottom of a board that was pierced by component legs and caused a short. Not obvious but worth a check.