520ST fully working and upgraded

[rubber_jonnie]

A while ago, I got a 520ST from exxos, knowing full well it wasn't quite right, and prepared to have a go at bringing it back to life. It seemed the right thing to do, because cosmetically it was in very good order.

So first off I resolved the problem of no PSU by building one (https://www.exxosforum.co.uk/forum/viewt ... &hilit=PSU), then resolved the problems with RAM. There was track damage due to a piggyback expansion, and in the end I felt it was simpler to remove all the RAM and fit a SIMM adapter to the MMU and Shifter, so having done that the machine was finally booting to desktop.

That left two problems:

1. The floppy drive didn't work,and any attempt to access a disk crashed the machine.
2. The TOS was version 1.00.

I'm happy to say the day is finally here where there are no problems left :)

I thought I'd tackle the FDD problem first, since I knew the machine was working upto getting a desktop.

That's where the diag cart came in, and on running a floppy test, this was the result:

Diags.jpg

Having already tried swapping the DMA, FDC and YM chips for known good items, they were ruled out, leaving the GLUE and MMU. Since the MMU had a memory adaptor plugged in, it had to be GLUE first, and lo and behold, with a replacement GLUE installed, the FDD sprang back into life :) I'll test the GLUE on another machine, but it certainly looks like it's had it's day.

Success.jpg

The TOS upgrade was simple. I sourced some PROMS from evilbay, and split a TOS 1.04 image using ROMSPLIT on Hatari to get the 6 ROM images I needed and burned them.

Once swapped out,everything worked like a charm.

Working.jpg

And I'm very happy to have this lovely machine back in the land of the living. I'll get it back in the case, hopefully tomorrow, but I think I'd better have a dig for some 1MB SIMMs and see how it likes 4MB first :)

I guess it might also be worthwhile seeing how it likes SMonson's DVI adapter whilst the lids off too.

[PaulJ]

Nice work @rubber_jonnie .. :cheer:

[exxos]

:bravo:

[PhilC]

Well done @rubber_jonnie . Always fancied one myself too. Will keep a look out I guess.

[rubber_jonnie]

@PhilC They are lovely machines 😁

[PhilC]

@PhilC They are lovely machines 😁

A bit more of a challenge to upgrade but that's part of the fun.

[rubber_jonnie]

And here we are back together and playing nicely :)

Reassembled.jpg