exxos's Atari, Amiga & retro forum

Hi retro fans..
I go by the name Vipersan.
I'm 68 years young and repair/maintain a lot of computers though I confess most of these are commodore or PC.
In short I have a bit of a museum thing going on.
I have never worked on Atari but recently was gifted an Atari 520 STe in non working condition.
Black screen.
I deduced the Xhalt line was being activated...this turned out to be 2x open traces between CPU and roms.
traces fixed I was rewarded with the GEM green screen.
but that was only the first hurdle.
Connecting up a floppy drive resulted in ..well...nothing.
I suspected it was damaged at first..but now I'm suspecting a problem on the mainboard ...having tried a modified Sony and getting the same result.
So I purchased a diagnostic cart pcb ...but although it boots can take up to minute to display all the menu options.
Surely this can't be right ?
A lot of the tests passed ..but noteably the floppy test failed as did the DMA test which I am assuming can be floppy related ?
At this point I am asking for help ..which is why I joined Exxos foum today
regards to all
VS

:welcomewave:

If the DMA and CPU are in sockets, first point of call is to reseat them. Also a image if your board would help as there are several revisions.

Board revision is CA4003290 1989

CPU has already been removed ,...socket had deoxit applied then reseated

:welcomewave:

Welcome to the forum!

Welcome - you're gonna love it! :)

@Vipersan

So my first question to you would be 'are the drives set to ID0?'

Although you mention a modified Sony drive, you don't say what the mod is and all ST drives should be set to ID0.

If the ID is set to 0 and the drive is correctly connected I'd run the floppy tests from the diag cart and see what the results show.

Yes the original and the modified floppies are set to drive ID zero.
Both of which are seen ...they both pass the motor speed test.
When testing the heads move....but neither drives read write..format etc.
Having just watched a youtube video from retro computing reboot ..(
I'm now fairly convinced that the DMA chip is likely suspect.
Apparently failed DMA chips are common.
The blank floppy experience is just the same as mine...and I know there is data on the disk.
Next question is where would I get a suitable 40 pin replacement...?
rgds
VS ...and thanks for the warm welcome :D

So it would appear I do indeed have the 'dodgy' DMA chip in this Atari (CO25913-38)
Found someone on ebay selling similar for £3 each ..they could be fake of course ...but took a chance and placed an order for 3 pieces.
Tomorrow I will attempt 40 pin chip removal and fit a socket.
Just hope I dont damage the pcb in the process.
..and apologies to Exxos for splitting the thread.
It wont happen again.
rgds
VS