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Rescuing an ancient 520ST

Posted: Sat Oct 20, 2018 10:16 am
by troed
So here's my latest project. This 520ST was given to someone in the shape it is, without cables. When the new owner tried hooking it up to 5V to get it to boot up all he saw was sparks of electricity from the mainboard ... :)

Since it has a -38 (not -38A) Shifter, and what I'm hoping for is a short-top border GLUE, I traded a fully working 1040STFM for it today.

(I'm surprised to see it has a 1MB piggyback, but from the looks of it I'm not sure it was done by Atari)

Besides the obviously very fried serial chip, there's a nick to the mainboard capacitor that might or might not be relevant. I'll not be able to do much investigation until a week from now, just posting these pictures up here to document the start of the journey.

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Re: Rescuing an ancient 520ST

Posted: Sat Oct 20, 2018 10:25 am
by exxos
wow, the electrons were sure in a hurry to get out of that chip!

Didn't know there was a -38 Shifter ? I have 3 ST's here I never touched. Probably gonna just have to start selling some machines to clear up some space soon.

Re: Rescuing an ancient 520ST

Posted: Sat Oct 20, 2018 10:42 am
by troed
exxos wrote:
Sat Oct 20, 2018 10:25 am
wow, the electrons were sure in a hurry to get out of that chip!

Didn't know there was a -38 Shifter ? I have 3 ST's here I never touched. Probably gonna just have to start selling some machines to clear up some space soon.
The -20 is the oldest, then they made the -38, followed by the -38A. Ijor has analyzed that there should be big enough differences for demos using "Shifter techniques" (not regular sync scroll, that's GLUE, but 4-bit sync scroll and Closure-no-stabilizer etc) to maybe not work at all as intended on the -20 and -38.

So of course I wanted one :D

Also, I this is an ever earlier mainboard revision than Gunstick has on his short-top border GLUE machine so I'm hoping for that as well. It's the earliest mainboard revision I've seen (there is one other in the mainboards section on here though).

Re: Rescuing an ancient 520ST

Posted: Sat Oct 20, 2018 10:47 am
by exxos
cool :)

Will have to open up my ST's and see whats in them at some point :)

Re: Rescuing an ancient 520ST

Posted: Sat Oct 20, 2018 11:28 am
by sandord
troed wrote:
Sat Oct 20, 2018 10:16 am
I'm surprised to see it has a 1MB piggyback, but from the looks of it I'm not sure it was done by Atari.
This is exactly how it looks when done by Atari so I'm pretty sure the RAM upgrade is original.
I used to own a 520+ and here's another one that has it: viewtopic.php?f=53&t=540

Re: Rescuing an ancient 520ST

Posted: Sat Oct 20, 2018 11:40 am
by troed
sandord wrote:
Sat Oct 20, 2018 11:28 am
This is exactly how it looks when done by Atari so I'm pretty sure the RAM upgrade is original.
I used to own a 520+ and here's another one that has it: viewtopic.php?f=53&t=540
Reason I said so is that the resistors are usually not placed where these are, and whoever did the mod had to extend the final part of the connecting wire with an IC leg (it looks like). It still can be, but I'm not sure it is :) The piggyback mod I've made to my own 520ST also "looks" like one from Atari.

Re: Rescuing an ancient 520ST

Posted: Sat Oct 20, 2018 11:42 am
by sandord
troed wrote:
Sat Oct 20, 2018 11:40 am
Reason I said so is that the resistors are usually not placed where these are, and whoever did the mod had to extend the final part of the connecting wire with an IC leg (it looks like). It still can be, but I'm not sure it is :) The piggyback mod I've made to my own 520ST also "looks" like one from Atari.
Fair point. So the devil is in the details, as usual ;-)

Re: Rescuing an ancient 520ST

Posted: Tue Oct 30, 2018 2:45 pm
by troed
I didn't get this ST to boot immediately, but since my main interest were the Shifter and GLUE chips I just transplanted them to my 520STM rev.I.

Success :D Closure non-stabilizer fullscreens indeed have a visible issue (every second line, every second 16 pixels black) - and it's a short top border GLUE! Looking at revisions, both of these chips are -38, not -38A - and knowing that Gunstick's old 520ST+ also had a short top border GLUE and it also has a -38 instead of a -38A as on later revisions, I'm going to tentatively assume that that's the chip revision respin where the GLUE statemachine was changed.

(The actual change is a different 50Hz vertical start position. The screen display visible starts "higher up" than normal)

edit: For Closure, all fullscreens are made in such a way that they work by default on both GLUE revisions. However, the "vertical scrolling dude"-screen which only removes top and lower border doesn't, it does not test for a short top border GLUE and thus fails.

Re: Rescuing an ancient 520ST

Posted: Tue Oct 30, 2018 3:08 pm
by rubber_jonnie
exxos wrote:
Sat Oct 20, 2018 10:25 am
wow, the electrons were sure in a hurry to get out of that chip!
Oooh, I smell magic smoke.....