Strange STacy wire?

[Darklord]

I've got this single red wire on my STacy's motherboard that I've never quite figured out what it
does or where it goes to. It's never been connected to anything since I've owned it. I've got a
few other STacy motherboards, as well as a non-functioning STacy and they all have the same
wire. So...does anyone know what function it serves? Is it for an option only on certain models
or something for testing? Thanks. I'm just curious about it.

20240527_142310.jpg (363.95 KiB) Viewed 1389 times

[stephen_usher]

Early WiFi antenna?

[sporniket]

From your picture, we see that the wire is soldered to a wide track that also leads to a capacitor. Check continuity between the wire and VCC.

Also, on the stacy page from atarimuseum.de site : http://www.atarimuseum.de/stacy.htm ; there are a lot of pictures

We can see the same wire (green), this time soldered to the CPU. If I count correctly, it is soldered to the VCC pin #49 of the CPU (click on the picture of the closeup of the CPU).

So my best guess is that it is a factory bodge because at one point their was a problem with the VCC traces to the CPU ?

[Darklord]

Early WiFi antenna?

Hehehe, I suppose anything is possible.

[Darklord]

From your picture, we see that the wire is soldered to a wide track that also leads to a capacitor. Check continuity between the wire and VCC.

Also, on the stacy page from atarimuseum.de site : http://www.atarimuseum.de/stacy.htm ; there are a lot of pictures

We can see the same wire (green), this time soldered to the CPU. If I count correctly, it is soldered to the VCC pin #49 of the CPU (click on the picture of the closeup of the CPU).

So my best guess is that it is a factory bodge because at one point their was a problem with the VCC traces to the CPU ?

Good catch. On mine, the red wire was taped to the chip above the 68000. I don't remember it ever being connected but now
I'm wondering if when the CPU was removed and socketed, that when it was done, they disconnected the red wire and never hooked
it back up?

I grabbed the picture you're talking about:

STacy Bodge Wire.JPG (171.28 KiB) Viewed 1363 times

[Darklord]

Hmm, maybe take a look at the STacy schematics and see what it says about that track/capacitor
on the motherboard...

[Darklord]

Okay, I had posted this over at Atari-Forum as well and I got a response from "Arne". Here it is:

"Arne wrote: ↑Wed May 29, 2024 9:33 pm
"That is a factory patch! I sent the description to Michael Ruge and it has been published in Chips'n Chips for decades now
I found an original Atari hardware bug on a Stacy with a 103999-001 Rev.2 board. Atari then implemented a 'workaround' with a wire. On the mainboard, with the above-mentioned board revision, pin 49 of the CPU is GND. The 68000 requires Vcc here. So Atari cut off the pin above the board and put a wire on the Vcc side of the LCL combination L54. In my case, it's a green cable. Since pin 49 is neither visible on the top nor bottom of the circuit board, but is on low potential, it must be a multilayer. So you can't just scratch the PCB. The above patch should be taken into account when making your own modifications. On my Stacy, I have the c't IDE controller under the CPU, and that only worked after I had insulated pin 49 of the controller from below."

I don't think I've read through "Chips 'n Chips" in a very long time (if at all) and don't recall the STacy there.

That is my STacy's motherboard, assuming that Rev.2 and Rev.B are the same?

So what are the consequences or symptoms if you don't have this wire connected? I've been running mine for decades without it.

If the 680000 is socketed, say for an accelerator like an AdSpeed, T25, or Pak 68/3, should that wire be connected to pin 49 of the
CPU socket?

I did attempt to read something in the schematics but I'm not good at that. Here is what I found:

Capture.JPG (168.45 KiB) Viewed 1299 times

Thanks all.

[sporniket]

The picture is just a reproduction of the silkscreen, that only shows the place of each component.

EDIT : got the schematics from Atari Document Archives ( https://docs.dev-docs.org/htm/search.php?find=_6 , the item "Atari STacy Schematics (smaller file)"). I underlined the connection between +5V and pin #49 (i guess, because manual writing).

Capture d’écran du 2024-05-31 18-28-07.jpg (198.31 KiB) Viewed 1246 times

EDIT 2 : what you could do is to remove the CPU, then on the socket, check continuity between pin 49 and and 14. If there is continuity, as your wire is dangling in the air, I would guess that your motherboard is a revision that does not suffer from this problem and is not needed.

[Darklord]

Thanks for that. I'm glad someone can read the schematics - I certainly can't.

I'm still wondering what would be the results or symptoms of this, both connected
and unconnected, vs whether the motherboard needed it or not?

Thanks again.

[sporniket]

well, at the very least, it seems that it did not destruct the CPU (by creating a short circuit between +5V and ground through the 2 +5V pins of the 68000), but by the short excerpt given by Arne, I can imagine that it disturb the power rail, not enough so that a stock unit "kind of works" albeit with some strange errors from time to time, and when adding more demand with modification, it just does not work.

Of course, that is just a wild guess, as I am no engineer in this domain.