Mega ST small PCB function with connection to floppy power connectors

[mathias_matschke]

Hi Forum,

Need your inside please. in my newly acquired mega 1 there is a very small daughter board installed, which I did not see before. It connects to the second floppy power connector. And the black cable goes to the floppy shield. Does anybody know what the function may be. The computer behaves 100% normal.

Thanks.

Mathias

IMG_1009.jpeg (787.88 KiB) Viewed 655 times

[czietz]

Would be nice to see where exactly each of the six wires is going to. It wouldn't by any chance connect to the fan, would it? Photos please.

EDIT: Seeing that this is a German MegaST (based on the TOS ROMs), it might also be an idea to ask at https://forum.atari-home.de/, if someone there remembers this kind of board from "the old days".

[czietz]

Apparently the poster's question wasn't so important to him...

[Badwolf]

@czietz,

Since he's not come back, let's speculate wildly.

It sits over the RAM address and control line buffers, but I can't see that's for any real purpose. If it were tapping the chips it would likely take its power from there too.

It has two pots. My initial thought was voltage divider, but why would you need two, in that case?

Some kind of heatsink at the bottom?

I thought the big black lead may have been extra grounding, but why then two? "Attaches" to the floppy shield?

You mentioned the fan -- this might make sense. Could the black wires lead to a thermocouple, there's some kind of regulator hidden under the heatsink and the pots set a high and low threshold for a variable voltage output driving the fan according to temperature?

BW

[czietz]

You mentioned the fan -- this might make sense. Could the black wires lead to a thermocouple, there's some kind of regulator hidden under the heatsink and the pots set a high and low threshold for a variable voltage output driving the fan according to temperature?

That's what I was thinking. The black wires could be a thermal sensor like this: https://i0.wp.com/circuitcellar.com/wp- ... =640&ssl=1, which might give the impression to be "attached" to the floppy shield.

I know that comparable fan control circuits, using a transistor with heatsink as regulator, exist for the MegaST. Hard to say, however, without the original poster showing where all the cables lead to.