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Identify a mod on my Powerbook 100


Well-known member
I now have two powerbook 100, the first one has been recapped, etc, and is doing good.

The new one is currently undergoing the same repairs.

However, now that I have two, I noticed that my first one has not only a relatively rare ram expansion, but it has somekind of a "mod" that looks stock to me, that my other powerbook 100 does not have


Does anyone know what this is ?

Do you have such a thing in your PB100 ? Its seems to be an "afterthought" set of pull down resistors (we can clearly see a common ground) to various signals

Does that make my PB100 special ? :) Am I rich ? (just kidding)

Curious to know more

I'm trying to built the "best" PB100 possible out of my two units, and clearly this mod seems to be an aftermarket fix for god knows what (i've seen pictures of this same thing on Reddit as well - but nobody knew what it was there).
So if this fix makes the thing better, I have to replicate it or move it to my "better" unit.

For what I can see, this seems to be a rare mod (I can see a single picture of it on the entire internet) and it's too complex to not be done by Apple. Was is "stock" or was it a recall, idk.
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Well-known member
Do you have such a thing in your PB100 ? Its seems to be an "afterthought" set of pull down resistors (we can clearly see a common ground) to various signals
I can only say that one of the two PB100 boards I have has exactly the same fix. To me that rather looks like a factory-done fix of the suboptimal design, probably with either stability or EMC immunity/emission problems.


Well-known member
Yes so we all agree this is a factory fix, not a recall, which was one of my questions

I'll carefully check the two motherbaords I have to figure out if , maybe, they are two revision and the one without the fix maybe has those pullup resistors on the PCB
Or if they have the same revision, in which case the "patched" PB100 I have has to be superior in some way to the other.
Yeaaaah I realize this poor thing is maybe powered on 30 minutes per year now that is is retired , and that maybe what was an important fix for an expensive cutting edge business machine is completely optional for a surviving retro antique, but hey, that's the hobby to me. :ROFLMAO:

While I'm here does anyone know/have pictures of that recall they made about a problem of some pin that had to be trimmed to avoid it touching something that creates a short circuit and basically burns the laptop ? I'd rather avoid that.


Well-known member
I remember hearing about a power supply issue from back in the day that would kill the motherboard on the 100, requiring a repair to the motherboard. What chip is that thing attached to? Do we know what purpose it serves? It could be related to that issue. For what it's worth, my 100 doesn't have that, although it does appear that someone's soldered/resoldered a ceramic capacitor elsewhere on the logic board some time in the past for whatever reason. If it was a factory fix, it would invalidate that theory though.


Well-known member
I think I have the same identical mod on my machine, but executed fairly... different.

I would guess all these are pulldowns? They seem to go to GND. The mini-pcb is a nice touch on your board.


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Well-known member
AMD am85c80-8jc , multi porpose chip?


Well-known member
AMD am85c80-8jc , multi porpose chip?
Combined SCSI and Serial chip.

The datasheet you linked is for the 85C30. The 85C80 is attached. Pinout here :



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There was a long term warranty fix for the 100, it involved a bad tip on the DC power supply plug. If it chipped it shorted and destroyed the board. Happened to mine.