So I opened a used Kensington IIgs unit today and found 2 caps or varistors were damaged. Any idea what these parts are or if there is a schematic?
V3 seems to be a Z131 20UL varistor. Maybe they are all the same?
Tim
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Parts with "V_" designators on the PCB are Varistors (commonly called MOVs). They have a limited capacity for absorbing voltage spikes, then they do auto-da-fé as you saw. This is a fire hazard, so the MOVs are only recommended to be used in series with a thermal fuse. Some MOV series even integrate a thermal fuse inside their case. These "Thermally-Protected MOVs" are the ones you should consider.
They often appear in groups of 3, to provide so-called three-mode protection, against spikes between Line and Neutral, Line and Ground, and Neutral and Ground. But they are not required for operation and can be removed.
I opened up a IIgs system saver a few years back, and posted my findings here (including a schematic I reverse engineered, and no one pointed out any glaring flaws so far):
https://www.applefritter.com/content/iigs-system-saver-possible-undersized-resistors
I believe all 3 of mine were Z131 MOVs as well. None of my pictures give a great view of the markings, but I can at least make out "z131z" on one of them. According to some notes I had from back then, I must have found a datasheet for the MOVs. I had written down "steady voltage (rated at 130), amperage (12ka), energy/joules (150), and clamping voltage (340)". This seems to line up with a Z131 20UL datasheet I just found quickly.
But now that I look at your picture, yours is different than mine. The layout is not the same, and I see a big diode that is lacking from mine. Mine had a resettable circuit breaker on the back, yours has a fuse. So it looks like Kensignton revised these at one point.
For the record, here is my PCB:
Surge Protect.jpg
Wow, thanks for the great information from everyone. Since we different boards, I will also try to set up a schematic for this board and order the Varistors. One of the resistors near the blown components is pretty black so I will probably replace them with 5W parts too.