There have been some past rumblings on the internet about a capacitor being installed backwards in Apple’s Macintosh LC III. The LC III was a “pizza box” Mac model produced from early 1993 to early 1994, mainly targeted at the education market. It also manifested as various consumer Performa models: the 450, 460, 466, and 467. Clearly, Apple never initiated a huge recall of the LC III, so I think there is some skepticism in the community about this whole issue. Let’s look at the situation in more detail and understand the circuit. Did Apple actually make a mistake?
↫ Doug Brown
Even I had heard of these claims, and I’m not particularly interested in Apple retrocomputing, other than whatever comes by on Adrian Black or whatever. As such, it surprises me that there hasn’t been any definitive answer to this question – with the amount of interest in classic Macs you’d think this would simply be a settled issue and everyone would know about it. This vintage of Macs pretty much require recaps by now, so I assumed if Apple indeed soldered on a capacitor backwards, it’d just be something listed in the various recapping guides.
It took some very minor digging with the multimeter, but yes, one of the capacitors on this family of boards is soldered on the wrong way, with the positive terminal where the negative terminal should be. It seems the error does not lie with whomever soldered the capacitors on the boards – or whomever set the machine that did so – because the silkscreen is labeled incorrectly, too. The reason it doesn’t seem to be noticeable problem during the expected lifespan of the computer is because it was rated at 16V, but was only taking in -5V.
So, if you plan on recapping one of these classic Macs – you might as well fix the error.