A long-standing rumor about a rare Macintosh bug has finally proven true

Apple is known for the incredible attention to detail it puts into the design and construction of its products. But every now and then things happen – for example, when the Macintosh LC III was released in 1993, it actually had a fault on the motherboard, but for years no one could confirm the fault. Until now.

Doug Brown, a vintage Mac enthusiast, recently posted on his blog about restoring a Macintosh Performa 450, which is a repackaged Macintosh LC III. While replacing the original capacitors on the motherboard, Brown discovered that one of them was installed incorrectly because the positive and negative terminals were incorrectly labeled.

It turns out that Brown participated in a forum discussion about this issue back in 2013, but no one could confirm that this was an Apple error. However, after seeing the problem on the Performa 450 and the correct alignment on other Macintosh LCs, Brown believes that the screen printing marking the connector on the Performa 450/LC III motherboard was faulty.

So why were these Macs still working and why didn’t Apple fix the problem? According to Brown, the incorrectly installed capacitor had a voltage rating of 16V, but was only running at -5V, which could have been enough to cause failure but not explode or catch fire. In addition, it was only used for the serial port and expansion cards, which owners of this type of Mac were unlikely to use.

Doug Brown

Brown wanted to draw attention to this because many computer restoration hobbyists replace old electrolytic capacitors with tantalum capacitors, which are “not quite as forgiving when installed upside down.” So if you are restoring an old LC III, be sure to install the capacitor the right way up.