Larry Pina describes the addition of a resistor-array at location D-15 on the original 128K logicaboard to prevent a random bug where the Mac simply locks up. This is in the section where he is describing the 512K RAM upgrade, so I always thought it was related to the upgrade. I have seen a large number of 512K upgrades to the original board and have seen this resistor, however I've not seen many original 128K boards with this added resistor-array. Of the ones I've seen, they all look extremely professional, but then so do some of the 512K RAM chip upgrades.

When did Apple realize they had a problem, and was this resistor array added at the factory or was it only added by authorized service providers? Was there a recall, or did the Macs just get upgraded when they consistently failed on a customer who finally brought it in for service?

Here's a pic from a current eBay auction, note the yellow resistor-array at D-15 soldered onto the side of the 6522 VIA chip.