The HP-33E has two versions that I am familiar with. Both have a large CPU chip; one has three, the other has two support chips. One of the support chips, marked IMA104, is shared between the two models. This chip was dead in one of my HP-33Es; its failure, in turn, caused overload and eventual failure of the calculator's DC-DC converter circuit. Since the overload-induced failure was not immediate, it was possible to identify the faulty chip by installing it in an otherwise working HP-33E.
Bad chip in HP-33E
