Larry received the second, non-functional eBay 9100B. Since the first unit worked (aside from the display anomaly), a few board swaps isolated the problem to the A1 ROM board. A little poking around isolated the problem to a single bad transistor:
HP uses weird part numbers and cross-references are rare, so Larry replaced it with a modern transistor that seemed electrically similar. It's working fine so far.
The "comet tail" display anomaly on the first 9100B was caused by the intensity being turned up too high, probably because the display is slightly dim. Here's the "fixed" display:
And here's the brighter display from the second unit:
Both units measure about 3200VDC on the display. Note that the second unit breaks numbers up into convenient groups of three...was this a feature that was rolled into production? It's a later serial number than the first unit.
9100s together!
