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Sunday, May 2, 2021

CONTINUITY: HP 9825 Repair Part 6: Can the HP 547A Probe Get Us Out of Trouble?

As analysis progresses of the damage done to a 1970s vintage Hewlett-Packard (H-P) 9825 laboratory computer by a single shorted transistor in its power supply, one of the worst nightmares in digital circuitry debugging manifests itself: a stuck bit in an on-board bus. The stuck bit could be due to any of the numerous components on the bus, all soldered in place. To deal with this problem, in the 1970s, H-P introduced a piece of test equipment, the HP 547A current tracer. The idea was that by sensing the magnetic field of current flowing to the fault in the circuit, it would be possible to localise the fault on a bus with many components attached. Can this H-P gadget diagnose the fault in this H-P computer?

Posted at May 2, 2021 11:57