HP 9872T Trouble Shooting

[cruff]

(06-10-2018 08:05 PM)husmann Wrote:  [2.23.g] The Self Test LEDs will flash sequentially as a lamp test. Total failure here: each and every self test LED stays off.

This means the BPC microprocessor is not executing instructions properly. Do you have an oscilloscope or logic analyzer available to help with the diagnosis? Fortunately the logic levels should all be 5 V.

If ROMs U55 and U56 are socketed, try reseating the ROM chips. Perhaps some pin/socket contact oxidation is interfering.

Can you observe the clock signal at pins 5 and 6 of clock divider U60? They should be 5 MHz with alternating levels.