HP8925A - Continuous BEEP and garbage display

[mark stephens]

I picked up an non-working 8925A with a dozen tapes, a HPIB interface and a BCD or Parallel interface for $10!

I found a cracked chip on the Display controller CMOS bottom left CD4001UBE and replaced it.

However, Now, when I turn on, all the Display characters are lit up and the calculator beeps continuously.

Any ideas? Please don't tell me the OS cartridge is cactus!

--marki

Edited: 29 July 2013, 12:04 a.m.

[Rik Bos]

I suppose you mean a HP 9825A.

First thing to is check all the supply voltages, the 9825 doesn't have a crowbar, and you don't want to see what's happening if the main switching transistor in the PSU shorts. It is a switching PSU so be careful not to run it with out a load.

Next thing check all the wiring and connectors PSU board connectors have a tendency to crack, resulting in parts of the machine not getting the right voltages.

Next thing try to get the schematics of the 9825, they are on the HPCC diagrams CD made by Tony.

Check if the ram boards are configured the right way, you can find that in the service manual. You also can interchange them if you reconfigure the boards, if you have more then one board, check if the machine will run with only one at a time.

Remove the tape controller board and printer and tape connection to see if there is a problem.

If it's not working now you have to check the control signals like the clock and data signals.

-Rik

[mark stephens]

Rik, Where abouts do the PSU PCB have a tendancy to crack?

[Rik Bos]

The connector for the PSU board has a tendency to crack if the boards are under tension or aren't placed well.

-Rik