Help: HP9825A Power Up Issue

[John M (Ottawa)]

I acquired HP9825A from a friend and I am trying to bring it to life. It was in storage for many years and is in good condition. When I power up, I get flashing display - alternating between cursor and full-segment display (all pixels on). Pressing any key results in flashing to change between "error 01" and full-segment display. Pressing RESET clears the error code but returns to previous flashing state. There are no ROM cards or interfaces installed. I checked the Operating System module is clean and appears to be properly seated. Any help is appreciated.

[Steve Leibson]

Error 01 is an "unexpected peripheral interrupt." A basic 9825 has three peripherals: keyboard, display, tape. Check the keyboard for a stuck-down key. The "enter" key was used the most, so check it first. If this is an earlier model with the clicky calculator-style keys (as opposed to the later computer-style keys) then one of the key contacts may have stuck down.

[Tony Duell]

My immediate thought is that it's power supply trouble. Given the machine has been in storage, I would suspect dried-up capacitors causing excessive ripple on the supply lines. A machine with supply lines that are dipping below the expected value twice every mains cycle is going to behave oddly :-)

You can get the service manual ('boardswapper guide') and schematics from the Australian museum site. Start by using a 'scope to check every supply line for the correct voltage and lack of ripple. If you find any problems, check the electrolytic capacitors on the PSU board.

[John M (Ottawa)]

Thank you for the suggestions.

1. Steve - No stuck keys.
2. Tony - Power supplies voltages look OK. Not much ripple on the few lines I checked. (Thanks for the schematics).

Upon further experimentation, the 9825A works OK with a tape inserted in the tape drive. I was initially reluctant to insert a tape since the drive's capstan wheel is obviously gummy. But when I insert a tape, the "error 01" resets. Eject the tape - I get the error 01 when any key is pressed.

Alas, now my big decision - rebuild the tape drive or not?

[Dave Shaffer (Arizona)]

Quote:

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rebuild the tape drive or not?

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For the moment, can't you hot wire a switch somewhere (mechanical or electrical "tape detect" it would seem)?