HP-46/81 Case, Power Supply

[Duane Hess]

Swapped all the 46 keyboard, display card, printer, mother board from the unit and installed the 81 stuff (buffered keyboard). Turned the unit on, the busy LED went on solid & nothing would happen other than the printer motor would turn accordingly to the PRINT OFF key.

Both the 46 and 81 cards have the BUSY LED and the full numeric digit display. ... think its Option 1 on the 46 and Option 3 on the 81.

Installed the 46 display card, same results, coincidentally noticed if powered off unit & turned in back on in about 1/2 second it would operate. Reinstalled the 81 buffered keyboard display, had issues, memory recalls would not work right. Printing was spazzy. Seemed to randomly work OK, overprint, omit positions, etc. Reinstalled the 46 display card as it seemed to work better. But I'm quite sure that was coincidence.

Would need to go check my notes. The +6, -12 and +15 VDC test points were within the voltage variations on the 46. After swapping in the 81 parts those were OK, except for the +15VDC was 13.somethingVDC.
[EDIT] The voltage tolerance values were from the 9805 service manual as I didn't noticed reference to tolerance levels in the 46/81 manual.

Noticed the HP46 Printer Repair Tip on the museum which describes spastic printing behavior. However, nothing it seems to describe the LED lockup upon power on. Also it seemed when the buffered keyboard display was installed recall of memory registers intermittently would fail with flashing 9.99999999E99.

Any suggestions would be welcome. Definately will be some time before repair should the problem be the capacity mentioned in the Printer Repair Tip article.