41C is ON, display is OFF, a key pressed display is ON --Repair Help

[TallKey]

Reviving a HP-41C, it is a very clean early low key Fullnut.

It needed the battery film replaced (replacement is from Diego). The circuit board gold traces look near new, zebra is in great shape, the posts and screw wells are in great shape.

Have used a 8x loupe to check for lint/dust at IO film and zebra strip.

Ohm meter checked some of the zebra to circuit endpoints and they checked 0.2-0.4 OHMs.

Hopeful someone has some good guesses/guidance to help repair this beauty. Fingers crossed it is not "your display driver has failed."

It powers ON and all keyboard keys test good. The key presses work normally, until the key is released and the display blanks. IE press 8 and see 8, release the 8 key and the display blanks. Press 8 multiple times it fills the mantissa, but releasing the 8 key and the display blanks.

More of the same:
CLX ON
MEMORY LOST (displayed briefly), then a blank display.

Press the TAN key, TAN is displayed followed by NULL, release the TAN key and the display blanks. Same behavior for all keyboard keys.

PRGM, ALFA and USER cause the display to display normally, then releasing the key causes the display to blank. ALFA and PRGM modes appear to work normally. The ON key turns it OFF.

All display segments appear to work, did not test the colon ":" key.


Have swapped spare 41c logic boards, same as above.

Thanks!