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

[TallKey]

(02-14-2023 03:55 AM)Didier Lachieze Wrote:  According to this thread, this could be due to a defective display driver:

Quote: From page 7 of the service manual's updated service notes (HP41C-35)

4. Display lit only when a key is pressed (blanked in standby).

a. Replace display driver hybrid. (P/N 00041-60090)

Thanks for reminding me of the this part of the service manual.

The service module gave me hope, but reading the service manual 2-57 (p2-12) probably means the module avoids STANDBY mode by keeping the display ON (PWO high).

Standby Test (p4-17). Any change in the display indicates that the display driver, oscillator capacitor (C2), or CPU is bad. Initiate Standby Test, display goes OFF, pressing any key, display ON, then STANDBY OK is displayed. C2 being bad on 2 CPU boards seems unlikely.

Service module installed, all the tests I can perform test OK but for the Standby Test. Standby test is supposed to cause the display to remain ON (it stays on when tested on the CV).

Too tested the contacts "Figure 4-5 keyboard PC board", service manual. Checked all 59 pads, with the zebra connector installed, 0.2 - 0.4 OHMs.

Have not attempted to retouch the solder contacts. They all look good and they feel solid.

The driver is the type with grey epoxy covering the 2 ICs. It is my understanding not any Fullnut display driver will work as a replacement. Is that correct?

See photo to date the display at hand.

I do not want to give up on this and part it out. It is physically in minty condition (the quad memory module needs a home).

If I had a known compatible & working display driver, I'd replace the driver.