HP-19C Repair Odysee

[teenix]

(07-06-2021 11:19 AM)Artur - Brasil Wrote:  Well, I checked again the voltages. All are there, but nothing on display.
I checked again and it seems to me that, as I tested display using + probe at left and - at right, the voltages of left should be more positive than right, but my measuring on real circuit shows the inverse!
I'll try again, but I'll give some time. I have other things to work in home...

Many thanks Tony, Teenix, Bernhard, Panamatik. I really like to have the opportunity to learn with you!

Sincelrely best wishes from Brazil !
Artur

Check that pin 10 for 1820-1620 (cathode driver) is definitely grounded. This is the return path for all the LED segments.

If you have a 1K5 resistor on hand perhaps for a temporary connection:

VCC -> Resistor -> single LED anode

Taking care not to short any pins, briefly touch the resistor end to any LED anode pins (one at a time) on the 1818-0432 (pin 1 or 2 or 3 or 4 etc). If you can reach the display better, then any of the anode pins (I think display pins 1, 2, 3, 4 etc)

This should show the same LED segment on for all digits (probably dimly). If so, then the LEDs work and the cathode driver is working. If not, it might suggest the cathode driver or connectors PCB traces etc might be faulty.

cheers

Tony