Fluke 744 Display

[Tommy_T]

Hi folks
I recently got my hands on a Fluke 744 but the display Contrast isn't working correctly.
It fades after a few seconds the device is still working.
So im looking for the schematics to check if some voltagerails is breaking down.
It makes no difference if i power the device from batteries or external power source.
LC displays are not my special field so i hope for some clues from the forum.
I also made a video of the behavior:  https://youtu.be/-CaztCxyu7I
Pics: https://imgur.com/a/vczUywI

The lcd PCB gets driven from an Epson S1D13305F00B1
The Display gets driven of 6 samsung s6b2086x01

Thanks Thomas

[byte]

You haven't mentioned whether you have probed anything yet. I would work backwards probing from the LC display until I find out where the drop in display voltage/current is coming from. Could be the driver ICs, could be a voltage regulator feeding the IC, or something else. I didn't look at the datasheets on these ICs, but one of the ICs/regulators may have thermal or overcurrent protection built-in. If so, then once you isolate the device you can check for downstream from it for unexpected low impedances and start probing back to the LCD. Assuming excessive current draw, it could be coming from anything such as an electrolytic cap that is aging or something as simple as a barely bridging solder joint and/or excessive flux that after enough time has started to cause excessive current leakage.

I'm no expert with LC displays either, just my 2 cents.