Agilent/Keysight U1242A LCD contrast issue

[NilsRoe]

Hi,

a colleague found a seemingly dead Agilent U1242A in the junk bin at work. It is still working, however the LCD is barely readable. The contrast is very weak, and it can only be read when holding it at the right angle. The backlight works fine. The LCD reads better with fresh batteries, thoug it is still barely legible.

Is there a hidden contrast setting, a trimmer, or some component that is known to cause the issue? I have already tried cleaning up the LCD, the zebra strip and the contact pads on the PCB; to no avail. I do not have much spare time anymore to investigate these things, so if there's someone out there who has had a similar issue with a U1242A please let me know.

Best regards,
NilsRoe

[MosherIV]

Hi

Before you spend money, try holding up some polarized sun glasses to see if it improves the contrast.

I found this utube video which explains why and possibly where to get replacement polarizing film.



Good luck

[NilsRoe]

I just took it apart again; the panel itself seems to be fine. I tested it with a coin cell battery, carefully running a finger along the zebra strip. All the segments turn on, very sharp and crisp. So I guess it has something to do with the main PCB.

[NilsRoe]

I have measured some of the contact pads with my oscilloscope; I'm reading a fairly typical 3VAC square wave with some modulation. Do the contact srips break down after a while? I haven't seen this kind of failure before. The contact strip measures arount 1K Ohm from top to bottom, so it should be allright.