Suddenly dim LCD on "radio clock"

I have a La Crosse Time-Temperature device that I picked up at a garage sale about a year ago. It had a badly corroded battery compartment, which I got cleaned up, at which point the thing started working.

Recently, the display (it's one of those "big number" 7-bar LCDs) has gone quite dim when viewed head-on, but is plenty contrasty viewed at a large vertical angle. It did not have this problem when I first got it.

I know the most likely reason for that is a weak battery, but the cells checked out at about 1.5 V and replacing them made no difference.

La Crosse claims to have no schematics or other technical data at all ("the clock is made entirely in China").

Devices often have a "contrast" adjustment which changes some bias on the LCD and alters the best viewing angle, but this particular unit does not offer that as a user adjustment.

Is there some way that I can identify the particular connection to the LCD which provides this bias? If I could find it, I bet I could hack it.

thx

Isaac

Reply to
isw
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Take another look inside the device. Battery spew tends to migrate away from the point of egress, and it might not be visible. A tiny bit of stray conductance could throw the display off. The board might benefit from a good soak.

Reply to
ohger1s

I suspect this effect is due to multiplexing and an effective small intermittent DC bias , from overlaps, that somehow builds up a charge that upsets the LC

Reply to
N_Cook

You didn't say whether it was an LCD module like the HD44780 or the similar Epson units - or a glass only LCD panel with a LCD driving front panel micro.

The modules have a specific contrast pin that is easy to find on the data sheet, the glass only panels could be driven by any of a number of chips - Holtek do an extensive range. Any contrast pin could be anywhere, if its firmware defined it could be any pin on a given type of chip.

Glass only panels usually have a "zebra-strip" (rubber strip with conductive segments) making contact between glass and PCB - if the battery leaked, that could be contaminated.

Reply to
Benderthe.evilrobot

or a hammer.

Reply to
Phoena Greene

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