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 |
Suddenly dim LCD on "radio clock"
On Thursday, February 16, 2017 at 12:00:25 AM UTC-5, isw wrote:
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 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. |
Suddenly dim LCD on "radio clock"
On 16/02/2017 05:00, isw wrote:
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 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 |
Suddenly dim LCD on "radio clock"
"isw" wrote in message ... 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. 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. |
Suddenly dim LCD on "radio clock"
wrote in message ... On Thursday, February 16, 2017 at 12:00:25 AM UTC-5, isw wrote: The board might benefit from a good soak. or a hammer. |
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