Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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isw isw is offline
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Default 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
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Default 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.


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Default 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
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Default 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.

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Default Suddenly dim LCD on "radio clock"



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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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