Suddenly dim LCD on "radio clock"

[isw]

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

 

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.

 

[N_Cook]

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

 

[Benderthe.evilrobot]

"isw" <isw@witzend.com> wrote in message
news:isw-8B040A.21001515022017@news-roam.garlic.com...

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.

 

[Phoena Greene]

<ohger1s@gmail.com> wrote in message
news:922680d8-09cd-4309-8fa8-7b746ac25df8@googlegroups.com...

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.