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From: JW on 5 May 2010 05:41
Working on a Keithley 580 micro ohm meter that has a display problem. The
first row which controls the bottom segments is very faded - the more
segments that are lit, the more faded they are. I've already used alcohol
to clean the two zebra strips, PCB and LCD itself. I've tried re-orienting
the zebra strips to see if the problem moves; it does not. Checked the
UPD7225 driver chip - pin 17 (COM2) drives this row, it is working fine. I
believe that either the LCD itself is defective, or perhaps the conductor
on the glass is partially open/high resistance. If the latter (and I'm
hoping this is the case) has anyone ever had this sort of problem, and
perhaps tried one of those conductive pens to repair the fault?

Thanks.
From: N_Cook on 5 May 2010 06:46
JW <none(a)dev.null> wrote in message
news:one2u55tiglr51e0on1ljka77agvneon2r(a)4ax.com...
> Working on a Keithley 580 micro ohm meter that has a display problem. The
> first row which controls the bottom segments is very faded - the more
> segments that are lit, the more faded they are. I've already used alcohol
> to clean the two zebra strips, PCB and LCD itself. I've tried re-orienting
> the zebra strips to see if the problem moves; it does not. Checked the
> UPD7225 driver chip - pin 17 (COM2) drives this row, it is working fine. I
> believe that either the LCD itself is defective, or perhaps the conductor
> on the glass is partially open/high resistance. If the latter (and I'm
> hoping this is the case) has anyone ever had this sort of problem, and
> perhaps tried one of those conductive pens to repair the fault?
>
> Thanks.

How many backplanes does it use?
ie comparing total number of segments and active pins.
Discover which backplane controls that line , via 50Hz sig gen or similar
and trace a problem on that line


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://diverse.4mg.com/index.htm



From: JW on 7 May 2010 09:16
On Wed, 5 May 2010 11:46:27 +0100 "N_Cook" <diverse(a)tcp.co.uk> wrote in
Message id: <hrri7p$6t3$1(a)news.eternal-september.org>:

>JW <none(a)dev.null> wrote in message
>news:one2u55tiglr51e0on1ljka77agvneon2r(a)4ax.com...
>> Working on a Keithley 580 micro ohm meter that has a display problem. The
>> first row which controls the bottom segments is very faded - the more
>> segments that are lit, the more faded they are. I've already used alcohol
>> to clean the two zebra strips, PCB and LCD itself. I've tried re-orienting
>> the zebra strips to see if the problem moves; it does not. Checked the
>> UPD7225 driver chip - pin 17 (COM2) drives this row, it is working fine. I
>> believe that either the LCD itself is defective, or perhaps the conductor
>> on the glass is partially open/high resistance. If the latter (and I'm
>> hoping this is the case) has anyone ever had this sort of problem, and
>> perhaps tried one of those conductive pens to repair the fault?
>>
>> Thanks.
>
>How many backplanes does it use?
>ie comparing total number of segments and active pins.
>Discover which backplane controls that line , via 50Hz sig gen or similar
>and trace a problem on that line

Um, there is no problem on the signal, the signal is fine. I'm wondering
if the traces on the LCD where the zebra strip connects can be repaired
with a conductive paint, or whether I'll just make things worse by trying.
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