Viewsonic VX715 LCD

C

Chris F.

Guest
I've got two of these with the exact same symptom. The backlight cuts out
a few seconds after powering, and stays out until the the unit is turned
off/on again. There are two boards in this; the power supply, and signal
processing/CPU. I subbed the power supply board with a confirmed good one
from another unit and got the same result, ruling out that board as the
cause. Also tried disconnecting the backlight cables one at a time, but no
change. It appears that a signal from the CPU board is causing the backlight
to shut off. Is there any solution other than replacing the CPU board?
 
"Chris F." <zappyman@hotmail.com> wrote in
news:4890a3ca$0$4024$9a566e8b@news.aliant.net:

I've got two of these with the exact same symptom. The backlight cuts
out
a few seconds after powering, and stays out until the the unit is
turned off/on again. There are two boards in this; the power supply,
and signal processing/CPU. I subbed the power supply board with a
confirmed good one from another unit and got the same result, ruling
out that board as the cause. Also tried disconnecting the backlight
cables one at a time, but no change. It appears that a signal from the
CPU board is causing the backlight to shut off. Is there any solution
other than replacing the CPU board?
Click to expand...
I saw somewhere that replacing the capacitors by the HV coils for the back
light fixes the problem (this works as I have used it to fix the problem).


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But I subbed that whole board with a known good one, and it did the same
thing......
"me" <me@here.net> wrote in message
news:Xns9AEB82D7641BDmeherenet@38.119.97.3...
"Chris F." <zappyman@hotmail.com> wrote in
news:4890a3ca$0$4024$9a566e8b@news.aliant.net:

I've got two of these with the exact same symptom. The backlight cuts
out
a few seconds after powering, and stays out until the the unit is
turned off/on again. There are two boards in this; the power supply,
and signal processing/CPU. I subbed the power supply board with a
confirmed good one from another unit and got the same result, ruling
out that board as the cause. Also tried disconnecting the backlight
cables one at a time, but no change. It appears that a signal from the
CPU board is causing the backlight to shut off. Is there any solution
other than replacing the CPU board?




I saw somewhere that replacing the capacitors by the HV coils for the back
light fixes the problem (this works as I have used it to fix the problem).


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Click to expand...
 
"Chris F." <zappyman@hotmail.com> wrote in
news:4890f330$0$4033$9a566e8b@news.aliant.net:

But I subbed that whole board with a known good one, and it did the
same thing......
"me" <me@here.net> wrote in message
news:Xns9AEB82D7641BDmeherenet@38.119.97.3...
"Chris F." <zappyman@hotmail.com> wrote in
news:4890a3ca$0$4024$9a566e8b@news.aliant.net:

I've got two of these with the exact same symptom. The backlight
cuts out
a few seconds after powering, and stays out until the the unit is
turned off/on again. There are two boards in this; the power supply,
and signal processing/CPU. I subbed the power supply board with a
confirmed good one from another unit and got the same result, ruling
out that board as the cause. Also tried disconnecting the backlight
cables one at a time, but no change. It appears that a signal from
the CPU board is causing the backlight to shut off. Is there any
solution other than replacing the CPU board?




I saw somewhere that replacing the capacitors by the HV coils for the
back light fixes the problem (this works as I have used it to fix the
problem).
Click to expand...
Where do the backlights connect? Is there a seperate CCFL driver board?
All that I have seen have one, but I have not worked on a VX715...


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Is it possible that both sets of lamps are bad? How to I bypass the
protection circuit to determine if the lamps are the problem?

"bob urz" <sound@inetnebr.com> wrote in message news:1217477972_18@isp.n...
Chris F. wrote:

But I subbed that whole board with a known good one, and it did the same
thing......
"me" <me@here.net> wrote in message
news:Xns9AEB82D7641BDmeherenet@38.119.97.3...

"Chris F." <zappyman@hotmail.com> wrote in
news:4890a3ca$0$4024$9a566e8b@news.aliant.net:


I've got two of these with the exact same symptom. The backlight cuts
out
a few seconds after powering, and stays out until the the unit is
turned off/on again. There are two boards in this; the power supply,
and signal processing/CPU. I subbed the power supply board with a
confirmed good one from another unit and got the same result, ruling
out that board as the cause. Also tried disconnecting the backlight
cables one at a time, but no change. It appears that a signal from the
CPU board is causing the backlight to shut off. Is there any solution
other than replacing the CPU board?




I saw somewhere that replacing the capacitors by the HV coils for the
back
light fixes the problem (this works as I have used it to fix the
problem).


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Assuming you swapped both the main power supply board and the inverter
board with no change, you probably got worn or bad tubes.

I am dealing with a gateway 18" now with similar issues.

Most of these inverters have intelligent controller that shut down the
inverter if the lamps do not strike fast enough, are open circuit,
or draw too much current.

Without hot-wiring the protection circuits, you may not get to the bottom
of the problem.

bob


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Click to expand...
 
I dont know if your model is the same as the ones i have been working on
but i have fixed every one by replacing the one single capacitor in the
balast board
 
Chris F. wrote:

But I subbed that whole board with a known good one, and it did the same
thing......
"me" <me@here.net> wrote in message
news:Xns9AEB82D7641BDmeherenet@38.119.97.3...

"Chris F." <zappyman@hotmail.com> wrote in
news:4890a3ca$0$4024$9a566e8b@news.aliant.net:


I've got two of these with the exact same symptom. The backlight cuts
out
a few seconds after powering, and stays out until the the unit is
turned off/on again. There are two boards in this; the power supply,
and signal processing/CPU. I subbed the power supply board with a
confirmed good one from another unit and got the same result, ruling
out that board as the cause. Also tried disconnecting the backlight
cables one at a time, but no change. It appears that a signal from the
CPU board is causing the backlight to shut off. Is there any solution
other than replacing the CPU board?




I saw somewhere that replacing the capacitors by the HV coils for the back
light fixes the problem (this works as I have used it to fix the problem).


----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet
News==----
http://www.pronews.com The #1 Newsgroup Service in the World! >100,000
Newsgroups
---= - Total Privacy via Encryption =---



Assuming you swapped both the main power supply board and the inverter
Click to expand...
board with no change, you probably got worn or bad tubes.

I am dealing with a gateway 18" now with similar issues.

Most of these inverters have intelligent controller that shut down the
inverter if the lamps do not strike fast enough, are open circuit,
or draw too much current.

Without hot-wiring the protection circuits, you may not get to the
bottom of the problem.

bob


----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.pronews.com The #1 Newsgroup Service in the World! >100,000 Newsgroups
---= - Total Privacy via Encryption =---
 
On Thu, 31 Jul 2008 11:37:07 -0700, "Chris F." <zappyman@hotmail.com>
put finger to keyboard and composed:

Is it possible that both sets of lamps are bad? How to I bypass the
protection circuit to determine if the lamps are the problem?
Click to expand...
Download the datasheet for the lamp controller chip and check out the
application circuit. There should be a feedback pin that senses lamp
current. Monitor that with a scope.

Here is one example:
http://focus.ti.com/lit/ds/symlink/ucc3972.pdf

This forum suggests that the 16V 1000uF capacitors may be a common
fault with your model:
http://www.aplusperfect.com/articles/lcd_capacitor_repair

Maybe the "known good" PSU is only marginally good and has trouble
striking your worn lamps ???

As a matter of course I would reflow all the solder joints at the
transformers and coils.

"bob urz" <sound@inetnebr.com> wrote in message news:1217477972_18@isp.n...
Chris F. wrote:

But I subbed that whole board with a known good one, and it did the same
thing......
"me" <me@here.net> wrote in message
news:Xns9AEB82D7641BDmeherenet@38.119.97.3...

"Chris F." <zappyman@hotmail.com> wrote in
news:4890a3ca$0$4024$9a566e8b@news.aliant.net:


I've got two of these with the exact same symptom. The backlight cuts
out
a few seconds after powering, and stays out until the the unit is
turned off/on again. There are two boards in this; the power supply,
and signal processing/CPU. I subbed the power supply board with a
confirmed good one from another unit and got the same result, ruling
out that board as the cause. Also tried disconnecting the backlight
cables one at a time, but no change. It appears that a signal from the
CPU board is causing the backlight to shut off. Is there any solution
other than replacing the CPU board?

I saw somewhere that replacing the capacitors by the HV coils for the
back
light fixes the problem (this works as I have used it to fix the
problem).

Assuming you swapped both the main power supply board and the inverter
board with no change, you probably got worn or bad tubes.

I am dealing with a gateway 18" now with similar issues.

Most of these inverters have intelligent controller that shut down the
inverter if the lamps do not strike fast enough, are open circuit,
or draw too much current.

Without hot-wiring the protection circuits, you may not get to the bottom
of the problem.

bob
Click to expand...
- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
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