Sony SDM-HS74P 17" TFT 'two seconds to black'

[Fest911]

Hello

I cam across the following posting while trouble shooting the sam
problem with the same monitor
http://www.jlaforums.com/viewtopic.php?p=1999382

The raster comes on for about 2 seconds and then goes black. I don'
have the equipment to ESR the caps, so I checked for anythin
obvious and then checked the two two high voltage outputs CW401, 402
They are identified on the board as 800Vac 15mA max. I measure
these with an AC meter and came up with one side at about 230v an
the other was almost 10x that, at 2.2kv

The funny thing is that when my test leads are across the highe
output, the raster comes on and stays on as long as my meter i
connected. As soon as I remove a test lead, the raster shuts off

Testing the side with 230v doesn't make a difference. The raste
stays on just long enough for my meter to capture the voltage

I assume my power board (6871TPT285A) is no good, and will order
replacement (superseded to 6871TPT286A), but I'm wondering if i
makes sense to anyone that the raster stays on when my meter i
connected to the output that is reading high

Thanks for your input
Best
Mat

 

[Baron]

Fest911 Inscribed thus:

Hello,

I cam across the following posting while trouble shooting the same
problem with the same monitor:
http://www.jlaforums.com/viewtopic.php?p=19993827

The raster comes on for about 2 seconds and then goes black. I don't
have the equipment to ESR the caps, so I checked for anything
obvious and then checked the two two high voltage outputs CW401, 402.
They are identified on the board as 800Vac 15mA max. I measured
these with an AC meter and came up with one side at about 230v and
the other was almost 10x that, at 2.2kv.

The high voltage suggests that there is no load on the output of the
inverter transformer. Could be O/C series cap or a failed tube.

Not to long ago I posted some pictures of a failed cap on an inverter
board. Replacing the cap solved the problem.

The funny thing is that when my test leads are across the higher
output, the raster comes on and stays on as long as my meter is
connected. As soon as I remove a test lead, the raster shuts off.

Testing the side with 230v doesn't make a difference. The raster
stays on just long enough for my meter to capture the voltage.

I assume my power board (6871TPT285A) is no good, and will order a
replacement (superseded to 6871TPT286A), but I'm wondering if it
makes sense to anyone that the raster stays on when my meter is
connected to the output that is reading high?

There is probably a current sensing circuit that now thinks that the
load is OK.

Thanks for your input!
Best,
Matt

--
Best Regards:
Baron.

 

[Jamie]

Baron wrote:

Fest911 Inscribed thus:


Hello,

I cam across the following posting while trouble shooting the same
problem with the same monitor:
http://www.jlaforums.com/viewtopic.php?p=19993827

The raster comes on for about 2 seconds and then goes black. I don't
have the equipment to ESR the caps, so I checked for anything
obvious and then checked the two two high voltage outputs CW401, 402.
They are identified on the board as 800Vac 15mA max. I measured
these with an AC meter and came up with one side at about 230v and
the other was almost 10x that, at 2.2kv.


The high voltage suggests that there is no load on the output of the
inverter transformer. Could be O/C series cap or a failed tube.

Not to long ago I posted some pictures of a failed cap on an inverter
board. Replacing the cap solved the problem.


The funny thing is that when my test leads are across the higher
output, the raster comes on and stays on as long as my meter is
connected. As soon as I remove a test lead, the raster shuts off.

Testing the side with 230v doesn't make a difference. The raster
stays on just long enough for my meter to capture the voltage.

I assume my power board (6871TPT285A) is no good, and will order a
replacement (superseded to 6871TPT286A), but I'm wondering if it
makes sense to anyone that the raster stays on when my meter is
connected to the output that is reading high?


There is probably a current sensing circuit that now thinks that the
load is OK.


Thanks for your input!
Best,
Matt


If this is a LCD panel with CCFL, it could be that one or more of the

tubes are out and it's not detecting proper load, and shutting down..

Or , could just be a bad inverter as you say..

 

[Meat Plow]

On Sun, 09 May 2010 01:36:45 -0500, Fest911 wrote:

Hello,

I cam across the following posting while trouble shooting the same
problem with the same monitor:
http://www.jlaforums.com/viewtopic.php?p=19993827

The raster comes on for about 2 seconds and then goes black. I don't
have the equipment to ESR the caps, so I checked for anything obvious
and then checked the two two high voltage outputs CW401, 402.
They are identified on the board as 800Vac 15mA max. I measured
these with an AC meter and came up with one side at about 230v and the
other was almost 10x that, at 2.2kv.

The funny thing is that when my test leads are across the higher output,
the raster comes on and stays on as long as my meter is connected. As
soon as I remove a test lead, the raster shuts off.

Testing the side with 230v doesn't make a difference. The raster stays
on just long enough for my meter to capture the voltage.

I assume my power board (6871TPT285A) is no good, and will order a
replacement (superseded to 6871TPT286A), but I'm wondering if it makes
sense to anyone that the raster stays on when my meter is connected to
the output that is reading high?

Thanks for your input!
Best,
Matt

The inverter is about twice the voltage needed. Maybe you have a CCFL tube
or connection problem?

 

[Franc Zabkar]

Here is the service manual. I don't think it helps, though. :-(

COLOR MONITOR SERVICE MANUAL
CHASSIS NO. : CL-42
FACTORY MODEL: LHS74P, LHS74PM
MODEL: SDM-HS74, SDM-HS74P

http://archive.espec.ws/files/SDM-HS74P%20KRSVM000081483.pdf

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