plasma tv out of service

[takara]

hello,

I own a plasma tv which does not work now . the sound is ok but display is dark like a photographic film. I found the -Vy voltage in the Y-sustain board has between 0 and -6 volt. I heard this problem could be provoked by the inverter into the board.

I will appréciate some help to fix this failure.

[tom66]

Re: plasma tv out of service

Can we see a picture of the problem?

[takara]

Re: plasma tv out of service

hello,

I can send a picture of the probleme. I forgot to announce the model of my TV plasma : PDP42V7

regards,

[tom66]

Re: plasma tv out of service

That does look a little like low -Vy might cause that. -Vy can sometimes be brought down by a bad buffer board.

[takara]

Re: plasma tv out of service

hello Tom66,

thank you for your reply. you suggest to check the buffer board but I do not kown where is it located on the tv.As I said previously, I read a book which shows an inverter producing this famous -Vy voltage. This inverter is surrounded by a optocopler, transistor an IC model NCP1200D6 and 4 condensators.

[tom66]

Re: plasma tv out of service

Can we see a picture of the boards in your TV. I will highlight the buffer board.

[takara]

Re: plasma tv out of service

please find below the picture showing the boards of the tv.

[takara]

Re: plasma tv out of service

I read the specifications indicated behind the screen : the -Vy voltage must be at -95 volt.
I've made also some measurements with the vsc, va and vs which are OK.

[tom66]

Re: plasma tv out of service

On your panel the buffers are on the left of the image. It's the boards that connect to the Y-sus where you measure the -Vy etc.

[takara]

Re: plasma tv out of service

Hello tom66,

I have disconnected the buffers from the Ysys board but the Vy voltage is still the same (between 0 and 8 volt). it is not stable. Normally the specification for that is -95 volt.

In addition, I've forgot to tell you there is 0 volt at the Vsetup voltage. Normally the specification for that is 183 volt.

[tom66]

Re: plasma tv out of service

You probably have a short somewhere on your board bringing down those voltages, but locating that will be tricky.

[takara]

Re: plasma tv out of service

I noted that I heard a noise (Bzzzz) every 2 or 3 seconds near or under the IPM heatsink.
The IPM could be in short circuit even if the fuse is not blown ?

[tom66]

Re: plasma tv out of service

That is possible, we have heard of buzzing IPMs before being dead.

[takara]

Re: plasma tv out of service

thanks Tom66


Could I disconnect the control board connector from the Ysus board to test if I note some changes ?

[tom66]

Re: plasma tv out of service

I'd expect no image at all...

[takara]

Re: plasma tv out of service

you right !

I also wondering if the 2 mosfets STP9NK70ZFP which are attached with screw can bring down the Vy and Vsetup voltage. I cannot test them directly on the ysus board. I have to desolder them before.

[tom66]

Re: plasma tv out of service

Where are they, can you highlight them on a photo?

[takara]

Re: plasma tv out of service

hello

yes I can highlight the 2 mosfets on the attached picture. There are located on the left hand side.

Yesterday I made a mistake. I wanted to test the resistor R4 but I did a short circuit. The lead of my multimeter has touch one of the leg of this standard resistor R4 and the other leg of a cms resistor. A short circuit appeared and the 2 resistors became black. The tv switch off (stand by mode) automatically as a security position .

The value on these resistor is still OK but now they are black

Is the Ysus board out of service now because of this short circuit ?

[tom66]

Re: plasma tv out of service

I suspect it had a fault previously, so you have only made it a little worse -- unfortunately, due to the lack of schematics for these boards, you may be stuck with trying to find a replacement board. The cost of repair may exceed the cost of a replacement.

[takara]

Re: plasma tv out of service

hello tom66,

I have replaced the ipm but the problem is still there : no Vy voltage. In addition, there is no Vs voltage on the resistor R14 (please see the diagram attached).

do you have any idea ?
thanks