Samsung plasma PA43H4900 not turning on.

[Josedas]

Hi Everybody,
I returned home after a trip to native town only to discover my TV wont turn on. There was heavy rain and storm for few days. same thing happened to few of my neighbors too.
The standby light on the bottom left corner was blinking randomly.
Opened the TV and tested for voltages. Zero voltage readings on the Va and Vs points. led on the logic board too blinking randomly.
The power supply has 2 connectors. one connects to the 'X main' and the other to the main board. The power to 'Y main' is taken from the 'X main' board. Please see the attached image.
First I disconnected the connector from SMPS to X main and switched on the TV and nothing happened. No LED light or anything. So connected it back and disconnected the X main to Y main connector and checked again. Now there is correct voltage available on VS and VA, but is not sustained. Dropping off slowly to zero, again coming on and dropping off.
Then I removed both connectors from power supply board and shorted ps_on to ground and vs_on to 5V.
Now there are correct voltages available on all the pins. Vs reading 211V and Va reading 58V.
Does this mean the power board is fine? what if the Voltage is present only because, no load is connected?
If SMPS is fine, what else could have failed?
I am at a dead end here and desperately need some help.
Thanks in advance.

[Andrew F. Ali]

Re: Samsung plasma PA43H4900 not turning on.

Did you load the VS when you shorted ps_on to ground and vs_on to 5V?

[Josedas]

Re: Samsung plasma PA43H4900 not turning on.

Hi, thanks for the reply.
No. There is no load on Vs. All connectors are removed from PSU. Can you explain me how to load the Vs?

[Josedas]

Re: Samsung plasma PA43H4900 not turning on.

Hi, I tested the PSU connecting a 100 watts incandescent bulb at VS and it glows steadily. So if the PSU is healthy, then what could have failed. I get 5 double blinks of led on the logic board at power up, then nothing. What's the probability of panel failure.
I could use some help here dear members.. Thank you.

[dick_barton]

Re: Samsung plasma PA43H4900 not turning on.

With two 100W incandescent lamps connected in series they should stay nice and bright. You can then check what voltage you have for Va & Vs and if they match what's given on the label on the panel.

[Andrew F. Ali]

Re: Samsung plasma PA43H4900 not turning on.

With the incandescent bulb glowing bright and steady measure VA and the rest of other voltages to ensure ALL the voltages are being produced by the PSU Also take note that the VS would be 185~205Vdc therefore if the incandescent bulb you are using is not rated at 230V you would have to put two (2) 120V bulbs in series to connect to the VS.

[Josedas]

Re: Samsung plasma PA43H4900 not turning on.

The sticker on the panel mentions 210V and 58V for VS and VA respectively. Connected a 230V 100W bulb on Vs and it glows bright and steady. Same time VS is measured 211V and VA 58V. All other 15V and 5V pins are reading correctly.

[dick_barton]

Re: Samsung plasma PA43H4900 not turning on.

So it looks like the power supply is working correctly. With the power to the set off measure the resistance from Va to chassis and Vs to chassis and give the readings.

[Josedas]

Re: Samsung plasma PA43H4900 not turning on.

So it looks like the power supply is working correctly. With the power to the set off measure the resistance from Va to chassis and Vs to chassis and give the readings.

Hi, thanks for the lead,
measured the Vs resistance and got 0.6 ohms and Va returned about 10K ohms.
So the Vs looked grounded and traced it to a shorted igbt on the Y-main board. It's marked 30J127. Pictures attached. Will replace it and see.
Thanks.

[Andrew F. Ali]

Re: Samsung plasma PA43H4900 not turning on.

If you find one (1) of the IGBTs shorted, as a precaution I would recommend changing all of them as the other seemingly good ones would have taken load also and would fail with time to produce a repeat failure.

[Josedas]

Re: Samsung plasma PA43H4900 not turning on.

If you find one (1) of the IGBTs shorted, as a precaution I would recommend changing all of them as the other seemingly good ones would have taken load also and would fail with time to produce a repeat failure.

Hi, thank you. Will try to do that.

[Josedas]

Re: Samsung plasma PA43H4900 not turning on.

Hi, I have my TV working again. Replaced the y-main and it sprung to life.
Thanks a ton to this community and specially to dick_barton, andrew_ali for the help.