PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

[noledud]

Hi all got this set with just clicking, found burnt out z-main so got a repair kit as boards are not about

now the set powers up with correct voltages on ps and i can see the VR-VSC and VSCH jumping around on the y-main so is that now working ?

my question is how can i trouble shoot now to find the fault my basic knowledge can only get me this far.

thanks all

[tom66]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

Disconnect Y-buffer, if Vsc/etc come back, this indicates a shorted/bad Y-buffer (it's common these for the buffer to be damaged by the X-main somehow, not sure how.)

[noledud]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

hi tom i have vcs and va power is up

[noledud]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

should the voltages on the test points VR-VSC and VSCH on the y-main be jumping around ?

[noledud]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

anyone ?

[freakaftr8]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

like Tom said if you have a shorted buffer board anything that looks odd can be driven from bad buffers.
did you disconnect buffer board and then get these readings or was this with the buffer board still connected?

[noledud]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

sorry that was with buffers

so with i get the VR-VSC and VSCH jumping around

without the buffers out they are dead 0v

[freakaftr8]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

I'd say buffer shorted If vsch and -vy are dead with it installed also.

[tom66]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

Check Vsc/Vsch just as set powers up - they might go to the correct values then drop out.

[noledud]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

sorry had duff readings changed batt in meter and now


VS 208
VA54

VSC -110
VSCH - jumps from 80 to 110

without buffers

vs 208
va 54

vsch -36.8
vsc -193

[noledud]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

so are they the expected readings does that mean the buffers are dead ?

[tom66]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

That suggests potentially bad buffers. To be sure, check using this test:
https://www.youtube.com/watch?v=51SZsfH60EY

[noledud]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

will check and come back thanks tom and freak

[playgoods]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

I have one of these tv sets that is faulty. There is a blown mosfet 19NF20 on the Y Buffer board.
Is it worth it to try and replace just the fet? All voltages are correct with the Y Buffer board disconnected

[satinser]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

I also have a problem with this model similar to original poster Noldud. In this case Ysus was confirmed bad with usual failed Fets. Ohms kit 275 was fitted so all the shorted components were replaced. The instruction with the kit stated that if pads of SMD resistors R5040, R5044 and R5045 were shorted to ground this would indicate that U5008 and U5011 (T541 SSOP20 ICs) had also failed and should be replaced but this is supposed to be a rare occurrence. So rare that their not included in the kit and had be obtained separately. I found that in this case the pads were indeed shorted to earth so 2 T541 ICs were also fitted. This cleared the short to earth on the SMD resistor pads so indicating that they would now be ok.
Afraid when testing although TV powers up OK there is no picture. Both Va and VS voltages are fine but Ysus derived voltages VSCH and VSC are up and down and unstable. When Noldud removed the buffer board these voltages stabilized indicating that the problem was with the buffer board. In my particular case it doesn't make any difference whether the buffer board is connected or not both VSCH and VSC voltages remain erratic. Just in case Ive tested the buffer board doing zip test and found all ok.
Have tried to source a second hand board fro usual sources but with no luck so have to continue with this repair.
Anybody any idea what might still cause VSCH and VSC voltages to remain unstable with voltages going up and down when the buffer board is not at fault??

[satinser]

Re: PS42B430P2W PS42B430 Blank screen nothing - VA and VS good

Any help appreciated