Sony FWD-42PV1 not switching on - Solved? require verification

[Grunder]

Hi Guys, this Sony plasma came in not switching on. Red led on, and no relay action. (refer to photos)

Whilst checking for Short circuits, I noticed R4 looked a bit cooked, and it measured open circuit.

Two components that connected to it were short circuit.
Q101 (P7NK70Z) I replaced from an old pcb.
Q16 (SUM45N25) I replaced with a new one.
R4 was a PROBLEM IDENTIFYING, I replaced with a 10 ohm?

Set has run for over two hrs, and still running.

Vs measures 185v (label says 184). not altered.
Va measures 44v (label says 45v) not altered.
-Vy measures -75v (label says -75v) not altered.

Now the " oh shit I'm stuck" part....

The manual says the Vsc should be measured on R53, and it should measure 120v.

DOES THE MANUAL MEAN MEASURE FROM GROUND TO R53 (270k)--120V, or
ACROSS R53.

ONE SIDE of R53 I GET -75V ( -VY), THE OTHER SIDE 44V. ACROSS R53 119V.

120v/ 119v, and the sets still running.

Please help me figure this out. I have read the AN1088 on how the Ysus operates, but this vsc has me baffled (actually plasmas on the whole.)

Thanks.

[ReeceyBurger123]

Re: Sony FWD-42PV1 not switching on - Solved? require verification

Is the image poor when its running then ? Also you might of missed something like a burnt gate drive resistor on one of the shorted fets.

[Grunder]

Re: Sony FWD-42PV1 not switching on - Solved? require verification

Is the image poor when its running then ? Also you might of missed something like a burnt gate drive resistor on one of the shorted fets.

Hi Reecey, The image looks fine. I had run the set for 20 mins on initial repair, and nothing seemed to get too hot either?

So I should be measuring between ground and R53? Not across.

When there is more than one component of the the same specs on a pcb, I usually compare readings to make sure that there aren't any drastic differences in measurement, which I'm sure I did with these 8 FET's.

Is it possible to say what would occur if I left the set running with the vsc low?

[Grunder]

Re: Sony FWD-42PV1 not switching on - Solved? require verification

Yes Reecey, on re-looking at the photo of the Fets, I see the the one gate drive resistor looks a bit blackened.

I had hoped the measurement was across the resistor R53. https://www.badcaps.net/forum/images...s/icon_sad.gif

Will have to re-check. Thanks. https://www.badcaps.net/forum/images...es/biggrin.gif

[flocko]

Re: Sony FWD-42PV1 not switching on - Solved? require verification

VSC is measured across resistor(R53) on these LG Y Sus boards and would be correct at 119-120v

[Grunder]

Re: Sony FWD-42PV1 not switching on - Solved? require verification

VSC is measured across resistor(R53) on these LG Y Sus boards and would be correct at 119-120v

phew! Thanks Flocko. Was putting off opening this set again. (lots of things to undo to get the Ysus out.

Really chuffed. Thanks a million!