Samsung Plasma PN50B450B1D Dim picture, black pixels

[tom66]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

The meter might be being fooled by some of the low pulses.

[Glitcher]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

So the x-main is bad? Would it also explain the low Yscan voltage?

[tom66]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

If you unplug X-main is Y-scan better?

[Glitcher]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

I unplugged the x-main from the psu and then from the ctrl board but Yscan would still is stay lower than the spec. Only time I can get Yscan to the specs is if I unplugged it from the ctrl board.

Also theres a green LED that's been blinking as the tv is on fromt he control board, not sure if it means anything.

[tom66]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

Lower than spec, by how much? Few volts OK. More than 20% lower bad.

[Glitcher]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

around -176-179v fluctuating

sticker says -193v

[tom66]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

Yeah that could be caused by a shorted Ve what happens with control+Y-main hooked up but X-main disconnected on both cables (white and grey power)? If Vscan is OK then it's probably a shorted intermittent Ve causing the fault on the X-main.

Just realised I remember doing the 42" B450 with bad X-main and same poor picture.

[Glitcher]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

I see, guess the only thing left would be a bad driver IC on the Xmain? I checked every through-hole FET and diode out of circuit and they were all good. I hate checking SMD parts =( not very much successful with those.

[tom66]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

If I see a driver IC I would always replace it at the same time as a FET, just because they are difficult to test.

[Glitcher]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

But then none of the FETs were bad, so not sure which I should replace or what I should be looking for

[tom66]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

I have to admit I just found a cheap X-main and swapped it, guess they're a lot harder to get hold of now as that was about 2 years ago...

[Glitcher]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

Ive been checking everything on this X-main and I can't seem to find one thing bad on it... there isn't as much components on the back of the board as I thought.

So far I just replaced the chip in the 2nd picture that leads to the ribbon to the control board but no luck.

Been checking especially around where the Ve test point is but no luck either...

[tom66]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

Vcc fuse is good?

[Glitcher]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

I assume you mean this one? And yes both fuses are good.

[tom66]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

Yes, that one. And do you get a good 15V or so going into that board?

[Glitcher]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

Yes, getting 15.48V on both ends of that fuse.

[Glitcher]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

Also a note, I'm measuring voltages on random parts on the X-main and (ie, the FEts, diodes, etc.) And they all are fluctuating and unsteady. Is this normal in an x-main

[tom66]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

I just checked the SS board of a Panasonic plasma and the output to the panel, despite being a square wave, measures 120V DC on a true RMS meter.

[Glitcher]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

Yeah that could be caused by a shorted Ve what happens with control+Y-main hooked up but X-main disconnected on both cables (white and grey power)? If Vscan is OK then it's probably a shorted intermittent Ve causing the fault on the X-main.

Just realised I remember doing the 42" B450 with bad X-main and same poor picture.

I just realized that I never answered this question. With the y-main board connected to psu and to the ctrl board. And the X-main disconnected (both connections) from the crtl board and the psu, the Vscan voltage is still low. It seems like it is independent from the x-main?

[tom66]

Re: Samsung Plasma PN50B450B1D Dim picture, black pixels

Depending on the design it could be that the -Vsc only rises when the Ve has sufficient load i.e. X-main working and panel lit fully. To test you could try hanging a 10W light bulb or xmas light off the Ve.