Vizio p50hdm dim screen

[freakaftr8]

Hey all. Well this tv landed in my lap and I am stumped to say the least. Love to hear some input on this as I have devoted two days into it so far. Sus out ipm popped. Replaced and for good measure replaced er ipm as well. Now I have a picture back but dim. Not a zsus issue as I have another exact set with a tested working zsus. This is not a blotchy dim mal discharge dim but just dim like the contrast level is cranked all the way down. I tested the board in the other tv with same results. Now what's interesting is that the ramp up circuit had a shorted r73. Replaced and still dim. Also found b47 b48 b28 b39 open. Replaced all and still dim. R7 and r8 r75 r79 all ok. All voltages on the board appear to be proper. I don't have a schematic on the board but have a good one I'm testing readings against. Cannot find the issue. Anyone had this problem after replacing the faulty ipm's? It's for sure in the ysus as a good one works fine in this tv and gives the screen a bright raster. The board is the dreaded 6871qyh039a

[freakaftr8]

Re: Vizio p50hdm dim screen

If its any help the sus out ipm is warm but not as warm as I think it should be as the er ipm is a but warmer. Zsus ipm's are obviously working as they are both decently warm and the same temp as each other.

[freakaftr8]

Re: Vizio p50hdm dim screen

I'm now under the assumption that the ysus sus out ipm is not under full power. Leaving a very dim but uniform screen.

Any input on this board would be greatly appreciated.

[tom66]

Re: Vizio p50hdm dim screen

The IPM cannot fail "half power". Only the Z-sus IPM or bad priming on Y-sus can cause dim image.

[freakaftr8]

Re: Vizio p50hdm dim screen

Ah yes the priming. Don't mean to sound dumb as I am very fluent in
Power supplies but on this board the priming is done by which circuit? Is it -vy?

[tom66]

Re: Vizio p50hdm dim screen

-Vy and Vsc, plus a few transistors, optocouplers, capacitors etc.
Negative period is important for erase and stability (sparklies.)
Positive period is important for brightness, black level and stability.

[freakaftr8]

Re: Vizio p50hdm dim screen

Ok so I have a grey panel on prime. It does have a so called prime upon startup. But the to e is very dim. Kind of like when you disconnect the zsus but not the blotchy picture you would see. The zsus is working at capacity. The ysus seems to be outputting proper -vy and vscan voltages as well. Although the modules are not getting as warm as I am used to.
Note that there was a failure of a resistor off the -vy poteometer and it was replaced as well as the "inductive links"? On the diodes under the sus out ipm. All restored and no change. This ones a head scratcher. I should probably have a look at the optos on the circuit but the voltages are there and does respond to adjustments.

[tom66]

Re: Vizio p50hdm dim screen

You may need to borrow a scope to test it. Also check Vzbias on Z-sus.

[freakaftr8]

Re: Vizio p50hdm dim screen

Z board is fine. Just tried again by swapping this y board into a working tv and same result. I am seeing different readings on the ic20 regulator for the input side of the sus ipm

[freakaftr8]

Re: Vizio p50hdm dim screen

Anyone ever had other problems with this board after an ipm replacement? It's obviously not priming the panel right although the output voltages seem ok with -vy at -200 and vsc at 115

[tom66]

Re: Vizio p50hdm dim screen

Vsc sounds a little low? Should be around 180~190V for these panels.

[freakaftr8]

Re: Vizio p50hdm dim screen

Really? The panel sticker is extremely vague

[tom66]

Re: Vizio p50hdm dim screen

115V is Vzbias.

What panel does this TV have? LG PDP50X3, LG PDP50X4?

[freakaftr8]

Re: Vizio p50hdm dim screen

What's the proper way to check vscan voltage on this board?

[freakaftr8]

Re: Vizio p50hdm dim screen

Is a pdp50x3

115V is Vzbias.

What panel does this TV have? LG PDP50X3, LG PDP50X4?

[tom66]

Re: Vizio p50hdm dim screen

See for alignments:
http://www.tgohome.com/ServiceManual...&Search=Submit

[freakaftr8]

Re: Vizio p50hdm dim screen

Well sure enough I get from -63 to max -145v on vsc test points and the +VSC pot on ps102 pack is where I am adjusting for the voltage adjustments. Not getting to -189v..

[tom66]

Re: Vizio p50hdm dim screen

I'm fairly sure Vsc should be positive. There could be a bad cap on Vsc output.

[freakaftr8]

Re: Vizio p50hdm dim screen

Is the adjustment +VSC the vscan adjustment. If it is and what I have found on the sticker in the panel +VSC is 115v. Is this vscan?

[tom66]

Re: Vizio p50hdm dim screen

The panel guide I linked to should make it clear, but for an X3-series plasma panel 115V seems too low to me.