LG 42PC1R Bad picture

[killer666]

Hello!

Does anybody know where is this tv -vy, vsc z-bias and other testpoints? I was tried to measure these but on d.m.m. screen shows random voltage. I think maybe i was measured wrong points?
On sticker va is 186v, when i turn potentiometer and set voltage minimum 177v before tv shuts down , then picture goes to normal. But onlu when on screen is darger image, when comes lighter then white areas is starting flicker.

If i set va to normal 186v, then all colors is messed and red tod and stripes and flickering is showing.

Sorry for bad language=D

[ReeceyBurger123]

Re: LG 42PC1R Bad picture

Ahh I fixed one off these recently, the fault is caused by the Zsus. The point of failure is the Ipm module under the heatsink. Replace the Zsus and the set should be good

[killer666]

Re: LG 42PC1R Bad picture

I tried to measure several times z-bias voltage on z-sus board, but every time i get same voltage as va 60V. Replaceing whole board is impossible, because its very rare tv set in here.

Can anybody tell how to test that Ipm module to be sure that is faulty?

[mmartell]

Re: LG 42PC1R Bad picture

Download the service manual from elektrotanya I think there is expected readings in it. However this is a common fault on these and they can fail "open" as well where the fuse remains good. You can source the ipm from a few places but keep in mind they are mostly pulls with unknown lifespan remaining.

[ReeceyBurger123]

Re: LG 42PC1R Bad picture

You can check if there are any pins like vs have any shorts to ground.

[mmartell]

Re: LG 42PC1R Bad picture

Is the zsus fuse blown ? Is so the ipm needs replacing and check any power resistors in its vicinity.

You were asking for the test points so how are you measuring Vbias ? I have a meter here that can read standard dc voltage but couldn't read anything with a floating ground. It's probably a longshot but thought I'd put it out there.

[killer666]

Re: LG 42PC1R Bad picture

All fuses are not blown, there is some little smd fuses, but they was ok.

I tried to measure z-bias, -vy and vscan, but no result. If you say these are floating ground then i need different voltmeter?

Here is one more symptom ; when i turn z-bias potentiometer, then no changes on screen.
Imeasured between ground and z-bias + testpoint and reading is same as va 60V.

[mmartell]

Re: LG 42PC1R Bad picture

I can't say definitively but I suspect the z sustain ipm has failed open and needs to be replaced.

[ReeceyBurger123]

Re: LG 42PC1R Bad picture

I have seen an ipm fail and not take the fuse it is possible.

[killer666]

Re: LG 42PC1R Bad picture

How i find that ipm model nr or replacement part model nr?

[ReeceyBurger123]

Re: LG 42PC1R Bad picture

You will need to either desolder the old ipm and find its part number which is what I recommend or you can look up the board number and see if any ipms are listed for it.

[killer666]

Re: LG 42PC1R Bad picture

I found fault on z-sus board. On z-bias voltage control board i was replaced kia431a, and then on z-bias testpoints shows 75V. Then i turn potentiometer and its goes to 100V.

Now i found one new symptom, when i tried to raise vs to normal voltage then Z-bias testpoints shows random voltage. Like vsc and -vy

Z-bias , -vy and vsc voltage control boards is all same type. Can you explane me how i can measure z-bias, but i cant measure -vy and vsc?
I now tried to measure them directly pins on voltage control boards, but same randomly changeing reading appears.

I think there is some fault on power board?

After seting z-bias to 100V then picture is allmoust perfect, but randomly white areas is flickering...

[mmartell]

Re: LG 42PC1R Bad picture

I think you have a problem with your DMM. What brand is it ?

[mmartell]

Re: LG 42PC1R Bad picture

Ok just looked at your pic. -Vy is measured across the resistor. Vsc looks to be tied to at least one leg of the cap. Look around the board for another "Vsc" marking - it could be the other test point. Otherwise I would say the correct reading would be taken across the cap.

Or you could do like I suggested earlier and download the service manual as it likely has the test points laid out.

[killer666]

Re: LG 42PC1R Bad picture

I have downlaoaded service manual, but there is not mentioned where testpoints are. Only for va and vs testpoints. I have cheap noname dmm . I try another one tomorow.