Zenith P42W46X - Flashing Dim Picture

[drpj23]

This tv originally had the above stated symptoms and a little noise in the screen. The "No Signal" Text box would move around dimly lit but as if it was trying to go back to its original brightness.
The X-SUS had a blown fuse (C5: 250v 47uF). I had replaced that but no change to symptoms; the IPM was making a loud hum.

I ordered a new (well used) X-SUS and the noise and hum stopped but the image was still dim and flashing. If you were to leave it on for about 5 minutes the picture would actually go back to normal but if you pulled up the menu it went back and you had to wait for it to get back to normal. Small OSD like volume seem to not make it revert. The static on cable seem to be normal too (not dim).

So big question is, faulty X-SUS (again) or external factor?

Voltages are in spec and there are no cold solder joints that I could find.

X-SUS: 6871QZH033A
Panel: PDP42V6(0001)

[tom66]

Re: Zenith P42W46X - Flashing Dim Picture

When you bring up the menu do the voltages drop out?
It sure sounds like a faulty IPM/X-sus. (BTW, X-sus is a combination of LG and Samsung terminology... LG uses Z-sustain, Samsung uses X-main.)

[drpj23]

Re: Zenith P42W46X - Flashing Dim Picture

Heh, ya I do that sometimes :P

But on the bottom connecter there is a 15v rail that is at 12 when the image is OK but drops to 9 when I hit the menu.

There is a blue pot above that connector but I think that is for the ramp up - don't know

[tom66]

Re: Zenith P42W46X - Flashing Dim Picture

Careful with running with low 15V... has been known to cook the IPMs.
The 15V is supplied by Ysus using a separate power supply, check this; could have a bad cap.

[drpj23]

Re: Zenith P42W46X - Flashing Dim Picture

Didn't know that - suppose that was the original fault then.

I'll take it home tonight and check the caps on the board - nothing obvious right now.

[tom66]

Re: Zenith P42W46X - Flashing Dim Picture

The low voltage causes the IPM to be less efficient in turning on the transistors. Which can kill the IPM. So don't run it for too long with the low +15V; I'd say 30 seconds at most.

[drpj23]

Re: Zenith P42W46X - Flashing Dim Picture

There was a 47uF cap with 2.6 ohms of ESR but that wasn't directly tied to the 15v line.

There are some surface mount aluminum caps I will check tomorrow morning.

[drpj23]

Re: Zenith P42W46X - Flashing Dim Picture

Time was a problem, so I had to order the Y-sustain. Did fix the 15v rail but as most LGs, plagued with the green sparklies. Suppose firmware would need upgrading due to the new (different) sustain boards that were put in.