LG 50PC1DR repairing/diagnosing dark picture

[basros]

Hello
I just acquired from a friend of mine an LG50PC1DR that was headed to a landfill.After I plugged it in nothing lit up at all, so I took off the back and discovered many bulged caps on the power board so I replaced them all with new Nichicon's.

When I plugged it in I got the red standby and after turning it on the sound was there and all the other functions worked (ie:menu,input,ch-select ect). but the picture was very dark or washed out.

After looking at the manual I started to check voltages and found that VS,VA&5v inputs on the Zsus board were OK but that the developed voltages were Z Bias 150v instead of 90v and that the IPM of 18v was 0v

On the Ysus board VA,VS & 5v inputs were OK but the developed voltages were VSC negative 115v instead of a positive 115v and VY was 196v positive the IPM voltage of 18v I did not know where to measure it.

Is the Ysus board dependent on the Xsus or vise- versa or not at all

I could replace the IPM's for the Ysus board and buy a working Xsus board
because I think the set is worth fixing and not sending to the land fill

If anyone has any suggestions please let me know

Thanks
Basil

[Alastair E]

Re: LG 50PC1DR repairing/diagnosing dark picture

On these, A faulty Z-SUS IPM will give the symptom you describe.

However--The V-ZBias being that far out can cause weird effects too...

The IPM 18V is actually 15V --One side of the board is marked, 18v other 15V and as the regulator is a 7815 15V is the correct value. This supply is derived from the 5V rail by that DC/DC converter on the Y-SUS on the board just under the IPM heatsink--Not the two sub-boards that develop the other rails.
This DC/DC Converter derives Two 15V rails and another 5V rail. Some are floating supplies others ref to ground.

Y-SUS and Z-SUS work independantly--but their output is synchronised.

Be aware, The test-points for the VSC and the -VY are measured across components a cap and a resistor--cant remember which is which--board is marked as to which.
--VSC and -Vy are measured as I say--Across these parts and Not from them to chassis.

V-ZBias is from chassis to the tab of that MOSFET on Z-SUS....

[basros]

Re: LG 50PC1DR repairing/diagnosing dark picture

Thanks for responding
So do you think that my idea of replacing the two IPM's on the Ysus board will work
and should I replace the Zsus board as well
You see I don't know if the IPM's are the same on both boards or not
the ones I can get are Sanyo SPI50X3E120
are they all the same on both boards

[Alastair E]

Re: LG 50PC1DR repairing/diagnosing dark picture

The SUS IPM's will be different to the ERC IPM's

Both SUS IPM's and both ERC IPM's are the same, but different to each other....

As I recall, the IPM's are YPPD-J016C and YPPD-J017C....
Cant remember which is the ERC or SUS, and have NO idea the equivalent 'Sanyo' device....
--There's one of each on each board.....