need help troubleshooting lg plasma

[FrenchConnection67]

Hi everyone,

I would appreciate some help for troubleshooting my plasma lg 42gt45.

Please see what i ve tested so far below:

Fault symptoms: power supply shuts down instantly after turning on the tv.

Tests:

1. Checked my psu output with everything connected none

2. Disconnected the z sus and tried, fault remains the same

3. Disconnected the y sus and tried, tv turns on, main board lights turns on, vs and va outputs are good for about 10-15s and then goes dead but tv stays on. Now i am wondering whther it is not normal for the vs and va to go dead after the logic board not getting any feedback from the x and z sus board ??????

3. Funny enough, when i unplugg the ribbon between logic and y sus, i can reconnect the y sus to the psu with just the z sus disconne ted and the tv turn ons

I am now a bit confused but my primary doubts are on the y suz board

What do you think?

[tom66]

Re: need help troubleshooting lg plasma

Are you sure about that model number?
On some LG plasmas, the Vs and Va are shut down a few seconds after the sustain boards do not output a "go" signal.

[FrenchConnection67]

Re: need help troubleshooting lg plasma

Hi tom, the model nunber is 42pt85 sorry my mistake.

[tom66]

Re: need help troubleshooting lg plasma

Using an ohmmeter, test across the Vs on the Y-sustain. Power MUST be unplugged from the Y-sustain board! Hold the reading until it appears to stabilise.

[FrenchConnection67]

Re: need help troubleshooting lg plasma

i ve just measured between the two vs pins on y sustain board and it reads 0.02 ohm.

[tom66]

Re: need help troubleshooting lg plasma

That would indicate the Y-sustain has a dead short on it.

The most common fault is the IPM pack on it. However this is extremely difficult to replace unless you have a very good soldering iron and the skill to use it. (Min about 70W.)

An alternative is to replace the Y-sustain or get it repaired. Cheapest I see for a new board is £54
http://www.ebay.co.uk/sch/i.html?_tr...at=0&_from=R40

I can't see any repair services but the repair is identical to the 42X2/X3 panels which have a lot of Y-sustain failures. (The 42X4A IPMs rarely fail.)

[FrenchConnection67]

Re: need help troubleshooting lg plasma

yeah i ve also seen that y sustain board for 54 pounds. a bit expensive like, but i ve also seen a a ipm repair kit for 24 pounds which might be the solution. i have three different soldering irons but not that powerful, i have soldering gun though and this is very powerful however not that precise due to its big tip. i ll find a way anyway.

but you know i ve also measured between the two vs on the psu and got the same value 0.02 ohms (disconnected from the y sus), is that normal?

[tom66]

Re: need help troubleshooting lg plasma

For the PSU you will need to hold the reading for some time and wait for it to settle.

[FrenchConnection67]

Re: need help troubleshooting lg plasma

i ve hold my measures for at least 1 minute and it reads 0.2 ohms same as on the y sus board (said 0.02 before but misspelled it).

[tom66]

Re: need help troubleshooting lg plasma

Is the same present on the power board?

[FrenchConnection67]

Re: need help troubleshooting lg plasma

yes i read 0.2 ohms across the two vs pins on both boards being not connected toguether. why? what kind of reading should we roughly get? are they not connected toguether as they supply the same voltage?

[tom66]

Re: need help troubleshooting lg plasma

Ugh, sorry. I misread you, I thought you meant Vs and GND. That is fine, yes all the Vs are connected together. (This is true on virtually every plasma TV.)

[FrenchConnection67]

Re: need help troubleshooting lg plasma

so i ve measured again but now from gnd and vs and get a normal reading, no continuity (on both boards)

any other test i could do to isolate whether it is really the y main and not the x main causing the problem. Because how do you explain that when i disconnect the ribbon cable between the logic board and the y main, the tv turns on with the y main connected but not with the x main?

but when the ribbon is connected, none of the board are allowing the tv to turn on?????? confused there

[FrenchConnection67]

Re: need help troubleshooting lg plasma

anyone else? any ideas guys