CurtPalme.com Home Theater Forum

[mmastera]

I know it should be simple, but I'm as green as it gets with TVs...I'm a computer tech by trade and looking to maybe branch out even if just a hobby.

I have an LG 42PC3DD-UE (Insignia NS-PDP42) with no video. The unit powers up and I get audio, never shuts down or does anything else weird, just no video. I've checked both fuses on the power supply and both on the YSUS board, all are good.

Most info that I've found on the net suggest YSUS board but I don't want to be wrong if I can help it so I'm trying to narrow it down a bit more...I'm trying to test the Va and Vs on the power supply. If the TV has been on for a minute or two when I try to test for them, I don't get much: Vs - 3.7v, Va - 0.0v. Based on this I thought maybe it's a bad power supply...

If I have the DMM hooked up and then I turn the set on, I see Va and Vs indicate the expected values based on the sticker on the panel, then drop to the above values just about the time audio comes online. So now I know that the PSU is able to produce the correct voltages, I just don't know if I'm supposed to be seeing them once the set is fully powered on (I assume I should) but I'm only seeing them for a brief period while the set is booting up....

Am I testing for Va and Vs correctly? Should it be as simple as testing for them once the set it on and either seeing 60V/190V or not or is there a procedure to this that I'm missing?


On another note, can anyone recommend any books, resources on the net, etc... on the subject of learning flat panel TV repair?

thanks!

[macgyver655]

Disconnect the harness to the Y and Z SUS and see if your voltages return.

[mmastera]

Thanks for your reply. I've done a bit more checking...

Aside from the low-volt harnesses going to the tuner/main board , it appears to me that there is only one harness which goes to the YSUS, and the ZSUS is fed from it. Anyway, with the YSUS disconnected, same results...so I kept going and one by one removed the low volt hardnesses as well with no change. Finally, I have everything disconnected from the PSU (except for AC input)...when I plug the AC power cord in the relay clicks (apparently the PSU is "on" in the absence of the power switch being connected?). I still only see Va and Vs for a few seconds when power is applied then they die off. Not sure if this is important, but Vs (normally 190v) goes to 210V before abruptly dropping to 3.7v. Va goes to 60-61v as the label says it should before dropping to 0.0v.

I don't have the experience to know if I should be seeing Va and Vs at the labeled values at any given point during the operation of the TV but based on your reply I'm guessing I should and that the absence of the labeled values past the first few seconds of operation lends itself towards a bad PSU?

thanks again, I hope to keep learning and eventually add another "tool" to my belt...

[macgyver655]

I would start testing/replacing the caps in the power supply. Especially the 3300uf/10v ones. Up the voltage on these if you replace. Or order a new/rebuilt supply, but where is the fun in that?

[mmastera]

thanks again...

So sorry to beat a dead horse, but based on the progress of this thread I think that I understand that on a good PSU, I should be seeing the labeled Va and Vs from the PSU even when there's nothing else plugged into it besides AC power?

I may give the capacitors a shot, I am as green as it gets when it comes to this, but I have soldered before and this looks do-able. I'm trying to see if it's possible to test the caps with nothing more than a DMM (without a specific capacitance testing function) as that's all I have...

When you say to replace with a higher voltage, I'm assuming that the capacitance rating stays the same right? (ie get 3300uF 16V instead of 300uF 10V)

I may get a replacement PSU anyway and then take my time with the bad one using it as a learning tool...