Re: LG LCD power supply

Thank you very much for responding, and a happy new year. I belatedly read your PM and that seems conclusive that I have a bad main board. I have a replacement on order so we will see. [B]Below is what I was going to ask, but I now understand you already successfully got the red arrowed point to read 3.4v with the TV on.[/B]
====================================

[COLOR="DarkGreen"]The "3.4v" pin is marked with a RED arrow in the attached photo. It's the first pin in the connector and on my TV is distinguished by a blue...

Re: LG LCD power supply

The TV heard us talking about it and has failed with "no signal". I recapped the PSU and no improvement - voltages unchanged. But I noticed that Q204 (= fsd6690Z, the upper half of the ST5v to 3.4v divider) was pretty cooked so I removed L201 and fed the TV 3.3v volts from an ATX PSU. This got vision but no sound, and the 3.3 was still pulled down to 1.29 (measured right at the ATX) by the main board.

Because the ATX and the original PSU needed to be switched on separately I also noticed the following - the substitute 3.3 from the ATX...

Re: LG LCD power supply

PLEASE IGNORE MY PREVIOUS POST #175 ABOVE. "My eyes are dim I cannot see." The main board is actually marked P_3.3v in scrunched up writing easy to read as 1.1v. Sorry for my confusion and any caused here.

Given my readings which I confirm, it does look as though my PSU is very marginal and waiting to fail like VinceReese69's. I will recap it at once.

Re: LG LCD power supply

If anyone is still interested in the so called 3.4v output, I have a working 32LC2DB and measured it. With the PSU running alone (disconnected from other boards) it measured 3.30v. But with everything connected and the TV running it was only 1.29 (and the 3.4v on pin was 2.03). With the TV in standby it was 1.16v (and the 3.4v on was 0.04). Interestingly at the other end of the 3.4v wire the main board is marked 1.1v !! so that is obviously deliberate. My guess is that the 3.4v on is an analog feedback (pull down for less volts) from the main board to control...

Re: New Members - please post your introductions here

Good morning All,
I got my first soldering iron in 1953 at aged 7, and was fixing valve (tube) TV's by age 12. Continued as a very serious hobbyist thru discrete transistors and then IC's, and picked up an EE degree along the way. But got distracted by programming and became a professional SW designer - worked on product prototypes and enjoyed arguing with the HW designers LOL. Now I'm retired and dusting off my practical electronic skills again. Current target is several SMPS in TVs and PVRs - I've ordered an in circuit...