LG LCD power supply

[vinceroger69]

Re: LG LCD power supply

xlsemi
xl4015e1
52845

i have already removed the smds but can re add them if needed

[budm]

Re: LG LCD power supply

The ON/OFF implementation can be done on the FB pin per app notes page 8.

[vinceroger69]

Re: LG LCD power supply

so budm remember im new too electronics and still learing so what do i need to physically do too make this module work the supply in and output voltages im fine with its just this 3.4v on pin in need clarification on many thanks again budm

[budm]

Re: LG LCD power supply

At this point i would just try to see if we will get the 3.3V output from your new board first when the 5VSTBY and GND is fed to the board, no output of this board to the LG power supply board at this point but you should have 10 Ohms 2W minimum resistor for the load then adjust the output to 3.3V to make sure the new board is OK.

[vinceroger69]

Re: LG LCD power supply

ok i will check what large wattage resistors i have here and get back to you asap with results this maybe tomorrow evening now though as i have to pop out.

edit i have here 1x 10w 4.7 ohm cement resistoro or x2 5watt 4.7ohm cement resitors or a 2 watt 47 ohm resitor which is best for a test?

[budm]

Re: LG LCD power supply

" x2 5watt 4.7ohm cement resistors" will be find, just connect them in series first.

[vinceroger69]

Re: LG LCD power supply

thanks budm will post results tomorrow now.

[vinceroger69]

Re: LG LCD power supply

A update i managed to find room and mounted the power module, i loaded the psu with the resitors and set it to 3.4 volts, i then soldered the output to the 3.4 volt coil as per budms advice the good news the set now scans channels fine and has sound so im soak testing the set now. I did not do nothing to the 3.4on pin as the set seems to function ok as it is.

[budm]

Re: LG LCD power supply

Good news, so you removed the IC U200 and the two MOSFETs? I think they have the 3.4V_ON/OFF signal to turn off the 3.3V to reduce the power consumption when TV is OFF so the 5VSTBY will have minimum load.
Does the IC get very hot?

[vinceroger69]

Re: LG LCD power supply

too be honest budm didnt check the ic heat although i did fit the heat sink supplied too it i did check the running voltage of the 3.4v pins it read a steady 3.4 so under load the module did its job ok the 3.4 on pin still read 2.04 volts like it has allthrough my fault finding and swopping parts etc. I found a spare screw hole on the mainboard so attached the module too that and ran wires to the psu pictures included, the set seems to run fine but theres a lot of heat out the top vents and also the lcd has one dead pixel only visble on a black image.(yes removed mosfets and ic as your advise) thanks for your input guys another set saved from the landfill for a while at least.

[budm]

Re: LG LCD power supply

Glad to hear the TV is working, I may get some of that module to play with.

[vinceroger69]

Re: LG LCD power supply

They seem good for the money took a good few turns of the screw untill the voltage started to drop but seems to do the job ok and stuff at the minute coming from china too the uk takes around 9 days so not bad.

[momaka]

Re: LG LCD power supply

A update i managed to find room and mounted the power module, i loaded the psu with the resitors and set it to 3.4 volts, i then soldered the output to the 3.4 volt coil as per budms advice the good news the set now scans channels fine and has sound so im soak testing the set now. I did not do nothing to the 3.4on pin as the set seems to function ok as it is.

Nice!
Great to hear the set is running as it should be. I guess the original power supply buck converter does have a design flaw somewhere.

As for not using the 3.4V_ON pin... your TV will probably waste a little more power in standby, since the 3.4V rail won't be turned off then. But I guess that probably won't be too much of a deal for most people.

[vinceroger69]

Re: LG LCD power supply

Thanks momaka i know its not a proper fix adding the additional module but i carried out the fault finding as far as i could myself without a scope etc (yes i do have a 20 mhz one i need too test and see if it works correctly then i can try too learn how to use one) but for now this set is working if i had realised it had a dead pixel i probably wouldnt have bothered as its such a old set, but too be honest i have it on soak test myself still and i hardly notice it at all.This isnt my set a neighbour got it from out of our comunal rubbish bin room and asked me could it be fixed for them, i will show it them working tomorrow and show them the dead pixel and see what they want too do with the set, money wise it owes me about £10.00 in parts so not a bad result even if they dont want the set i may get more parting it out (except power supply/lcd) i will see what they want too do.

[Shannock9]

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 the voltage it receives.


So what happened when you put 3.4 v into the mainboard pin marked 1.1v? Did in mind that at all?

[Shannock9]

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.

[vinceroger69]

Re: LG LCD power supply

the tv on pin marked 3.4v seems to be quite common issue reading low just above 2 v theres a few threads on the internet regarding this .

[Shannock9]

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 was necessary to bring the TV from standby to running. But once that was done (and the mainboard was clamping the "3.3" at 1.29) the ATX could be turned off and the TV continued running (with the "3.3" still showing 1.29).

I've ordered a (used) replacement mainboard for further experimentation / elimination. This may seem economically suboptimal, but for me this is a hobby and a voyage of discovery. Also I prefer this TV to newer models as it has lots of non HDMI inputs and a really dark black with low reflection.

@vinceroger69 - what output voltage did you achieve with your DC-DC converter mod when connected to the mainboard?

[vinceroger69]

Re: LG LCD power supply

i still have this tv available i can probably take one more lot of voltage readings with the set in standby and in the working condition i think when my set was playing up i could not re tune any channels with the low voltage but once fitted the additional board all was fine.

which pin again is being pulled down on your set when its on?

[Shannock9]

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. 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.
====================================

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 wire. I would appreciate knowing what you have for both TV on, and TV in standby.

For the avoidance of doubt the "3.4 ON" pin is the last pin on another connector (BLUE arrow). That signal is also of interest please but not to be confused with "3.4v" (RED Arrow) which is my main concern.

For the negative wire on the meter you could use the heat sink marked GROUND in the photo, but be d*mned sure you get the right heat sink - the ones at the other end (nearer the mains input) are very "hot". Alternatively you could use the pin at the other end of the same connector (GREEN arrow).

BTW under the red arrow on my PSU I have removed L204 but yours may still be in place? Actually a photo or two of your fix/mod would be very nice.

Thanks again, Duncan