LG LCD power supply

[vinceroger69]

Re: LG LCD power supply

just tested these resistors too all measure ok and the same on both boards

It first goes through a resistive divider formed by SMD resistors R202 and R203.
Then there is some logic signal going on with SMD transistors Q200 and Q201 and SMD resistors R200 and R201.

[vinceroger69]

Re: LG LCD power supply

just going too test these for you now R219 and R205

[vinceroger69]

Re: LG LCD power supply

R219 1081 measures 1.800 on 2k
R205 1001 measures 1.00 on 2k

these readings are the same on both boards

[budm]

Re: LG LCD power supply

just going too test these for you now R219 and R205

Check to see if you're also getting 1.2V on the feedback.
BTW, did you replace the filter cap for the output of this 3.3V circuit?

[vinceroger69]

Re: LG LCD power supply

all capacitors replaced with panasonics budm will measure voltage now

[vinceroger69]

Re: LG LCD power supply

0.78 v on fb pin on bad board
0.85 v on fb good board

[vinceroger69]

Re: LG LCD power supply

just to clarify this
Now, what is puzzling is that first P201 test, where you got 2.05 Volts both for the good and bad boards. Was the TV still working? If the voltages are the same, I don't see why the "bad" board would have caused problems then. Seems the results would be inconsistent... unless you measured or wrote down those test voltages incorrectly. (But I doubt that)

p201 is the 3.4 on pin on the connector 2.05 volts on both boards (i guess this turns the 3.4 section on thats on p202/p203 connector 2.21 on bad board tv wont work 2.87 good board tv works.

[vinceroger69]

Re: LG LCD power supply

im seriously thinking of using a ebay dc to dc convertor yes there cheap also can add a heat sink etc now the bad bit is on the tv psu board its printed the 3.4v rail needs 5amp is this correct?

would this work?
http://www.ebay.co.uk/itm/4-38V-to-1...AAAOSwEetV-6~x

[budm]

Re: LG LCD power supply

That should be more than enough, I believe Tom66 did do some mod like that but I am not sure, I am not sure if this power supply has to be off and be turned on at the right sequence by the main board or not.

[vinceroger69]

Re: LG LCD power supply

im not sure budm to be honest can i link the 3.4 v on wire to the other 3.4 volt ones going back to the main board? (i will of course remove these wires from the connector at the psu end then re connect too the new 3.4v board i have plenty of room to mount it.) Thanks again budm and momaka for your input in trying too fix the old section of the psu im sure both of you could of fixed this if you had the board in front of you and if you was in the uk i would of sent it too you if you wanted too try but hey i will class my fix with this additional board as a mod and not a bodge job.

[budm]

Re: LG LCD power supply

I think if we can get the IC spec of that EBAY board, we may be able to turn it on and off.

[vinceroger69]

Re: LG LCD power supply

Ok once it arrives i will update this thread thanks again.

[budm]

Re: LG LCD power supply

I may get one of that power supply myself, good for powering up the circuit that has failed power supply section.

[vinceroger69]

Re: LG LCD power supply

I have ordered two myself at that price cant go wrong pity it does not say if it comes with the heat sinks as shown in the pictures i will find out in a few weeks i guess.

budm to power this replacement board where would you get the supply voltage from i was thinking of the 24 volt line as that runs at 6 amps and then use the convertor to drop the voltage down etc or would you recomend using another voltage line.

[budm]

Re: LG LCD power supply

It looks like it can be fed by the 5VSTBY just like the original circuit, the load current will still be same as before, the limit will be up to what the load will draw, the load for that new 3.3V supply is not going to be any more than what the old circuit can provide.
According to the spec, the board can take in as low as 4V, and the out put can be adjust from 1.25V and up, so it should have no problem converting the 5V into 3.3V output.
You should remove the two MOSFETs and the U200 from the board.
I would connect the input pin to the old 5VSTBY inductor output pin that feeds the old circuit, and the output pin of the new supply should be connected to the output filter inductor of the old circuit.

[vinceroger69]

Re: LG LCD power supply

Ok budm will do that thanks again.

[vinceroger69]

Re: LG LCD power supply

like this budm once removed the three parts

[vinceroger69]

Re: LG LCD power supply

I may get one of that power supply myself, good for powering up the circuit that has failed power supply section.

budm these have just arrived today and they do with with the heat sinks that stick on too the ic i will remove the smd parts you mentioned from the old psu later and set the output voltage up and find somewhere to mount the new module.

[momaka]

Re: LG LCD power supply

i will remove the smd parts you mentioned from the old psu later and set the output voltage up and find somewhere to mount the new module.

Actually, before you do that, I think we may need some of them to implement the control of 3.4V when 3.4V_ON is high. I will try to draw a diagram/circuit for you a little later today.

*OR* if you want to go ahead and try plugging in the buck converter anyways without using the 3.4V_ON control, that's fine too. Just make sure to save the SMD parts you remove in case we do need them.

[budm]

Re: LG LCD power supply

We need to find the spec sheet of that IC used on the board you just bought to find out if there is any ENABLE pin so we can use the 3.4V_ON signal to control it.