LG 42LC7D-UK Repair

[obix]

I just put this model on my bench this week, a LG 42LC7D-UK. I replaced all the caps on the SMPS, and stuck a 6.8ohm/2W resistor in for R109, it was a thermo fuse/resistor. Now this unit is dark, not even red/green led on front... I'm going to mess with pulling the PWR_ON high with some batteries and pull and check all the MOSFET's on the power board next. I've got clean power through the second iso-transformer, and 165Vdc off of rectifier... There does not seem to be any power on any of the outgoing connectors.

I've gotten the service manuals for the -AB and -UB versions but can't seem to come up with the one for this -UK. What I really would like is the schematic and parts list for the power board if anyone knows where it could be had.

Any pointers would be greatly appreciated, thanks!

[Caleb]

Re: LG 42LC7D-UK Repair

Not sure if this is one you already have, its in deja vu format so you have to get another viewer to read it

[obix]

Re: LG 42LC7D-UK Repair

Thanks Caleb, yep actually I do have that one. It's for the -AB subversion and only has the partial schematic for the Main board which is different. However, I believe that the Power board is the same but they don't give the schematic for that... It's the LG EAY32731102 ( FSP286-6F02 ), this is a 2008 model.

[budm]

Re: LG 42LC7D-UK Repair

Is this the exact board you have?
http://www.shopjimmy.com/lg-eay32731...pply-unit.htm#
LG EAY32731102 (FSP286-6F02, 3BS0152315GP) Power Supply Unit.
No need to do any force on right now, you need to get the standby power supply working first.
The STBY power supply section has IC U501 for the SMPS IC whcih drives the power MOSFET Q501 which drives STBY power transformer T103.
Small caps C505, C507 are part of the startup running caps that you need to check the capacitance and the ESR.
You also try running the board by itself without other boards connected to it to see if you will get the STBY Voltage back.
D205 is the rectifier, C216, C217, L203, C218 sre the Pi filter for the 5Vs at connector P201 pin 3.
So verify for sure that you do not have 5VDC at that pin.

Pictures provided by shopjimmy.

[obix]

Re: LG 42LC7D-UK Repair

Thank you for the help budm. Yep this is the same one, I'm following those threads also thanks. I'll be heading back to the my bench soon and will focus on the standby and the other areas that you listed. I pulled and tested Q501 earlier, it's good, so I bet you are right on with IC U501.

Hopefully I will have some useful info to contribute to the forum very soon.

P.S. - The display had been coming on previously and was staying on until turned off, however after it was turned off it would not come back on...

Also, when in standby is the power led lit? I currently have no signs of life.

[budm]

Re: LG 42LC7D-UK Repair

We will need the P/N of that SMPS IC U501 so you can verify if it has enough VCC to startup the IC.

[obix]

Part# U501

I'm finally getting back on this LCD. I got a close-up of ic U501, it is a NCP1230D6, which is a 'Low−Standby Power HighPerformance PWMController'. Here is a link to the DATASHEET. I'll try getting some measurements then post them.

[budm]

Re: LG 42LC7D-UK Repair

OK, per spec sheet, the HV is applied to pin 8 which has the charge pump circuit to charge up the Capacitor on VCC pin 6, when the DCV reach 11.6VDC, the circuit will then start running which then the running Voltage for the IC will be generated by the AUX winding of the power transformer to keep itself running , the charge pump circuit at this point will be shut off.
You can see the application circuit on page 11 on how the IC is used.

[obix]

Re: LG 42LC7D-UK Repair

Here are the results using pin#4 as the GND:

Pin#6 = 8-10.3 Vdc
Pin#8 = 164 Vdc

Would you say that this means that startup voltage at pin#6 is too low? What happens if I give it a little boost to see if it will start?

[budm]

Re: LG 42LC7D-UK Repair

That can be that the electrolytic caps (C505, C507) connected to pin 6 may be bad (high ESR, low capacitance), or D205 I mention in post 4 may be leaky or shorted.
The circuit is on the HOT deadly side of the circuit so do not try to attach any external power supply to it.

[obix]

Re: LG 42LC7D-UK Repair

I pulled and checked caps with ESR:

C505 22uF / 50V = 0.41
C507 0.47uF / 50V = 3.7 ( strange this cap is larger then C505 but I'm sure there's a decimal on it )

Wish I had the schematic and parts list for this board... I'll check the diodes next.

[obix]

Re: LG 42LC7D-UK Repair

I pulled and tested D205 also, it seems fine. It's a STPS20H100CT.

So I guess the question right now is why isn't Pin#6 on U501 reaching the 11.6 Vdc?

I'll start on the other possibilities you mentioned in post#4 tomorrow, thank you so much for youCan't never could do nothin' r help on this one, it is very appreciated!

[obix]

Re: LG 42LC7D-UK Repair

Ok, C507 is bugging me. I just tested out of circuit on my DMM, which only goes up to 20uF, and it climbs above this, I swear it reads ".47uF" but it MUST be a "47uF". In which case it's definitely bad. So I'll replace this and see what happens.

[obix]

Re: LG 42LC7D-UK Repair

I replaced C507 with a 47uf/50V but still no change in the voltage levels on IC U501 Pin#6...

Also, there is no voltage at P201 / #3, actually I don't get a voltage reading on any of the pins on P201 thru P206.

[budm]

Re: LG 42LC7D-UK Repair

You may have bad IC that is not allowing pin 6 Voltage to reach the required start up Voltage, as you can see there is internal 20V Zener that may be leaky.
BTW, you running the power supply board by itself, right?

[obix]

Re: LG 42LC7D-UK Repair

Ok, I'll see if I can get a replacement U501 from Mouser or Digikey, I'll post back with results. Thanks again so much for the help!

[obix]

Replacement for U501

Do you think this one from Mouser would work as a replacement? LINK

It looks like the same think.

Also, when removing U501 I ruined the trace pad for Pin#1, It doesn't look like it connected to anything, the datasheet says it's a direct connect to Pin#6. With two magnifying glasses and three flashlights it appears as though Pins 1 & 7 are both N/C.

I'm wondering if this board is too hosed and I should look at a replacement SMPS board... I hate to let it beat me grrrr...

[vinceroger69]

Re: LG 42LC7D-UK Repair

Did you see budms edit in post 15?

[obix]

Re: LG 42LC7D-UK Repair

Thanks Vince, yes I had missed that edit. Yes, I am running the SMPS board with only the AC main connection. I'm ordering the above mentioned IC from Mouser, hope it comes soon.

[vinceroger69]

Re: LG 42LC7D-UK Repair

The part is cheap enough so certainly worth changing it.