Sharp lc-60le810un power supply

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Hello. I have a dead TV with at least a power supply problem. I have 5v standby, but when I force the power supply on, I don't get all the output voltages. In particular, I get 0v on the 12v PL connector or PNL-PWR signal. The PFC boost is not working--voltage on the main caps stays around 160v.

I don't know much about how to troubleshoot the PFC IC and related components. As shown better in the third photo, R7903 reads 0.7ohms in-circuit, so I am thinking it's shorted. I am not sure what the resistor value is supposed to be because it's located under a heatsink for Q7901 and I can't see it. It appears to be connected to the gate of Q7901, which itself doesn't seem shorted. No idea about IC7901. Is it likely only the resistor is bad? Thanks for taking a look--I appreciate the help.

[budm]

Re: Sharp lc-60le810un power supply

R7903 should be <1 Ohms, that is the resistor for the Source pin of POWER MOSFET Q7901.
How did you go about forcing on the power power supply? Which two pins did you use?
PNL-PWR is the command receiving pin which needs >2.5VDC to force on the SWITCHED 12V LDO for the output 12V-PNL pin.
I need much better pictures of the whole top side and the bottom side, and then the closed up pictures of the connectors that clearly show the pin names of each pin.
I cannot read the model number of the board as printed on the barcode sticker, I can see DPS-????????

[crosstalk]

Re: Sharp lc-60le810un power supply

To switch it on, I was connecting BU5V to PS-ON. When I did this, the 13.2v lines turned on, but the main caps didn't boost to 400v. What do I do with PNL-POW? Short that to 5v?

Hopefully the new photos are better. There are several posts here about LED strip problems with this model, so that could be the real problem here. But the set appears dead so far, so maybe the power supply is the problem. The barcode reads "DPS-219EP A"

[budm]

Re: Sharp lc-60le810un power supply

"What do I do with PNL-POW? Short that to 5v" You use 330~1K 1/4W resistor between BU5V and PNL-POW to turn on the switched LDO IC Q7909.
I ALWAYS use resistors for forcing on the circuits. So you need to have PS-ON and PNL-POW force on signals to get the 12V at the PL connector.
But you still have problem with the PFC Voltage booster, you need to check Diodes D7805, 7806, and 7808.
Need to also check and see if the PFC Controller IC is getting the VCC to run. Can you get the P.N as printed on top of the IC?
The LED driver circuit needs that boosted Voltage to run.

DELTA 'DPS-219EP A' Pictures provided by SHOPJIMMY.

[crosstalk]

Re: Sharp lc-60le810un power supply

Using a resistor, I was able to force ps-on and pnl-pwr and got the 12v output at the PL connector.

I checked diodes D7805, D7806, and D7808--they seem fine with diode test mode on my multimeter (.4v drop one way, OL the other).

Still getting 156v on the main caps. The PFC controller IC is 3BS3LJ. Pin 7 (which I think is Vcc) is -21vdc with black multimeter lead on the ground screw of board and red lead on pin 7. Seems like this should be +21v.

D7910, which is connected to pin 7, seems strange to me. It has 0.5v drop with leads one way and 0.6v drop with leads the other way. The part seems to be marked "5D" but it's difficult to read.

[budm]

Re: Sharp lc-60le810un power supply

"Still getting 156v on the main caps. The PFC controller IC is 3BS3LJ. Pin 7 (which I think is Vcc) is -21vdc with black multimeter lead on the ground screw of board and red lead on pin 7. Seems like this should be +21v."
You are working the Primary side DC circuit so you need to use the negative leg of the Main filter cap (All 3 caps are connected in parallel so you can use any one of the Negative leg) as the GND ref for your meter.
You also got the wrong IC, 3BS3LJ (ICE3BS03LJG) https://cdn.badcaps-static.com/pdfs/...cafb9b334d.pdf is the SMPS IC, IC7901.
The PFC Controller IC is IC7801.

[crosstalk]

Re: Sharp lc-60le810un power supply

Thank you. Now 16.21v at pin 7. Bad IC?

[budm]

Re: Sharp lc-60le810un power supply

Please see post 6, you look at the wrong IC.

[crosstalk]

Re: Sharp lc-60le810un power supply

Sorry--I obviously missed that part of the post. IC7801 is 1608B. VCC (Pin 8) has 0v. I attempted to attach the correct datasheet.

[budm]

Re: Sharp lc-60le810un power supply

OK, good to have the pinout.
The VCC to run this IC is generated by the AUX winding of the standby power supply transformer. This VCC from this AUX winding will be fed to switched transistor to supply the VCC to the PFC IC, this transistor is turned on by the PS-ON signal.
So at this point I/WE will have to trace out the connection form the standby power supply section to see how the VCC is routed to the IC.
You also should check the resistance between VCC and GND pin to see if it shows low resistance reading.

[crosstalk]

Re: Sharp lc-60le810un power supply

Resistance between VCC and GND is 11.9k. IC7601 (DDA002C) also seems to have 0v on its VCC.

Which one is the standby transformer? I will try to trace it out.

[budm]

Re: Sharp lc-60le810un power supply

T7901 is standby transfromer, winding on pin 1 (GND) and 2 is AUX winding for running the STBY SMPS IC, the D7913 and cap C7912 (all these are OK otherwise you will not have STBY power supply) is for making the DCV to run the ICs. It is the switched transistor and the resistor that I suspect to be bad or the switched transistor did not get the PS-ON.
Check the DCV and the resistor, See if I am correct.
Picture provided by SHOPJIMMY.

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Re: Sharp lc-60le810un power supply

The voltage between those points (DCV) is still 0v. The resistor looks a bit funky under the magnifier, but it reads about 10 ohms. The transistor Q7908 has 0.2v at the gate, 0v at the source and 16.85v at the drain. I guess the transistor isn't being switched on with just 0.2v. Where do I look next? Do you think the optocoupler (pc123) failed?

[tom66]

Re: Sharp lc-60le810un power supply

Can you determine the part number of Q7908? If it is a P-channel FET or PNP device, a low gate voltage is OK, but zero source voltage would not (it should be ON.)

[budm]

Re: Sharp lc-60le810un power supply

That may be just an NPN Transistor, just do the junction test between E-B, and B-C.

[crosstalk]

Re: Sharp lc-60le810un power supply

It is marked "W2X". Could be a PMBT4401 NPN transistor? E-B and B-C test like normal diodes (.6v with lead one way and OL with leads the other).

[budm]

Re: Sharp lc-60le810un power supply

So you not getting 0.6VDC between the E-B, then you need to see where the Base is connected to.
During this test you do have the force on signal feeding the PS-ON pin, right?
I can see that the Base goes to the opto PC7901??, so on the two pin of the LED side of the opto should have around 1.7~2V.
We are getting close.

[crosstalk]

Re: Sharp lc-60le810un power supply

Yes, I believe I have the ps-on forced to ~5v. The two pins on the secondary side of the opto are 4.5vdc on one of the pins and 5.5vdc on the other (with respect to the ground screw). Am I supposed to be measuring one pin with respect to the other pin?

[budm]

Re: Sharp lc-60le810un power supply

The LED side of the opto you will measure between the two pins of the opto.

[crosstalk]

Re: Sharp lc-60le810un power supply

I had a setback. I was probing between the two pins of PC7901 and found 1.02v, but then the probes slipped and I think shorted the two pins of the opto on the secondary side. They now have 0v between them. I also lost the standby 5v. Q7908 which had 16.85v at the collector now fluctuates 11-16v.

I am not even sure which opto I was supposed to be measuring. From top to bottom they are labelled pc7701, pc7702, pc7901, pc7703.