Sharp lc-60le810un power supply

[budm]

Re: Sharp lc-60le810un power supply

PC7901, that is what I see the Base of the transistor is connected to.
The OPTO has the LED side and the Photo-Transistor on the receiving side.

[crosstalk]

Re: Sharp lc-60le810un power supply

So was the opto bad because there was only 1.02v between the pins? I obviously have other problems at the moment too.

[budm]

Re: Sharp lc-60le810un power supply

I expect more than 1.02V on the LED side. You can look up the spec sheet to see what it should be.

[crosstalk]

Re: Sharp lc-60le810un power supply

I am not sure what happened, but I seem to be back to where I was stuck before. Maybe I have a bad solder joint in this area. The opto below this one pc7703 only has 0.14vdc between the two terminals on the secondary side. I think I traced this one to the PNL-POW signal. Should I order a few pc123 replacements? I would just replace the power board but I have a bad feeling about the LEDs so I am trying to get this one going without spending a lot on a new board.

[budm]

Re: Sharp lc-60le810un power supply

I do not know what the PC7703 is used for in the circuit, but you should order more than one any way.
You can temporary short the E and C of the switched transistor with a switch so the PFC and the SMPS for the LED driver section will get the VCC to run, you still need to have PS-ON present for the 12vPNL to work.

[crosstalk]

Re: Sharp lc-60le810un power supply

I finally got back to this project. I put a switch on the E and C of the transistor and now I have 400vdc on the main cap and 223vdc on the LED output. I need to put it back in the TV and see what happens in terms of the backlight LEDs.

[crosstalk]

Re: Sharp lc-60le810un power supply

I put the power board back in the TV and the backlights seem to be working when I turn on the shorting switch. I have to use the "force on" button sequence (vol-,chan+,power) for the TV to do anything. The TV turns on, the backlights come on then dim a bit and the TV appears to stay on (standby arrow is solid). Nothing is displayed on the screen--no menu, no "no signal". The t-con appears to have voltages in various places on the board, so I don't think a fuse is blown there.

Am I wrong to expect a picture with the "force on"? Should I be looking for a main board problem now?

[budm]

Re: Sharp lc-60le810un power supply

The PC7703 may be the same as used in this thread for the AC-DET. I will need this thread again to remember what is going on with your TV.
https://www.badcaps.net/forum/showthread.php?t=49486

[crosstalk]

Re: Sharp lc-60le810un power supply

Thank you. Interesting thread about ac-det. Pin 9 (ac-det) is 3.139vdc when everything is connected and I use the "force on." I guess that's on the low side and I should remove pin 9 from the connector housing and tie it high (5v) via a resistor?

There is a small red led (located next to the main processor heat sink) flashing on the main board--any idea what that means?

[budm]

Re: Sharp lc-60le810un power supply

"ac-det. Pin 9 (ac-det) is 3.139vdc " So your AC-DET is OK. I am not sure about the LED on the main board, may be that is normal.

[crosstalk]

Re: Sharp lc-60le810un power supply

After a long wait for the pc123 parts, I replaced PC7901 and the other pc123 optos in the same area. Same results--still 1.02vdc between the pins on the led side of the opto and the PFC circuit isn't switching on. Should I take a measurement of the pads with the opto removed?

The PS-ON signal drops from 4.8vdc to around 0.6vdc at the base of Q7923, which is marked W2X (an npn transistor). The resistors around it seem ok. The diode test from E-B should read OL but it reads 1.8v so I was thinking maybe Q7923 was bad. I tried shorting B-C, but still no PFC boost. So I'm not sure--any thoughts?

[crosstalk]

Re: Sharp lc-60le810un power supply

I removed Q7923 from the board and it tests ok. Does anybody have a schematic for this dps-219 board?

[rwhuggar]

Re: Sharp lc-60le810un power supply

Hello: I have the Service Manual as well the Power Supply if that would help you.

[crosstalk]

Re: Sharp lc-60le810un power supply

Thanks. That would be great. I didn't see a power supply schematic in the service manual I have.

[crosstalk]

Re: Sharp lc-60le810un power supply

So I am finally getting back to this TV. After more testing, it looks like the main board is the problem (short on 1.8v power rail). I figured out there is a signal labeled STB that the main board asserts to fully turn on the power supply. After asserting that signal, the power board works fine.

I checked for shorted MLCC bypass caps and didn't find anything. I am now suspecting a bad video processor. Seems unlikely that the bga pads developed a short vs. an internal short in the processor. Any use in trying to heat the processor to reflow the bga connections? Don't think removal/rework is in the cards for this.

[crosstalk]

Re: Sharp lc-60le810un power supply

Thanks for the help with the power supply and testing. I got this one fixed with a new main board.

[thoma]

Re: Sharp lc-60le810un power supply

Can you upload schematic dps-219?
please!

[crosstalk]

Re: Sharp lc-60le810un power supply

Sorry I don't have a schematic for the power supply