Sharp LC-60E79U problems

[Redrebel10]

Re: Sharp LC-60E79U problems

Just to be sure I'm reading DCV with meter set on 200 range?

[budm]

Re: Sharp LC-60E79U problems

yes I see them, the R almost look like diodes and the C7120 is a cap all on the secondary side

Then you should see the that MOSFET right next to those two resistors sitting right next to each other..

[Redrebel10]

Re: Sharp LC-60E79U problems

I thought mosfets were tested off the board and out of circuit so how do I test the q7120 with my meter

[budm]

Re: Sharp LC-60E79U problems

We are testing to see what DCV we have at the 3 pins of the MOSFET with ref. to chassis GND.

[Redrebel10]

Re: Sharp LC-60E79U problems

I get 12v on both outer pins, the middle pin started with voltage but when I touched it the voltage dropped, all this was done with me forcing the backlights on, on normal start up the psb shuts down after 2 or 3 seconds

[budm]

Re: Sharp LC-60E79U problems

Test it in normal condition with every thing hooked back up because you need to force on the main power supply, and the panel power too not just the backlights circuit.
What is the P/N as printed on the MOSFET?
It should be P-CH, so right now you have Source pin and the Gate pin at 12V which means the MOSFET is not turned on, the Gate has to about 4V less than the Source pin for it to be on.
You can force on the circuit by connecting 470~1000 Ohms resistor between PNL-POW and standby Voltage to do the force on.
BTW, when you said force on backlights, do mean by using resistor?

[Redrebel10]

Re: Sharp LC-60E79U problems

OK I'll check try that later when I get home from work. Forcing backlights on by starting the whole holding volume down and input while plugging in the ac chord into the tv

[budm]

Re: Sharp LC-60E79U problems

Right now we are not dealing with the backlights circuit but we are trying to get that switched +12V to work so it will supply the +12V to run the T-CON board.
So as long as you have +12V on the Source pin of that switched MOSFET and the Gate drive Voltage (around +8V) to turn on the MOSFET when the PNL-POW command signal is present then it should supply +12V at the Drain pin, if not then we have to find out why.

[Redrebel10]

Re: Sharp LC-60E79U problems

OK powering up the tv normally, both outer pins read 12v and when I touch the middle pin it starts at around 6v and immediately drops upon putting my lead on it. All this had to be done within 3 seconds due to the power board making the clicking noise and shutting down the tv which then it displays the flashing error codes on the front, I'm attaching a picture of the q7120 mosfet, best I can read it says 40P03G1 140 28F, Im going to a friend's tomorrow to get a resistor to try and jump the 2 pins as you suggested, I don't currently have one

[Redrebel10]

Re: Sharp LC-60E79U problems

Here is a clearer picture of q7120

[budm]

Re: Sharp LC-60E79U problems

Here is a clearer picture of q7120

https://www.badcaps.net/forum/attach...4&d=1500602551
The left pin is GATE, the middle pin is DRAIN, the right pin is SOURCE.
So if you leave black probe on the chassis and Red probe on the GATE pin and watch the meter to see if the GATE pin Voltage goes down to less than 10V or not, if it does not change at all then it may be that the circuit is not getting the PNL-POW signal from the main board so you need to move the red probe to the PNL-POW pin and watch the meter to see if PNL-POW goes to>2V or not when the TV is turned on.

[Redrebel10]

Re: Sharp LC-60E79U problems

OK the gate pins go straight to 11.9v volts when powering on the tv. When powering on the PNL-POW pin reads zero, however when that click happens to shut down the tv , the voltage jumps to 2.5 just long enough for me to see it before dropping to zero.

[Redrebel10]

Re: Sharp LC-60E79U problems

I just used a 680 ohm resistor and jumped from BU5V (which reads 5v when powered on) to PNL-POW and nothing changed, TV still shut down after 2 or 3 seconds

[budm]

Re: Sharp LC-60E79U problems

Did you disconnect that PNL-PWR wire going back to the main board first? Otherwise the main board will keep that line low and not allowing it to go high, and you need to keep the meter on the PNL12V will jump up to 12V or not.

[budm]

Re: Sharp LC-60E79U problems

Right now if the only missing signal is the PNL-POWER, the rest of the Voltage at the connector going by the pin names should be something as shown in this thread:
https://www.badcaps.net/forum/showthread.php?t=54228

[Redrebel10]

Re: Sharp LC-60E79U problems

Hey Bud, no I didn't pull the wire from the connector before jumping but I did hold my meter on the PNL12v and it stayed at .7v. I figured it might damage the connector If I removed a wire from it but I can try that tonight I work doubles on weekends so it will be late. I checked the other post and all my readings are good other than PNL-POW.

I saw where you mentioned LDO switched regulator, where is this part and are you suggesting its worth a shot to replace it?

[budm]

Re: Sharp LC-60E79U problems

Your board does not use Switched LDO, it uses the MOSFET as simple electronics switch.

[Redrebel10]

Re: Sharp LC-60E79U problems

Ok thanks I will follow after correctly jumping resistor to PWR-PNL

[Redrebel10]

Re: Sharp LC-60E79U problems

One other thing that comes to mind is initially I tested the PWR-PNL and got 3.2v when I did vol down/input start up which lights up the screen. I also tested q7120 at that time and I still got 12v on both outer pins, but still only had .7v on PNL12v. I could disconnect plug from psb and the pnl12v drops to zero, Is it possible that the .7v reading at pnl12v is somehow back fed from the tcon board maybe from the mother board? If I'm following everything you have been saying, the problem is the q7120.

[budm]

Re: Sharp LC-60E79U problems

If you did see the PNL-PWR for seconds but the PNL-12V did not even jumps up for seconds then for sure there is problem with that switching circuit. That 0.70V may be back fed from the T-CON as you suggested. Also, it looks like the circuit that produce the PNL-PWR is dead since it does switch the signal low and high, so you probably no need to simulate the PNL-POW signal at this point.
I believe the Q7120 is OK but the circuit that drive the Gate of Q7120 is not working.
Q7120 can be forced on by soldering in 330~470 Ohms resistor between Gate and GND to force it on and see when you turn on to see if you will get the PNL-12V or not.