Sharp LC-60E79U problems

[Redrebel10]

Re: Sharp LC-60E79U problems

Thanks so much bud, it's my personal tv to put on my back porch so I'm just soldering the resistor and using it like this, your help is greatly appreciated

[budm]

Re: Sharp LC-60E79U problems

Here is how I added the 330ohm resistor

if you plan to use it that way, you should solder the leads.

[shelby5041]

Re: Sharp LC-60E79U problems

hi i have a sharp LC-60e79u that had an extremely slow picture refresh

and screen turned white....and picture was super super grainy and light washed out

im parting it out if you need any parts that may be good

[budwich]

Re: Sharp LC-60E79U problems

certainly good news.... maybe this will work for a few of those "other threads" with similar looking problems... :-)

[budm]

Re: Sharp LC-60E79U problems

It will need more indepth troubleshooting in that GATE drive circuit. I will have to look at real good clear closed up pictures around that Gate pin to see how it is driven, or we can use the added inverter circuit to take the BL-ON (STB pin?) signal to turn it into active low to control that MOSFET.

[Redrebel10]

Re: Sharp LC-60E79U problems

Here is how I added the 330ohm resistor

[Redrebel10]

Re: Sharp LC-60E79U problems

Good News Bud using a 330 ohm resistor, I twisted one end around the gate pin of Q7120 and put the other end under the closed screw that mounts the psb, PNL12 immediately went to 11.9v and the tv came on, I initially did hard start-up (vol down and Input) and it came with the that service blue K on the screen. I turned it off and turned back on and it works perfect. So now just have to figure what controls the gate voltage or I can just solder a resistor to the gate and call it good.

[budm]

Re: Sharp LC-60E79U problems

Looking at the MOSFET front side with legs down, the left pin is GATE, middle pin is DRAIN, right pin is Source. The +12V is fed to Source pin, the +12V out is the Drain pin, the GATE pin has to be about 4V below the Source pin to turn on the MOSFET (P-Channel), there is a transistor connected to the GATE pin that is supposed to take that GATE pin toward GND to turn on the MOSFET when PNL-POW is high (>2VDC).

[Redrebel10]

Re: Sharp LC-60E79U problems

Ok and I think I made a mistake by calling the gate pin the middle pin, Isn't the gate on the left and the drain pin in the middle? Also I found a post on the internet talking about the same problems and changing IC1101 (same IC mentioned in post 5 of this thread) on bottom on main board was a suggested fix for no voltage going to PNL-PWR so if the resistor jumping gate to ground works, I guess I will try and find that IC1101 which I looked and it might be hard to find. I will follow up tomorrow.

[budm]

Re: Sharp LC-60E79U problems

You can leave the PNL-PWR wire in place sine we are forcing the MOSFET on after the Transistor that drive the Gate pin.

[Redrebel10]

Re: Sharp LC-60E79U problems

OK thanks, I will be trying all your suggestions tomorrow since I work doubles every weekend.

Last night when I got home I started the tv in hard start up (vol- / Input) and once again I got 3.2v on the PNL-PWR, so I checked voltages again. q7120 still reads 12v on both outer pins and .7v on drain pin (same reading on PNL12v) when I was checking the drain pin I may have touched the gate at the same time and I noticed the voltage start rising and it got to 9.4v before it immediately dropped. When it dropped it stopped at .5v, which is now the new reading on the PNL12v pins. I unplugged the cable to tcon and once again the voltage dropped to zero.

I still need to solder in a resistor to the gate tomorrow but my main concern was do I need to cut the pnl-pwr wire to the main board even though I can get 3.2v in hard start up mode.

[budm]

Re: Sharp LC-60E79U problems

The main board generates all the required signal to control the power supply board.

"Are you wanting me to solder a resistor from the gate (middle pin) of q7120 to the chassis as a ground?" Yes.

[Redrebel10]

Re: Sharp LC-60E79U problems

OK, so does the circuit that controls pnl-pwr come from a problem with the main board or can it originate on the psb? Are you wanting me to solder a resistor from the gate (middle pin) of q7120 to the chassis as a ground?

[Redrebel10]

Re: Sharp LC-60E79U problems

Which circuit is responsible for the gate?

[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.

[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.

[Redrebel10]

Re: Sharp LC-60E79U problems

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

[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

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

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