Sharp LC-60E79U problems

[Redrebel10]

Re: Sharp LC-60E79U problems

Which circuit is responsible for the gate?

[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?

[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 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

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 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

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

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.

[Redrebel10]

Re: Sharp LC-60E79U problems

Here is how I added the 330ohm resistor

[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.

[budwich]

Re: Sharp LC-60E79U problems

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

[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

[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.

[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