Sharp LC-70SQ15 PWB DPS-206EP problem

[budm]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

At this point, it looks like the Boost converter is working but the Q7202 is not getting the DIMOUT (pin 11) drive of the BD9488 to drive the Gate to turn that MOSFET on and off to allow the LED current to flow. Check the resistance between GND and the DIMOUT pin to see if it shows low resistance reading or not. You should also test R7299 (connected to pin 11) and also the resistor connected to the Gate of Q7202, also check Q7202 itself.

[rabitbay]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

At this point, it looks like the Boost converter is working but the Q7202 is not getting the DIMOUT (pin 11) drive of the BD9488 to drive the Gate to turn that MOSFET on and off to allow the LED current to flow. Check the resistance between GND and the DIMOUT pin to see if it shows low resistance reading or not. You should also test R7299 (connected to pin 11) and also the resistor connected to the Gate of Q7202, also check Q7202 itself.

Between DIMOUT and GND got 12.5k
The resistor to the gate R7231 labeled as 2.49k seem ok, with 2.47k

I couldn't find the R7299 I'm assuming you are talking of the jumper resistance R7229, have 0 as labeled

Some days ago I removed the MOSFET to test it out, and couldn't find any faults, but just to double check I removed it again, I've attached the readings. Also no continuity between gate and S on any direction

[budm]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

"Also no continuity between gate and S on any direction"
It is MOSFET, that is why.
https://www.elprocus.com/mosfet-as-a...free-circuits/

No Gate drive for the MOSFET may mean the IC is bad or something is locking out the drive output.

[rabitbay]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

"Also no continuity between gate and S on any direction"
It is MOSFET, that is why.
https://www.elprocus.com/mosfet-as-a...free-circuits/

No Gate drive for the MOSFET may mean the IC is bad or something is locking out the drive output.

Yeah!! After trying to test it on ON state, both of the MOSFET was not Closing, so Both MOSFET are OPEN ??
I will replace them an tell you what happend

[rabitbay]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

Well, this is not going good, I did changed the MOSFETs and still is in black.

Still have 0v on DIMOUT not even a peak when I plug to AC, now I'm really lost.

Ok but now something weird happened, when I connect my positive probe to
PWM1 or PWM2 the LED's turned ON, well that's a progress I guess, but I thought that the driver DIMOUT was controlled by ADIMM, and Why is this happening, I've attached some pictures, you can see the backlight through the holes
Can I hook up everything to test it out?

[budm]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

The Backligts can be dimmed by ADIM (Analog dimming control by varying the DC level), the PWM1 and 2 are for the Pulse Width Modulation dimming scheme by varying the pulse width, it will be setup for one or the other, not both. Most TV use PWM Dimming control. You board uses the word DIMMER and you do have >3V that DIMMER pin of the PD pin, so this one may be using Analog dimmer setup.
MOSFET Q7201 is for boost converter circuit as explained before and it is OK otherwise you will not have that Boosted Voltage so I do not understand why you replace that one.

[nomoresonys]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

Well, this is not going good, I did changed the MOSFETs and still is in black.

Still have 0v on DIMOUT not even a peak when I plug to AC, now I'm really lost.

Ok but now something weird happened, when I connect my positive probe to
PWM1 or PWM2 the LED's turned ON, well that's a progress I guess, but I thought that the driver DIMOUT was controlled by ADIMM, and Why is this happening, I've attached some pictures, you can see the backlight through the holes
Can I hook up everything to test it out?

Check bottom of board for any bad/cold solder joints.

[rabitbay]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

The Backligts can be dimmed by ADIM (Analog dimming control by varying the DC level), the PWM1 and 2 are for the Pulse Width Modulation dimming scheme by varying the pulse width, it will be setup for one or the other, not both. Most TV use PWM Dimming control. You board uses the word DIMMER and you do have >3V that DIMMER pin of the PD pin, so this one may be using Analog dimmer setup.

Yes I understand that

MOSFET Q7201 is for boost converter circuit as explained before and it is OK otherwise you will not have that Boosted Voltage so I do not understand why you replace that one.

Just in case

[rabitbay]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

Check bottom of board for any bad/cold solder joints.

It reads 45v AC from HOT to COLD just to verify, is that normal?

[Davi.p]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

Hi, you have changed Q7201, but if it was failed also the Rs will be failed, that one connected to pin 11 CS of the IC and to the source of Q7201.

[rabitbay]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

Hi, you have changed Q7201, but if it was failed also the Rs will be failed, that one connected to pin 11 CS of the IC and to the source of Q7201.

I agree with you, I appreciate your answer, do you know some technique to check if it has the right values?, for Rs just by reading the number, but in the other components

[budm]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

Q7201 is for the boost converter and you DO HAVE 268V per your post #17 LED boosted Voltage, PWM Controlled Q7202 is the one that is not getting the drive to turn it on.
So are you saying now that you no longer have LED boosted Voltage?

[Davi.p]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

Rs is less than 1ohm, don't know how much. Yes i have forgot you have a boosted tension for an instant, have you tested the power diode? It is maybe that one in TO220..

[rabitbay]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

Rs is less than 1ohm, don't know how much. Yes i have forgot you have a boosted tension for an instant, have you tested the power diode? It is maybe that one in TO220..

I'm thinking to make a video, so I can show you better, because I'm starting to think that I'm misunderstanding some points or maybe or maybe I am misjudging some testings.

So some points I'm gonna cover is:

Voltage tests on LED pins
Voltage peak on LED pins when tv is turned on
Returned voltage on each strip
PMW effect of multimeter probe when testing pin 5/6 on LED driver

[rabitbay]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

After trying to make a small simulation of the OpAmp IC7202, the simulator gave me the same values on pin 3 and 2, but on reality I have very difrent values,


PD: I didn't find the TO220

[Davi.p]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

I mean D7216 if i see well..

[rabitbay]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

I mean D7216 if i see well..

I remove it to check it out, and it's ok, no short or open on any of both diods

[Davi.p]

Re: Sharp LC-70SQ15 PWB DPS-206EP problem

there was no need to remove it..