Sharp Aquos LC52SE94U hit by surge

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

Yup that's all done no more short
I traced back the gate circuit and all of the resistor values are good.
Btw when I removed the MOSFET and tested it only the source and drain are dead shorted, there was ~89ohm between G-S and G-D

[budm]

Re: Sharp Aquos LC52SE94U hit by surge

It will be hard to verify if the Gate drive pin of the IC is damaged or not when the MOSFET shorted out, but more likely the IC is damaged due to short between G and D, that 89 Ohms low is enough to dump high voltage of the Drain pin to the output pin of the IC.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

That makes sense to me, I guess the question is the, what qualifying as a short between G-D?

[tom66]

Re: Sharp Aquos LC52SE94U hit by surge

I always replace the driver IC. If you don't, you risk blowing up your new MOSFETs and possibly causing further damage.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

That also makes good sense to me.:-)
I will go back through just to make sure L6552 is the driver and look for a replacement.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

So your board is not the same as the one from Shopjimmy that we were using to troubleshooting your board? it does not have Dual PFC circuits?
I will not taking a chance of installing the new MOSFET without replacing the IC, if the the out put of the IC is stuck on HI (instead of turning the MOSFET ON-OFF), it will cause your new MOSFET to blow, so makes sure to leave the lamp in place of the fuse.
Your picture in post 18 I see two MOSFETs and two PFC diodes though.

Again I missed a post,sorry. Yes it it's the sj board; Tom66 had referenced the RDENCA231wjqz as very similar and since it shares the same physical board I have been using those schems as a reference . The 231 seem to have a singe Pfc circuit while the 235 has a dual pfc circuit as u mentioned but from what I can tell (unconfirmed) is that IC7801 drives both MOSFETs. Don't know if that makes any sense?

[budm]

Re: Sharp Aquos LC52SE94U hit by surge

Looking at YOUR picture (post 20) bottom side of the board, it does have 2 MOSFETs and 2 PFC diodes and 2 PFC ICs.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

Yes 2 identical MOSFETs (IPA60R199CP) Q7808 & Q7805 mounted on sink.

There are 2 ICs in the vicinity, IC7800 ( DAS001/-a TSM103 from what I can gather so far) and IC7801 (L6562D), SMTs

The diodes D7809 &D7806 are identical (ST TH8LO6FP???) and are mounted to sink also.

[budm]

Re: Sharp Aquos LC52SE94U hit by surge

OK, that's what I thought you also have on your board, right now one of the two PFC circuits is bad, shorted MOSFET and possibly bad PFC IC.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

The TSM 103 from what I understand is a dual op amp.
The L6562D is a PFC controller with the gate driver on pin 7.
I traced pin 7 and it feeds both gates of the individual MOSFETs through a 100ohm resistor.
Both gates have a diode and a 43ohm resistor in series with a 10kohm resistor-diode pair grounded on the gate side of the 43ohm resistor.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

OK, that's what I thought you also have on your board, right now one of the two PFC circuits is bad, shorted MOSFET and possibly bad PFC IC.

Right now I am trying to determine if both MOSFETs are driven by the same Pfc controller, which I believe to be the case. I may attempt to draw a schem.

[budm]

Re: Sharp Aquos LC52SE94U hit by surge

You can trace out the Gate pin of each MOSFET to see where it goes to. From what I see, there are driver transistors (Q7804, 7807) for each Gate. Do those two SMD 8-PIN ICs have the same P/N on them? If not then they are not driven by two ICs, which may explain why there are two driver transistors.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

Yes 2 identical MOSFETs (IPA60R199CP) Q7808 & Q7805 mounted on sink.

There are 2 ICs in the vicinity, IC7800 ( DAS001/-a TSM103 from what I can gather so far) and IC7801 (L6562D), SMTs

The diodes D7809 &D7806 are identical (ST TH8LO6FP???) and are mounted to sink also.

No that's the point I'm trying to make -both gates trace back to pin 7 of IC7801 the Pfc controller in the manner I described above.#90

[budm]

Re: Sharp Aquos LC52SE94U hit by surge

Sorry I missed that one.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

Sorry, I kinda carelessly omitted the transistors in post #90. The transistors Q7804 & Q7807 are actually driving the MOSFET gates, correct?
Here's my schem for Q7808, I forgot to identify the IC-7800(L6562D), the other MOSFET(Q7805) is identical to this...

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

Just a question....in order for the driver to be damaged- wouldn't the diode or transistor or both need to be shorted?
Btw I have an L6562 in my cart at Newark anyway $1.29...

[tom66]

Re: Sharp Aquos LC52SE94U hit by surge

Not necessarily - diode and transistor for semiconductors are quite big (on the die scale, process size of say 50um isn't unusual) - this means they can handle a brief overload fine - but the IC usually has a much smaller process so is a lot more vulnerable to damage.

[budm]

Re: Sharp Aquos LC52SE94U hit by surge

That transistor is connected as a clamping circuit to limit the drive to the GATE, the transistor will be bias on when enough current flow through the diode to bias on the E-B junction which in turn turns on the transistor and divert the drive signal from IC to ground. Since you have G-D low resistance, I am surprise that the Zener, transistor, etc in the path back to the drive output pin of the IC are not damaged since those components will not be able to handle the high voltage dump from Drain pin.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

That transistor is connected as a clamping circuit to limit the drive to the GATE, the transistor will be bias on when enough current flow through the diode to bias on the E-B junction which in turn turns on the transistor and divert the drive signal from IC to ground. Since you have G-D low resistance, I am surprise that the Zener, transistor, etc in the path back to the drive output pin of the IC are not damaged since those components will not be able to handle the high voltage dump from Drain pin.

From this I infer that there is a good possibility that this part of the circuit is damaged as well.

[budm]

Re: Sharp Aquos LC52SE94U hit by surge

Yes, there is possibility.