Sharp Aquos LC52SE94U hit by surge

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

Although I realize that in circuit testing of components draws limited conclusions, is there prudence in taking comparative measurements from an identical circuit like Q7805 or a known sample like the Q7805 circuit in another board?

[budm]

Re: Sharp Aquos LC52SE94U hit by surge

Yes that will be one way, that Zener on the Gate and Source will be one of the component that will more likely to be damaged.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

The two Zener surge diodes D7807 ( on MOSFET Q7805-good) and D7811(on MOSFET Q7808-bad removed) diode test with my fluke 83 as:

D7807
Rbias .900v
Fbias .712v

D7811
Rbias .902v
Fbias .679v

Is there any value to these measurements?

[budm]

Re: Sharp Aquos LC52SE94U hit by surge

You will need to test them off the board due to 10K resistor is connected in parallel, it should test like Diode in Fbias, and open in reverse bias until the reverse voltage is higg enough to reach Zener break down voltage.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

That's what I thought, ok thanks!

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

Just the power supply board and the AC input filter board, the relay (RL7001) is turn on by the main board to by pass the inrush current limiters thermistors (TH7000/7001) otherwise the standby power supply will get the voltage through those two thermistors and it should run if there is no shorts circuit.

Should that relay be NO or NC ?

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

I know it might seem like an insignificant question but I noticed the relay is NC which to my thinking means initial or inrush current is bypassing the thermistors,

Am I looking at this all wrong?

Or does the coil energize as soon as power is applied??

[budm]

Re: Sharp Aquos LC52SE94U hit by surge

The relay is N.O. so the in stand by the current will flow through those two Thermistors (The Thermistor is probably rated at about 3~5 Ohms), when TV is turned on, the Thermistor will be bypass (the relay is turned on by the command from the main board., if not the Thermistors will get hot and can burn out. If you check the resistance between the two contacts of the relay, it should show some kind of the resistance.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

Thanks Bud, ya I get around 3 ohm which is the same across the thermistors- BECAUSE they are in parallel...
Feel kinda silly now but at least I understand...

I will go immediately over to general discussions and request an icon for brain fart!

[budm]

Re: Sharp Aquos LC52SE94U hit by surge

They look like in series to me unless the picture is fooling my eyes. May be you mean in parallel with the N.O. relay contacts.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

They look like in series to me unless the picture is fooling my eyes. May be you mean in parallel with the N.O. relay contacts.

Yes that's exactly what I meant Bud, thermistorS meaning both, in parallel with a set of NO contacts not only am I learning to effectively troubleshoot -but also to communicate... The shame continues.....

[budm]

Re: Sharp Aquos LC52SE94U hit by surge

You are already learning well that you are able to draw the schematic of the Gate drive section.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

Ok so in my idle time while waiting on parts to move this thread along, instead of worrying about the damaged power supply, I have decided to try and understand these SMPSs better.
Have Read about buck, boost, buck boost, and MOSFET drive stategies but really needed to get back to basics so I'm over at the PSU forum reading and following links left there by the wise participants.
One question keeps bugging me though- I know this thread may not be the appropriate place to ask but- in this RDENCA235WJQZ SMPS are there two individual PFC circuits or just one using two synchonized MOSFETs to share the load of driving two inductor modules in parallel?

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

Parts have arrived!
Was having so much fun trying to analyze the circuits...

[tom66]

Re: Sharp Aquos LC52SE94U hit by surge

They use the two inductor setup and run the inductors 180 deg out of phase with each other.

This essentially doubles the switching frequency and reduces radiated and conducted noise (a big concern with modern power supplies - regulations are very strict.) It also improves efficiency. I expect it probably ends up costing less, too, which is the main driving factor in consumer electronics.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

Tom I don't know if you remember, but this board shares similarities with the RDENCA231WJQZ that you had( we discussed a while back), anyway been relying heavily on that SCH for reference. One difference is it has no second Q7808 MOSFET or L7802 coil.
Getting to the point, I can see how the the inductor(s) are coupled and that seems to feed back through a transformer seemingly to provide a reference for the L6562D controller etc.
What I can't understand is if the coils are 180 out of phase then why are the windings coupled and shouldn't one MOSFET gate drive be inverted? Both gate drives seem to be in parallel with pin 7 of the L6562D.

[budm]

Re: Sharp Aquos LC52SE94U hit by surge





The drive from the PFC IC, one of it may be get inverted to produce 180deg out of phase drive signal

[tom66]

Re: Sharp Aquos LC52SE94U hit by surge

If it does not drive them inverted, it's just essentially a way of putting two PFC circuits in parallel, reducing the individual requirements for an inductor or MOSFET.

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

If it does not drive them inverted, it's just essentially a way of putting two PFC circuits in parallel, reducing the individual requirements for an inductor or MOSFET.

...and possibly boosting the output power as compared to the 231?

[Fwrothy]

Re: Sharp Aquos LC52SE94U hit by surge

If it does not drive them inverted, it's just essentially a way of putting two PFC circuits in parallel, reducing the individual requirements for an inductor or MOSFET.

...and possibly boosting the output power as compared to the 231?
Would two (if identical) inductors relate to increased current?