Element ELCHW321 Catastrophic Failure

[newtothis]

Re: Element ELCHW321 Catastrophic Failure

If so here is a schematic

[Tvbob]

Re: Element ELCHW321 Catastrophic Failure

The TV's household's AC supply was struck by lightning,Save yourself time and money buy a board... you may need a tuner (main) board as well. good luck

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

If so here is a schematic

Hey, thanks for that.

The TV's household's AC supply was struck by lightning,Save yourself time and money buy a board... you may need a tuner (main) board as well. good luck

Well the tv is more of a learning project but def thanks for the heads up.

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

I have identified some faulty components so far and removed them.

two resistors - open
two mosfets - shorted
blown capacitor - missing lol
fan7930 - paritally melted/broken
4A fuse

One of the resistors is the white square type (cement?) It is marked "3W 0R15K" which confuses me because without the "K" that would be 0.15ohms but is it really 15k ohms ? According to the schematic in post#21 this is a "0.22 2W" resistor so I'm at a loss.

I'm trying to put together a part order so I can move forward. Any help is appreciated!

[PL519]

Re: Element ELCHW321 Catastrophic Failure

this is definitely 0.15 ohms / 3 watt and should be replaced by a resistor of the same type. It measures the source current of the mosfet to give a feedback to the pfc controller ic. Don´t forget the bridge rectifier as i mentioned before, replace it even if it measures o.k.

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

I'm looking for a replacement for the FAN7530.

Does anyone know if the FAN7930 is a drop-in replacement ? There are four flavours - the CMX, the BMX, the M and the MX.

Any help is appreciated.

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

Instead of searching for many replacement parts in the hopes of repairing the board only to find the panel or main defective I've purchased another power supply for a few dollars which is also defective.

However I do get the standby supply and when I heated the board the set came on and functioned normally.

I can no longer force it on with heat so I can't pinpoint the faulty component this way.

I've pulled the PSON pin and measure 5.3v. When connected it is 2v. I believe this line to be active high so I think the main is trying to turn on the PS.

Would really love to learn at the schematic level how to troubleshoot this (schematic in post#21).

PSON (pin12 labelled as "STB") splits off, one to one of the optocouplers and the other not sure where. I *think* the signal turns on both the 5v and 12v lines separately ???

Tell me where to put my probes and what to look for but if you're feeling generous please tell me WHY so I can begin to understand HOW some of these circuits actually work.

[Alastair E]

Re: Element ELCHW321 Catastrophic Failure

Not that I know--That exact PSU.....

LCD PSU's generally have three main sections, The PFC, the STBY-5V and the Main Supplies section.

The PS-on generally activates the Main, and derives the 12 and 24V rails, and any additional 5 or 6V rails depending on the supply. In the case of yours with the BL as part of the PSU, that would be activated too

Often these 'Main' rails are all developed by the same Main section, with its own transformer itself driven by its own MOSFET (S) and control chip....

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

Right I have Standby and power-on signal so what is preventing the supply from coming up ? How to troubleshoot ?

[budm]

Re: Element ELCHW321 Catastrophic Failure

Check the DC voltage on the main filter cap C810 legs when TV is in standby and when it is turn on. We need to find out if the PFC circuit is working or not.
Check or replace C822, C828, and C830, C809 (for VCC for the PFC IC).

[stj]

Re: Element ELCHW321 Catastrophic Failure

any switching psu that runs when warm, but cant start from cold is almost always a small startup cap.
usually 4.7-47uf in value.

c809 or 822 or 860 maybe

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

Check the DC voltage on the main filter cap C810 legs when TV is in standby and when it is turn on. We need to find out if the PFC circuit is working or not.
Check or replace C822, C828, and C830, C809 (for VCC for the PFC IC).

budm voltage at main filter cap is 387v. I have checked those capacitors and they look good with my esr meter. Is there a way to look deeper before just replacing caps ?

[budm]

Re: Element ELCHW321 Catastrophic Failure

That is fine, the PFC is working so that means the standby power supply is working right now? I thought you have to heat up the board to get the standby power supply section to come on.

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

No, standby works fine. When I heated the board the secondary voltages came on and the tv worked as normal. That doesn't seem to work anymore and the caps you suggested check out fine on my meter. What next ?

I did check the voltages across the caps C822, 828 and 830. C828 and C830 had 16-17v on them. C822 had under a volt so the FAN7620 is not receiving vcc ?

[budm]

Re: Element ELCHW321 Catastrophic Failure

"C822 had under a volt so the FAN7620 is not receiving vcc" That cannot be since that is the VCC for running the IC N801 (FAN7602B) for the standby 5V and the switched 5V and the switched 12V, otherwise you will not have standby voltage right now and you will not be getting the voltages at C822, 828 and 830.
"When I heated the board the secondary voltages came on and the tv worked as normal" Which voltages are those? the switched 5V and the switched 12V?

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

Yes the switched 5v and 12v came up after heating the board. I cannot repeat it by heating anymore.

Then disregard my voltage readings lol maybe I didn't make contact this was on the top side of the board.

[budm]

Re: Element ELCHW321 Catastrophic Failure

So right now the condition is, you do have PFC voltage (387VDC as reported) but no switched 5V or switched 12V. The switched 5V is controlled by the switched 12V, if 12V does not turn on then there will be no bias to turn on MOSFET V813 for the switched 5V. Check C841.

[stj]

Re: Element ELCHW321 Catastrophic Failure

did you resolder the transformers yet?

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

budm, will check it.

stj, no I did not.

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

C841 checks out good.