Element ELCHW321 Catastrophic Failure

[budm]

Re: Element ELCHW321 Catastrophic Failure

Check the DC voltage on that C841, C844, Gate voltage of MOSFET V812 (this voltage should toggle when TV is turned on and off).
BTW, if you flex the board, does it make the difference?

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

I've tried pushing on the board while in place and it made no difference.

Will check those voltages.

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

bud I rechecked and have a good 12v supply. The 5v supply is at 1.35v so I checked at V813 and (if I have the pins right...) have

G=12.4v
D=5v
S=1.35v

Does that mean the mosfet is bad ?

[budm]

Re: Element ELCHW321 Catastrophic Failure

G=12.4v
D=5v
S=1.35v

That cannot be right, to get 12V output at the S pin of the MOSFET V812, the D should have more than 12V, that D pin is connected to the power supply that has filter cap C844 (1000UF 25V) which is the one that provides 12V power for the MOSFET. See SCH.

"bud I rechecked and have a good 12v supply" Which 12V is that in the diagram? Since S pin only shows 1.35V how do you get good 12V OK?

[vinceroger69]

Re: Element ELCHW321 Catastrophic Failure

buds mentioning v812 your are testing v813? just to comfirm

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

That is correct vince, I am testing V813 as my 5v rail is low. I assume all is good with V812 as I have 12v supply at the connector (output to main board)

[budm]

Re: Element ELCHW321 Catastrophic Failure

Yes, I am asking about V812 since post 41, it is the MOSFET for switched power supply which you had indicated that you do not have either switched 12V or switched 5V. The switched 5V which is supplied by MOSFET V813, it is turn on when switch 12V is turn on, then that 12V output is used to bias on V813.
So you are telling me now that the switched 12V is working but the switched 5V is only putting out 1.35V?
It is really confusing now since all along I thought you do not have either switched 12v or switched 5V.

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

I do apologize bud, you have it correct. Switched 12v line is outputting 12.4v and is also seen at the gate of V813. However its output is only 1.35v

Should I remove the 5v supply pins from the connector to see if the main board is pulling down the supply or should I replace the mosfet V813 ?

[vinceroger69]

Re: Element ELCHW321 Catastrophic Failure

i only noticed after reading the whole thread theres some good fault finding tests as im still learning reading these sort of threads helps me to understand the psu a little more as budm explaines it so its easy to understand i hope you manage to fix the psu.

[budm]

Re: Element ELCHW321 Catastrophic Failure

OK, now I understand, so you have only 1.35V instead of 5V, since the Gate is getting enough voltage o bias on V813 then it may mean that the MOSFET is bad, or too much load is on that switched 5V output. Does the V813 get very hot? If not then it can be just bad MOSFET. You can disconnect that switched 5V out put wire and use 10 Ohms (or 15 Ohms) 5W to simulate the load and see if the output will stay at 5V (the power supply is rated at 5V 0.5A).

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

Thanks bud, will report back later.

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

Pulled the pins and have 5.18v at the connector. I don't believe I have a resistor of that size to test with dummy load as you suggest but will have a look soon.

[budm]

Re: Element ELCHW321 Catastrophic Failure

You can use combination of resistors connected in series or parallel just to get close enough to 10 Ohms ~5W. What do you have?

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

Nothing loose I will have to look over some boards that are buried around here.

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

I have a mind to change out the mosfet only because the seller said it wouldn't power up his tv either. So either the mosfet failed or he had a similar problem with his main board that I might have with mine. Chances are...

[budm]

Re: Element ELCHW321 Catastrophic Failure

You can take a chance by setting your meter in DC AMP mode, then put the probes on the S and D pin so it will show the current draw on that switched 5V output, I would suggest soldering the wires to the board and attach them to the meter because I do not want to take chance of slipping probes.

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

In parallel with the mosfet itself ? I thought the probes had to be in series to measure current.

[budm]

Re: Element ELCHW321 Catastrophic Failure

The meter will basically bypass the MOSFET, you will connect the meter AFTER the 12V is on.

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

Ok so pull the probe and put it in Amp spot on meter. Set range to Amperes. Turn on tv and fix probes to S and D. Is it ok to put one probe on S or D and touch the other after power up ?

[mmartell]

Re: Element ELCHW321 Catastrophic Failure

That IS the proper way, right ?