help with schematic or with fixing this pcb

[buchman]

Hi guys,

desperately want to fix that tv. a Hisense 65" led 3D.

Replaced a few components that were damaged (photos attached) and when connected to other boards on the tv it blew the fuse and the FQPF3N80C mosfet. replaced them and it still burning them.

[budm]

Re: help with schematic or with fixing this pcb

Hi guys,

desperately want to fix that tv. a Hisense 65" led 3D.

Replaced a few components that were damaged (photos attached) and when connected to other boards on the tv it blew the fuse and the FQPF3N80C mosfet. replaced them and it still burning them.

What is the designator for that MOSFET you replaced, Q?????
What section of the circuit that MOSFET is used in?

[buchman]

Re: help with schematic or with fixing this pcb

What is the designator for that MOSFET you replaced, Q?????
What section of the circuit that MOSFET is used in?

Yes it's Q.
It is used in the hot section.

[budm]

Re: help with schematic or with fixing this pcb

Q what? 1,2,3, 4, 5?

[budm]

Re: help with schematic or with fixing this pcb

I see V857 is badly blown up.
https://www.badcaps.net/forum/attach...8&d=1518005198.

[buchman]

Re: help with schematic or with fixing this pcb

Q what? 1,2,3, 4, 5?

What do you mean?

[buchman]

Re: help with schematic or with fixing this pcb

I see V857 is badly blown up.
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Yes I know. That is after the third attempt I tried to fix the pcb.

[R_J]

Re: help with schematic or with fixing this pcb

You could have a bad N or an open R or shorted VD Usually when those fets short they take out the drive circuit too

[vinceroger69]

Re: help with schematic or with fixing this pcb

What do you mean?

printed on the pcb where the part is fitted it will say something like Q185 if we have a schematic we can then follow its path etc or was it a mosfet etc you replaced with the pcb marked starting with a v

[buchman]

Re: help with schematic or with fixing this pcb

getting a read of 0.04 on that component. It say T4 on it.
can't figure out what can make him do that.
soldered it out and it was ok, it read 0.521 on diode mode.

[buchman]

Re: help with schematic or with fixing this pcb

printed on the pcb where the part is fitted it will say something like Q185 if we have a schematic we can then follow its path etc or was it a mosfet etc you replaced with the pcb marked starting with a v

on the pcb it says V871.
I have replaced that with the same mosfet which is FQPF3n80c

[buchman]

Re: help with schematic or with fixing this pcb

You could have a bad N or an open R or shorted VD Usually when those fets short they take out the drive circuit too

What are these letters stand for?

[R_J]

Re: help with schematic or with fixing this pcb

Exactly. See if you don't put the location number after the letter they mean nothing, Like `Q' Your burnt fet is labled V857, the part you are measuring in post #10 is VD837
The `N' that I refered to is N871, (the ic) The R, would would be to check the resistors that are connected to the fet's Gate pin like R861, R860, R859, etc.
You might also want to check the diodes on the secodary like VD838, VD842 etc.

[buchman]

Re: help with schematic or with fixing this pcb

Exactly. See if you don't put the location number after the letter they mean nothing, Like `Q' Your burnt fet is labled V857, the part you are measuring in post #10 is VD837
The `N' that I refered to is N871, (the ic) The R, would would be to check the resistors that are connected to the fet's Gate pin like R861, R860, R859, etc.
You might also want to check the diodes on the secodary like VD838, VD842 etc.

First of all, thanks a lot for your help.
second, you were right, I have replaced the N871, the 3 resistors
and now my problem is the reading of the VD837.

[buchman]

Re: help with schematic or with fixing this pcb

what are these letters mean?
I know that R is for
L for coil
D for diode
C for caps.
But what is VS or N or VD etc.
where can I get information about each letter?

[buchman]

Re: help with schematic or with fixing this pcb

You might also want to check the diodes on the secodary like VD838, VD842 etc.

Tested them all and they are ok.

[R_J]

Re: help with schematic or with fixing this pcb

Thats just what this manufacturer uses, normally integrated circuits are "ICxxx" these guys are using N. for ic's VD for diode and looks like VZ for Zener diode.

[buchman]

Re: help with schematic or with fixing this pcb

So guys, what are you saying? what can cause the diode VD837 show a reading of 0.040 instead of 0.520 when it's out of the circuit?

[R_J]

Re: help with schematic or with fixing this pcb

Try removing the shorted V857 from the circuit for starters, the one with the hole in it.
If the diode still checks like that It could be that the drive ic (N871) is internally shorted
There are also a couple resistors in that circuit, one could be a low value (like 68 ohms) in parallel with it.
What is the number marked on the N871 IC?

[buchman]

Re: help with schematic or with fixing this pcb

Try removing the shorted V857 from the circuit for starters, the one with the hole in it.
If it still checks like that It could be that the drive ic (N871) is internally shorted
There are also a couple resistors in that circuit, one could be a low value (like 68 ohms) in parallel with it.

I have a pcb just like that (I have ordered and it came broken and now I am trying to make 1 out of 2).
I have replaced already every component that was faulty.

What is it mean that one of the resistor value is 68 ohms?

there is a resistor like that. He is ok.

I have noticed that when I test for continuity on some of the resistor, take make a beep and some of them not. But, when I test for OHMS they show the correct value.