LG 37LS5600 blows main fuse

[dimis7]

Hi all,

Need some advice to troubleshoot this TV.

PSU blow the main fuse F100, 3.15A.

I replace the fuse with another 3A (but not ceramic) and blows it again after few seconds when i plugged in to the wall, with nothing connected to PSU, just the power cord.

I checked with DMM for dead sorts but didn't found any.

Checked bridge rectifier and seems ok.
Also check main filter cap with transistor / cap / esr tester (the usual cheap transistor testers from ebay) and found ok.

PSU p/n is EAX64405901 (1.6)
LG p/n is EAY62569601

Pictures attached.

Appreciate if anyone can help.

Thanks.

[nomoresonys]

Re: LG 37LS5600 blows main fuse

if you have not, maybe check, looks like Q601, check that theres no shorts from any leg to the other 2, not a complete test but they usually fail short, I would check all the diodes and resistors too, easier stuff first. all of those will be done with tv UNPLUGGED from power.

[nomoresonys]

Re: LG 37LS5600 blows main fuse

building one of these for a few bucks will keep from blowing fuses and components up for easier troubleshooting: https://www.youtube.com/watch?v=k5oNQ1etN2c

[dimis7]

Re: LG 37LS5600 blows main fuse

Q601 and most, if not all, transistors and diodes are checked and are not shorted. Not checked all resistors yet, its a little bit difficult to read the color code but I will do it.

I know about the trick with the lamp, maybe I will try to build it if I can find a incandescent lamp

[lotas]

Re: LG 37LS5600 blows main fuse

Check varistor.

[dimis7]

Re: LG 37LS5600 blows main fuse

Checked. Its not shorted. Reading 1.2MOhm in circuit.

[nomoresonys]

Re: LG 37LS5600 blows main fuse

guess that leaves the two 3 pin diodes to check, sticking out of the heatsink there.

[dimis7]

Re: LG 37LS5600 blows main fuse

.

Are you sure? It's between live and neutral. 10 Ohm it's almost short circuit...

[nomoresonys]

Re: LG 37LS5600 blows main fuse

lol, I got your mov confused with the ntc, your mov looks good.

[nomoresonys]

Re: LG 37LS5600 blows main fuse

maybe pull up the datasheet on IC501, wonder if its shorted or malfunctioning??

[nomoresonys]

Re: LG 37LS5600 blows main fuse

then theres the 2 optos, ic502, ic503, what else is left to test?

[dimis7]

Re: LG 37LS5600 blows main fuse

Ic501 is 3BR4765JZ. There is very low resistance between pins 3 and 8 (2.3Ohm). I believe it's ok as per datasheet and created by R510 and R511 resistors.

Of course don't know if the chip itself is ok or not...

Optocouplers also not shorted.

[R_J]

Re: LG 37LS5600 blows main fuse

Check the resistance between pins 3 and 5 of ic501

[dimis7]

Re: LG 37LS5600 blows main fuse

It's about 3,5MOhm

[R_J]

Re: LG 37LS5600 blows main fuse

That value seems to be ok so the ic "might" be ok. And with nothing else connected, the board should just be in standby. Check D201, D202, what do they read in diode test?

[dimis7]

Re: LG 37LS5600 blows main fuse

Can't find D201 and D202. Maybe you mean D501 and D502 near ic501?

If yes they are reading: D501 with positive lead to cathode nothing.
With negative lead to cathode: 478

D502 with positive lead to cathode nothing.
With negative lead to cathode: 479

There is also D503 near: with positive lead to cathode nothing
With negative lead to cathode 476

[nomoresonys]

Re: LG 37LS5600 blows main fuse

those two are on the bottom/underside of the board.

[dimis7]

Re: LG 37LS5600 blows main fuse

Ok found it.

Both measure 200 one way, slowly rising to 1600 from the other way.