LG 42LG70 blowing fuse

[tibimakai]

Re: LG 42LG70 blowing fuse

I couldn't find it on Digikey.

[budm]

Re: LG 42LG70 blowing fuse

Right now the fuse keeps blowing is due to shorted out MOSFET's, not due to high inrush current.
Please leave the two MOSFET's out for now and check the DC voltage on the main DC filter cap, check the voltage when the TV is OFF and when the TV is ON (PFC circuits kicks ON).

[budm]

Re: LG 42LG70 blowing fuse

Fuse, just serach for '3.15A 5x20mm fuse'
http://www.digikey.com/product-detai...543-ND/1009769

By the way, did you check those two MOSFET's and the two Diode in the PFC circuits mounted on the heat sink?

[tibimakai]

Re: LG 42LG70 blowing fuse

Thank you for the fuse, I will buy them.
I have checked(as I know how, but still not sure how) the two transistors and two diodes on the heat sink and they seem OK.
I have removed the two transistors and the short is gone. Inserted another fuse and started it up and I have 385V and 5.1V STBY(switches are lighting up and they beep).
When I turn the TV off the 385V the voltage drops to 161V.
After plugging in the AC cord, the voltage is already at 385V without turning the TV on from the switch or remote.

[budm]

Re: LG 42LG70 blowing fuse

OK the PFC is working and not putting too high of the voltage to damage the MOSFET's. Do not install the MOSFET yet, with TV off, but still plug in, check the Gate's pads of both MOSFET's on the board to see what kind of DC voltage you have on the GATE's pad.

[tibimakai]

Re: LG 42LG70 blowing fuse

Both are oscillating, one a lot more then the other.
One is 13.5V with a bit of oscillation, but the other it's hard to tell, because it's oscillating between 0-4.3V(the highest that I have seen).

[budm]

Re: LG 42LG70 blowing fuse

I do have one question to ask on the sequence of the event: it was blowing the fuse, you found shorted out MOSFET's so you replaced both MOSFET's. The fuse blown right away, so you install the new SMPS IC but did not replace the two new MOSFET's. So now we found out that the new MOSFET's are blown again. Is this correct? If it is, this is what I think what is going on, when the original MOSFET's blew up, it also damaged the SMPS IC. So when you replaced the MOSFET's without replacing the IC at the same time, the damaged IC took out your new MOSFET's, then you replaced the IC but you did not replace the new MOSFET's that were shorted out, so now the shorted MOSFET's took out you new IC.

[budm]

Re: LG 42LG70 blowing fuse

If I have the board in front of me right now, I would replace the two MOSFET's, the IC, and fuse, then plug the TV in the current limiter using lamp and see what will happen.

[tibimakai]

Re: LG 42LG70 blowing fuse

Yes, that is how it happened and I think that you are right(as always) with the rest also.
I will have to order a new IC and fuses. Transistors I have ordered just in case.
Thank you for your help, I appreciate it a lot.
I won't "bother" you for a week, I will be back on 08/19 from Costa Rica.
Hopefully I will get the parts from China also for the Samsung monitor.
It will be exciting when I will get back, I'm also waiting on an inverter transformer for a Sony TV, so if everything goes well, I will have three working devices(two, thanks to you).
I still have that Asus monitor and a Philips 42PFL7422D/37 w/no power, no relay click.

[budm]

Re: LG 42LG70 blowing fuse

Vacation? By the way, check the resistors, diodes, cap around that IC also, remember the monitor that we still cannot figure out what is going on due to burnt out resistors in the Gate drive circuits?

[tibimakai]

Re: LG 42LG70 blowing fuse

Yes, we are going for a week since my daughter is in vacation now.
I will check those components also.
Yes, that monitor. I have replaced the IC, the resistors, but I have a feeling that the IC doesn't get enough voltage(only 142V). I have updated that post a couple of days ago with the latest voltages. I haven't tried out with the 200K resistor yet, as suggested by another member.
And I still have that Vizio VO42L which seems in order, but still won't start.

[budm]

Re: LG 42LG70 blowing fuse

Oh by the way, there are version A and version B for that SMPS IC, make sure to match the version. See page 13

[tibimakai]

Re: LG 42LG70 blowing fuse

It's AG, thank you for looking out for me.
This is the one I have purchased and I'm considering buying again:
http://www.digikey.com/product-detai...SCT-ND/1646500

[tibimakai]

Re: LG 42LG70 blowing fuse

I have finally replaced the IC, the two FET transistors and the fuse and now it blew the main fuse.
At the main capacitor it shows short. Removed the FET closer to the fuse and the short is gone.
I have to confess that I haven't checked all the components as we agreed.
It can't be the transformer's winding shorted?

[tom66]

Re: LG 42LG70 blowing fuse

All transformer windings will read DC short, what matters is inductance and Q factor.

[tibimakai]

Re: LG 42LG70 blowing fuse

FETs should be handled with grounding strap? I'm thinking,what if I handle them wrong and they are already shorted when I install them?
Anybody can teach me please how to test these FET transistors?

[Th3_uN1Qu3]

Re: LG 42LG70 blowing fuse

Switching MOSFETs are pretty resistant to ESD, there is no problem in handling them. There's something else gone downstream. Get a habit of using this whenever you are dealing with a device that had blown mains fuses, it will save you a lot of blown parts.

http://antiqueradio.org/dimbulb.htm

[tibimakai]

Re: LG 42LG70 blowing fuse

Yeah, I have the components for it, I just didn't have the time yet to put it together.
By the way, what kind of bulbs I should use, same as in the description, have different wattage and go from low to a higher one?
Just got back from vacation and I was excited to see it running and rushed it.
I just don't understand why the two FETs are open right(see my other picture with the red line marked) after installing them without power applied.

[budm]

Re: LG 42LG70 blowing fuse

For 42" TV, at least 100W.

[tibimakai]

Re: LG 42LG70 blowing fuse

You are right, they use at least 240W.