Lg 37LG6000 lcd tv

[oddbodd]

Re: Lg 37LG6000 lcd tv

ZD503 [1N5 223 B] was testing zero both ways in circuit, but on removal seemed OK. On replacing, it tested zero both ways again. Three identical ones on the board test OK in circuit. Also see pic.

Typo, sorry, that should be 1N5 232 B.

[tom66]

Re: Lg 37LG6000 lcd tv

What else is that zener across?

[selldoor]

Re: Lg 37LG6000 lcd tv

A quick power on test, and I'm now only getting 25v on the 400v connector pin1 at P601.

What are you using for the ground /Black lead

[oddbodd]

Re: Lg 37LG6000 lcd tv

What else is that zener across?

I'm not really sure. Does the pic help?

[oddbodd]

Re: Lg 37LG6000 lcd tv

What are you using for the ground /Black lead

I'm using one of the screws that hold the bottom board in place as ground.

[selldoor]

Re: Lg 37LG6000 lcd tv

I'm using one of the screws that hold the bottom board in place as ground.

Quote from budm

"When you work on the primary (hot side), you do not use chassis ground as the ground ref for voltage readings, you use the negative leg of the main filter cap (the 450vdc rating) as the ground ref point for the meter. Also do not touch the heat sinks, it can be part of the primary circuits."

[oddbodd]

Re: Lg 37LG6000 lcd tv

Ah, that would explain it.

Although I'm not sure that I can access the legs of the big caps on this board, whilst everything is plugged in.

I did get ~380v the first time I tested, so must have grounded some other way... I can't remember, offhand.

[Alastair E]

Re: Lg 37LG6000 lcd tv

Normally grounding test-lead to the metalwork of the chassis is good enough....

ONLY when checking the Primary (Hot) side would you need to ground to the neg end of the main reservoir cap (Big high-voltage rated cap, say--400 to 450V 100 to 470uF--cant miss it, some sets have two smaller in parallel) if your SMPS PSU isnt running at all, and you suspect the drive or control-chip, start-up circuit etc....

Reason for this is, the SMPS provides isolation by virtue of the Transformers it has, so readings taken on Primary side while grounded to chassis are meaningless.

All of those smaller 1-100uF 25-50V caps on primary side are worth replacing--as a matter of course, only cheap and good for piece of mind.

[steviewonder]

Re: Lg 37LG6000 lcd tv

Hi to all,
New to this site but with regards to the lg,you will most likely find that freezing IC404 will cure the problem.Its a Hynix nand device,It's possible to cheat if no freezer spray is available by using an inverted tin of deodorant...Handy tip i learnt.
best wishes,
steve

[newtothis]

Re: Lg 37LG6000 lcd tv

Hi to all,
New to this site but with regards to the lg,you will most likely find that freezing IC404 will cure the problem.Its a Hynix nand device,It's possible to cheat if no freezer spray is available by using an inverted tin of deodorant...Handy tip i learnt.
best wishes,
steve

Deodorant?! You mean a FLAMMABLE gas?! Hmmmmm... I will say no more!

[tom66]

Re: Lg 37LG6000 lcd tv

Freeze spray / canned air is flammable too. I learned that the hard way.

Canned air is better because it's a lot less conductive (but not zero conductivity), it comes out colder and it doesn't stink up the place

[oddbodd]

Re: Lg 37LG6000 lcd tv

Thanks for the info, everyone.

I'll check out IC404, but I've not got any canned air. I could put the whole board in a freezer bag, and place it in the freezer for an hour or two...

I realise that this won't isolate the problem to IC404, but it might confirm that this board is the one with the problem.

[oddbodd]

Re: Lg 37LG6000 lcd tv

There is no IC404 on this board.

The set just powered on first time, as it's very cold at the moment. Not the second try, though.

I've now brought the set into a warm room, and left the bottom board in the cold for a while, to try again later.

[steviewonder]

Re: Lg 37LG6000 lcd tv

It sits just to the left of the tuner on the pcb I have here,
which is a eax391 001(14)

[oddbodd]

Re: Lg 37LG6000 lcd tv

It sits just to the left of the tuner on the pcb I have here,
which is a eax391 001(14)

Should that be EAX39192001(14) ?

It's the bottom power supply board I'm looking at, p/n EAY41971701.

Just tried it with the set warm and the board cold, but it didn't start up... so inconclusive.

Voltage tests OK at 388v across pins 1 [400v] and 4 [GRD] at connector P601.

[selldoor]

Re: Lg 37LG6000 lcd tv

I think it is on the Main board the one with the inputs near the aerial socket (Tuner box)

[newtothis]

Re: Lg 37LG6000 lcd tv

Freeze spray / canned air is flammable too. I learned that the hard way.

Canned air is better because it's a lot less conductive (but not zero conductivity), it comes out colder and it doesn't stink up the place

Pleas tell the story of the incident! I wanna hear it! LOL

[tom66]

Re: Lg 37LG6000 lcd tv

Uh... if you want. I built a high voltage generator using the flyback from a portable plasma globe (one of these)

Unfortunately back then I had not learned much about snubbing the transformer and was going through MOSFETs every 10 minutes or so. Usually drain-source shorts or drain-gate shorts. I did have nice 4cm arcs in air, about 8kV open circuit. But my FETs (I think they were 100V, 30A devices, so not wimpy!) kept dying and I only had a few left...

To keep the FET cool while doing a test I started freezing it with the canned air... however I forgot about the flammability of the gas, and I had a very active arc nearby... Luckily it only flashed over. No damage to the circuit at all, and even my eyebrows were intact, but the ball of fire was at least 30cm across.

With some later modifications I got 25kV, but that ultimately killed the transformer. Also my arcs were very yellow (high current!) and I was pulling over 30 watts at 12V in so decided it was probably unsafe to go further.

[oddbodd]

Re: Lg 37LG6000 lcd tv

I think it is on the Main board the one with the inputs near the aerial socket (Tuner box)

... and indeed it is.

If this IC is the problem, I don't think I shall be able to replace it... All those tiny solder connections...

Edit: I tried a couple of starts in the warm, and no go.

Meanwhile, I'd found a suitably sized large flat headed bolt in the garage, which I placed in the freezer for about an hour. I then placed the bolt on top of IC404 for a minute or two, to suck the heat out. Powered on, and the set started up.

So it appears that IC404 could well be the culprit.

[T-con]

Re: Lg 37LG6000 lcd tv

If you are an expert in soldering iron you can remove it the hard way (not recommended) but if you have a hot air machine its a piece of cake good luck....