LG 32LD450 Flashing red light. Inc Schematic

[fruitbat04]

Hi there,

I've got a LG 32LD450. The symptoms are that it's a solid red light when you plug it in. If you hit power, it goes to flashing red, but there's no other activity at all.

I've checked the voltages on the cable from power to main board and they all seem correct although I'm not 100%. If you check this picture



NC is at 0 volts, I assume that means Not Connected though? Power on goes to 3.3 volts which to me seems correct, however is that table indicating to should go to 20v? Doesn't seem right to me.

Heres pictures of the power board and main board. I can't see any signs of any damage or bad caps.





thanks for any help.

[fruitbat04]

Re: LG 32LD450 Flashing red light. Inc Schematic

Sorry, forgot to attached schematic

[fruitbat04]

Re: LG 32LD450 Flashing red light. Inc Schematic

Sorry I wasn't very clear before. With the 20v thing, I meant I was expecting 24v as that is what's on the schematic. As it's generic though, perhaps that's for a different model 37" maybe.

[budm]

Re: LG 32LD450 Flashing red light. Inc Schematic

It is double row pins, so there are two column, left column and the right column, for example: the left column bottom pin is the pwr pin, the pin above it is the 20Vdc output pin, the right column bottom pin is 20VDC. So the board does send out the POWER ON (PS_ON), how about the voltages of other pins?
Also check the DC Voltage (when TV is OFF and when TV is ON) right at the two legs of the two main filter caps (450vdc rating) laying on the side?

[fruitbat04]

Re: LG 32LD450 Flashing red light. Inc Schematic

Yeah sorry, I got it was a double set of pins, was just really unclear in the first post! All pins both sides seem ok. I'm not sure what error is supposed to be but it's about 0.9v. Power on does send out 3.3v when you hit standby and all the pins that should go to 12v/20v.

However the main filter caps are 170v on standby and about 230v on power. That's assuming you mean to chassis ground and by right leg you mean the positive one.

[fruitbat04]

Re: LG 32LD450 Flashing red light. Inc Schematic

interestingly, when you switch it off at the mains, they jump to about 330v and stand to come down.

[fruitbat04]

Re: LG 32LD450 Flashing red light. Inc Schematic

Oh if you mean the across the legs of the caps, they go from 320 to 390.

[budm]

Re: LG 32LD450 Flashing red light. Inc Schematic

"However the main filter caps are 170VDC on standby and about 230v on power" That does not look right since you are in UK, I expect to see around 330VDC right at the two legs of the cap when TV is OFF, then it should jump up to around 360~400VDC when the PFC Voltage kick on when it receives the power on signal.

[fruitbat04]

Re: LG 32LD450 Flashing red light. Inc Schematic

Yeah, sorry I didn't realise you meant across the legs. That's about bang on what I get.

[budm]

Re: LG 32LD450 Flashing red light. Inc Schematic

That is goods, it means the PFC is working. So for the backlights to come on, you will need that INV ON/OFF signal from the main board feeding that INV ON/OFF pin. What do you get at that pin when TV is OFF and when TV is ON (black probe of the meter on the chassis)?

[fruitbat04]

Re: LG 32LD450 Flashing red light. Inc Schematic

Not much! 0v on standby and 37mv on power.

[fruitbat04]

Re: LG 32LD450 Flashing red light. Inc Schematic

If I short PWR ON to INV ON, the backlight comes on, still doesn't boot though.

[budm]

Re: LG 32LD450 Flashing red light. Inc Schematic

Well, that means at this point the problem is in the main board. I would do real close up inspection on both sides of the main board and then check the voltage of the voltage regulator ICs.

[fruitbat04]

Re: LG 32LD450 Flashing red light. Inc Schematic

Thanks very much for your help. I've got a pretty decent USB microscope so will get it under that tomorrow and report back.

I've found a replacement board on ebay for £29 which isn't too bad, I'd like to fix it at component level, if possible though!

[budm]

Re: LG 32LD450 Flashing red light. Inc Schematic

I myself never really fix anything more than just bad regulators or bad caps on the main board.

[fruitbat04]

Re: LG 32LD450 Flashing red light. Inc Schematic

Had a look round and still can't see any damage. The voltage IC's seem ok in that they are showing things like 3.3v, 2.5v etc but I'm not sure exactly how to check them more scientifically.

The main processor is getting pretty hot, nothing else though.

Is it time to just bite the bullet and get a new board?

[fruitbat04]

Re: LG 32LD450 Flashing red light. Inc Schematic

I got a replacement board but it's the exact same problem.

Any other ideas?

thanks

[budm]

Re: LG 32LD450 Flashing red light. Inc Schematic

I got a replacement board but it's the exact same problem.

Any other ideas?

thanks

So are you still getting the PS_ON, and still get 370VDC on the main filter cap? We need to find out if all the signals we tested on the old board are still the same as the new board or not.

[fruitbat04]

Re: LG 32LD450 Flashing red light. Inc Schematic

I'll check when I'm back home.

One thing I did wonder is the inverter board seems to be part of the power board on this model as the backlight is fed directly from the power board. The other couple of TV's I've done all have them as a separate board. Could this have a bearing on that INV_ON pin which doesn't seem the be getting triggered?

[fruitbat04]

Re: LG 32LD450 Flashing red light. Inc Schematic

On the new one, I seem to get the 3.3v standby, but none of the other voltages when I hit power (still get the red flash though). If I jump the PWR_ON, the voltages come up, but the TV still doesn't turn on.