lg 42lb1dr turning off. (protect mode)

[tucocaps]

Picked up this set a week ago . It's an older LCD with a "built-in" DVR. The guy I got it from said he'd fixed the set once in the past with cap replacement on the power board. Then, problems popped up again, and he says he tried both cap replacement, and a new (refurbished) board. He even gave me the old power board - so i have two of them.

What seems to happen is if the set is started from cold, it will run for up to a minute or so, then shutdown to a red power led. I believe that's "protect mode" according to SM. After that (when warm) it shuts down faster.

Getting confused on this, because it seems the shutdown could be cause by power, main, or signal boards. Found a flowchart in the SM. Have tried to follow it, along with checking supply voltages. Supply voltages look good, except for one 6 volt line (if my eyes are reading right). Also, if "pin 1" on P1064 is the blue wire on the plug, then it is 5 volts high, which i guess would indicated power board problem.

I'm not sure on the check for shorts mentioned in the flow. There are some leads that test positive to ground, but I'm not sure if they are labelled as power leads.

If I can't easily fix , I'd just really like to narrow down to which board is the culprit, or likely culprit.

Thanks for any help on this one!

[tucocaps]

Re: lg 42lb1dr turning off. (protect mode)

When I hold the small reset button on the mainboard, the tv will flash the white power button indefinitely and not shutdown.

[CapLeaker]

Re: lg 42lb1dr turning off. (protect mode)

Do some checks to find out. Disconnect the main board from the PSU and force the PSU on with the backlight connected. See if it still shuts down or not.

[tucocaps]

Re: lg 42lb1dr turning off. (protect mode)

thanks capleaker. not sure how to "force" on the psu.

[budm]

Re: lg 42lb1dr turning off. (protect mode)

The fan assembly looks pretty rusted out, the fan still spinning?. Does the hard drive spin up at all?

[CapLeaker]

Re: lg 42lb1dr turning off. (protect mode)

thanks capleaker. not sure how to "force" on the psu.

I am not either. Can't see the writing on the pin outs. As budm already mentioned, make sure the fan coms on. That thing really looks a bit rusty.

[tucocaps]

Re: lg 42lb1dr turning off. (protect mode)

The fan assembly looks pretty rusted out, the fan still spinning?. Does the hard drive spin up at all?

I actually noticed that, and tried testing the the hard drive completely removed, and that hdd cooling fan unplugged. Made no different, so I'm assuming it's not the fan.

I do see a red led , along with two briefly flashing green led's on the mainboard before shutdown.

[newtothis]

Re: lg 42lb1dr turning off. (protect mode)

But does the fan spin? If the fan is jammed it will protect from overheat (same as if you take the fan out)

[tucocaps]

Re: lg 42lb1dr turning off. (protect mode)

i don't think the fan spins. I wonder if I need to hook up a pc fan or something to test with.

So, you are saying just unplugging the fan may not work?

[tucocaps]

Re: lg 42lb1dr turning off. (protect mode)

I mean the fan will spin with my fingers, but i don't see it turn on.

[newtothis]

Re: lg 42lb1dr turning off. (protect mode)

If the protection system senses that fan simply removing it will trigger it, if the fan is faulty it will trigger it.

[newtothis]

Re: lg 42lb1dr turning off. (protect mode)

Kinda like if a resistor is faulty a system may shut down for protection, removing the resistor alone will not solve it. Only replacing will.

You can briefly try putting load across the fan terminals if it is 2 pin. If it is 3 pin it is sensed

[tucocaps]

Re: lg 42lb1dr turning off. (protect mode)

The fan is a 3 wire. took it out. the rust is really just on the bracket, but the assembly was coated with some sort of goo. Still no go. Not sure if I can replace temporarily with some sort of pc fan, or somehow test this one?

Is there any documentation out there on this mainboard? I notice these two green blinking led's. they start to blink until shutdown.

[tucocaps]

Re: lg 42lb1dr turning off. (protect mode)

http://www.digikey.com/product-detai...399-ND/2560523

this appears to be the fan. has a "locked rotor sensor"

[budm]

Re: lg 42lb1dr turning off. (protect mode)

Normal condition (FAN is spinning) the Blue wire should be LO (<0.5V), it will go HI if it locks up. So look at the Blue wire.
https://cdn.badcaps-static.com/pdfs/...b4ea0682f1.pdf

[tucocaps]

Re: lg 42lb1dr turning off. (protect mode)

Normal condition (FAN is spinning) the Blue wire should be LO (<0.5V), it will go HI if it locks up. So look at the Blue wire.
https://cdn.badcaps-static.com/pdfs/...b4ea0682f1.pdf

Thanks Bud. Actually the wire colors are red/black/yellow, and I assume yellow is the sensor.

I found a computer fan with 3 wires, but I'm not sure the sensor wire is the same.

Also tested the fan, and it does appear faulty. Would not spin with my bench PSU.

The computer fan spun with the TV, but still same shutdown. I'm now wondering if the yellow wire on the computer fan isn't sending the proper -5v signal, if the fan is indeed the problem. Any way I could easily recreate that?

[budm]

Re: lg 42lb1dr turning off. (protect mode)

You need to get the spec sheet of the PC fan since we do not know for sure what the signal pin is. What Voltage do you get at the yellow wire of the old fan, if it is high then you can ground that wire to chassis to fool the sensing circuit.

[tucocaps]

Re: lg 42lb1dr turning off. (protect mode)

woo hoo! thanks a bunch budm. it was just that sensor wire. I had already cut the fan harness in two. just jumped that yellow to gnd, and it ran for several minutes.

i'm thinking that fan wasn't doing much in the way of cooling the hdd on the set anyway. i wonder if it could run without. also not sure if i want to keep this set, sell it, or part out. it's really old, so i'm wondering if the built-in dvr is very useful at all. the set is also EXTREMELY heavy for an lcd. have a sony lcd i saved for my boy, but it has a flaky tcon and may fail again. wonder if i should sell that one and keep this, or the other way around.

oh well , any opinions on this set would be great, now that i got it working with the help of the amazing and legendary BudM

[tucocaps]

Re: lg 42lb1dr turning off. (protect mode)

newtothis, capsleaker: thanks too! i think you guys both had the right idea, and i learned something new about "protection" circuits.

[budm]

Re: lg 42lb1dr turning off. (protect mode)

I would leave the PC fan in it, it will get pretty hot inside otherwise they would have left out the fan and the sensing circuit to save the money.