LG 42in LG 42LM3700 Not powering on

[darkeskye]

I got this tv from a defaulted pawn loan it is a LG 42LM3700 3D Cinema TV. when we took this unit in it was working, not it is not. when PWR button is activated the tv blinks a red LED 3 times and does nothing. I have Taken the back off and searched for bulging caps or burnt components but I've come up empty handed. Here are some pics of what Im working with. Any help is greatly appreciated!

[darkeskye]

Re: LG 42in LG 42LM3700 Not powering on

can i please get some help on this?

[tom66]

Re: LG 42in LG 42LM3700 Not powering on

A good step would be to start making voltage measurements on the top left connector on the power board. There is a legend next to it, which will help you tell what voltages you should expect:
https://www.badcaps.net/forum/attach...6&d=1418611334

[darkeskye]

Re: LG 42in LG 42LM3700 Not powering on

Tom66 I did as you said and tested the pins on the psu board for the inverter and half are labeled 24v and the other half ground and im getting no voltage from any of the pins labeled 24v. So does that mean bad psu board?

[selldoor]

Re: LG 42in LG 42LM3700 Not powering on

Did you test the fuses?

[budm]

Re: LG 42in LG 42LM3700 Not powering on

Tom66 I did as you said and tested the pins on the psu board for the inverter and half are labeled 24v and the other half ground and im getting no voltage from any of the pins labeled 24v. So does that mean bad psu board?

We need the Voltages of each pin on that white connector that goes to the main board (top left of the picture) of the power supply board so we can see which signals are missing, list each pin with its name.
https://www.badcaps.net/forum/attach...6&d=1418611334

[nomoresonys]

Re: LG 42in LG 42LM3700 Not powering on

did you test those 2 fuses?

[nomoresonys]

Re: LG 42in LG 42LM3700 Not powering on

I'm out.

[darkeskye]

Re: LG 42in LG 42LM3700 Not powering on

yes 1st thing i tested were those fuses

[nomoresonys]

Re: LG 42in LG 42LM3700 Not powering on

ok, go ahead and test the fuse on the tcon, it starts with F. http://www.shopjimmy.com/lg-6871l-2981b-t-con-board.htm

[nomoresonys]

Re: LG 42in LG 42LM3700 Not powering on

can see the voltage label/legend better. http://www.shopjimmy.com/lg-eay62769...upply-unit.htm

[nomoresonys]

Re: LG 42in LG 42LM3700 Not powering on

Tom66 I did as you said and tested the pins on the psu board for the inverter and half are labeled 24v and the other half ground and im getting no voltage from any of the pins labeled 24v. So does that mean bad psu board?

now test the voltages on the other connector on the power supply, the label is right there beside it, as always be careful working with power supply, HIGH VOLTAGE, on primary side can be deadly.

[nomoresonys]

Re: LG 42in LG 42LM3700 Not powering on

also try unhook cable from power supply to mainboard, turn tv on see if backlights come on, with your 24volts missing, they prob. wont.

[nomoresonys]

Re: LG 42in LG 42LM3700 Not powering on

not sure, the mainboard may not be sending the ps on signal, which would prob. mean a mainboard issue.

[nomoresonys]

Re: LG 42in LG 42LM3700 Not powering on

need more frequent updates, you got two whole tests done in a month, at this rate you oughta have it fixed by 2020.

[darkeskye]

Re: LG 42in LG 42LM3700 Not powering on

ok well i broke down and bought a mainboard and guess what?.......
problem is still here, my guess is that its a bad psu. now my question is how do i go about trying to repair the psu myself? there is no voltage on labeled pins and no burn components or bulging/leaking caps

[npolite]

Re: LG 42in LG 42LM3700 Not powering on

Hi,

I am having the same problem with this TV as well. Nomoresonys you mention that I should test each pin which is in the upper left two row of pins. When I use my mulimeter I assume that I need to test each one with the positive terminal. Where do I hook up the negative to? Also I see the largest value is 24V. So I just need to set the mulitmeter to something that is above 24V correct?

Thanks,
Nick

[npolite]

Re: LG 42in LG 42LM3700 Not powering on

Here is an update. I was able to find a Youtube video on testing the voltage and found the following:

While off the PWR-ON pin shows 3.5-3.6V. Turning the unit on the PWR-ON pin drops to 0V.
While on I tested a few of the 12V on the left side of the right connector and none of the three showed any voltage. Also the 24V on the left side and right side had no voltage. The only pins that showed any voltage was the four (2 left and 2 right) 3.5V which all showed between 3.5V and 3.6V while the TV was on and off. This appears to be the issue as I assume that the PWR-ON dropping from 3.5V to 0 means that the system is powered on.

If anyone has anything additional to add I would appreciate it, otherwise I'll be ordering a new board off of ebay.

Thanks,
Nick

[npolite]

Re: LG 42in LG 42LM3700 Not powering on

Just wanted to let everyone know that I ordered a replacement power board and that has resolved the issue.

[jakiegu]

Re: LG 42in LG 42LM3700 Not powering on

Just wanted to let everyone know that I ordered a replacement power board and that has resolved the issue.

according all the info showing in this thread, I suggest check following components if you still have that damaged power supply board.

the D605 nearby bridge (+,-,~,~), model number is MUR460AX (4A/600V ultra fast diode). this diode is the key diode between the ac and dc circuit. your voltage lost 24vdc, I believe 12vdc and 3.5vdc lost as well. all the dc voltage is started from this diode.

remove the diode from board and test the bridge first, see if ac 110v-120v in and 170-180vdc send out.

you might can fix that old damaged board by checking this diode.

Good luck.