39LN5300 with black screen, no image with flashlight
I have a LG 39LN5300, manufactured 2/2014, with a black screen, but with sound (static). I looked at trouble shooting guides and confirmed there is no image even with a flashlight. I replaced the motherboard but this did not solve the problem. Now I am suspcious of the power supply board, but would like to verify if mine is bad first. I am able to use a volt meter.
I took meter readings from the P201 9-pin plug for ribbon cable to motherboard. Next to the plug there is a chart with 2 columns of 8 numbers each:
Left column says "PWR-ON", lists bottom to top:
3.5, 3.5, GND, 24v, GND, 12V, 12V, GND
Right column says "DRV-ON", lists bottom to top:
PDIM, N.C., GND, 24V, GND, 12V, N.C., GND
Readings from bottom to top as follows:
a. Plugged in but not turned on: 0, 3.3, 3.3, 0, 0, 0, 0, 0, 0
b. Plugged in, turned on with remote: 3.0, 3.2, 3.2 0. 23.8, 0, 12, 12, 0
Can one tell from these readings if my power supply is bad?
Thanks.
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2 commentaires
If no answer forthcoming here you might want to check out:
https://old.reddit.com/r/TVRepair/
par prop man
I see P201 above is an 18-pin plug.
Note the following per the trouble shooting flow chart link:
1) “Check stand-by Voltage. P401 3, 5pin : +3.5V_ST. “ P401 is on the motherboard and receives the cable from P201 on the power board. I have 3.38 volts on pin 3, i have zero on pin 5. SO I am not getting standby voltage.
2)The next step if I don't have the 3.5 v is "Check 18pin Power connector". i unplugged and re-plugged both ends, and it doesn't exhibit any damage. I could try to check continuity across all 18 pins but it seems unlikely to me that the connector or plugs went bad. BUT….i did have 3.38 v out of two pins at P201. Thoughts?
3) If OK, the next step is "Main B/D 3.5V Line Short Check" . Not sure how to do that: I am not sure where the 3.5 v line is, nor how to check it for shorts. Suggestions?
4) If it is OK it says "Replace Power Board."
I am thinking that it is worth the gamble that the power board is bad, but would love to be able to do steps 2 and 3 if anyone can guide me.
par Robert Allen