50UH5500 No picture/sound

[lfhlaw]

So I picked up this 50UH5500 the other day.

When I power it up, the main board gets power for brief second, the backlights flash and then power shuts down to the Backlights and Main.

Testing the PSU-
With the Power plugged in
Power
pin 1- STB - 0 V
pin 2,3 - 0 V
Pin 4,5,6,7,8 - get 10.22 V
pins 9,10,11,12 - 0 Volts

where the LED plug is.
pins 1,2,3 - 88-89 Volts
pins 4,6 give 27-28 volts.
pin 5 - 0 Volts

Based on the LED pin voltages, I'm assuming i have a bad LED. However the weird thing that gets me is the STB being 0 V. I always thought they were supposed to be about 3.5 V.

Reading at ShopJimmy...that these TV's also really had a tendency to have LED Failure as well.

[Davi.p]

Re: 50UH5500 No picture/sound

First check the power board by itself, so get a car light bulb or a ceiling headlight with 12v 50w and put it on the 13v/0v outputs, if it light up well and steady P.B. is ok. It's impossible that mainboard did get power for some seconds 'cause PSU is always on. The STB=standby signal is only from m.b. to p.b to switch on the PFC. So i guess you have a mainboard problem. It is almost sure because PSU have no error signal that can switch off some tensions on the m.b. in a standby state. You can have a standby software messed up or a short circuit on a regulation stage or a mpu or cpu. etc..

[lfhlaw]

Re: 50UH5500 No picture/sound

First check the power board by itself, so get a car light bulb or a ceiling headlight with 12v 50w and put it on the 13v/0v outputs, if it light up well and steady P.B. is ok.

ok I can get a car light bulb, but not sure what you mean by put it on the 13v/0v outputs - the outputs on the power connector and just physically place it against the pins? Or should I purchase a few connector wires or such?

[budm]

Re: 50UH5500 No picture/sound

Pin 1 STB = PS-ON
Pin 11 ENA = BL-ON
Pin 12 ADJ = Backlights dimmings

So the main board is not sending the control signals to the power supply board.

[Davi.p]

Re: 50UH5500 No picture/sound

I mean only that a bulb need two poles connected, 13v and 0v.. Check well the tension under load because that 10v is not OK..
sorry i change my diagnosis, i haven't noticed well the 10v, i thought you had low bat on tester, but seems not ok the PSU that outputs a little current then goes into protection. If the test fails post a picture of the underside of the psu. I correct myself, the PFC can't be activated by STB 'cause there's 1 only opto. I don't figure out to understand what STB does..

[lfhlaw]

Re: 50UH5500 No picture/sound

Turned out that it was a bad LED strip.