Sony Bravia KDL-46EX621 won't power on

[gijoey198079]

Picked this up just a bit ago, got it home and plugged in and instantly turned on. Picture and sound was working good for about 1 minute then it shut off.

The previous owner said it just radomly shut off but has recently started doing it alot more often.

It did this to me 3-4 times and now it won't power on. I plug it in and get a standby light, when I press power the light goes off but you can hear the transformers humming. Looks like 1-2 caps may be bulging but not 100% sure as I don't have an ESR to check.

At no time has it blinked any error codes. Could the caps have caused the random shut offs and they finally went bad and now won't work?

[gijoey198079]

Re: Sony Bravia KDL-46EX621 won't power on

Correction, I left it plugged in for a bit and now it is blinking red led 8 times.

[budm]

Re: Sony Bravia KDL-46EX621 won't power on

Can we see the pictures of the boards, caps? Unstable DC can cause random problems.

[gijoey198079]

Re: Sony Bravia KDL-46EX621 won't power on

Charging camera now, the caps are very small and long on this one and its hard to tell for sure if they are bulging but I think 2 of the 4 are. I just tested output from power supply, all seems good except all the 12v going to the t-con is only putting out 11.80 - 11.85v.

I'm thinking this could be too low and caused by the caps maybe?

It will now come on and stay on for about 1 minute, then powers off and right back on and repeats this cycle 4 times then shuts off and led light blinks 8 times. At this point you have to unplug power cord wait then plug back in to power on tv.

[budm]

Re: Sony Bravia KDL-46EX621 won't power on

11.80~11.85 is fine for for the T-CON.

[gijoey198079]

Re: Sony Bravia KDL-46EX621 won't power on

I rechecked and looks like all the 12v outputs are between 11.80 - 11.90.

I pulled one of the caps up to try and get a pic of the bulging but can barely see it still, think the one on the other end maybe bad as well.

[budm]

Re: Sony Bravia KDL-46EX621 won't power on

OK, you have TV with LED backlights. This power supply board has PFC Voltage booster circuits, so the voltages on those 4 caps when the TV is off should be around 170VDC (measure at the legs of the caps, the negative legs of these caps are the primary ground ref. point for the primary circuit so be careful not to touch any part of this circuit in that areas), when you hit the power switch, the board will get the PS_ON SIGNAL from the main board to turn on the power supply which will cause the PFC circuits to start up and charge up those 4 caps to about 380~400VDC. We need to find out what the 8-blink code is for this TV.
If those caps lost their capacitance, the PFC choke will be buzzing, so do not keep running it otherwise it may damaged lots of circuit. If the tops of the caps had any dome at all, I would replace all 4 of them.

[gijoey198079]

Re: Sony Bravia KDL-46EX621 won't power on

Replaced all 4 capacitors this morning no change. I get a buzzing from the t-con but no where else other than a very faint buzz from the transformers.

Also I have tried to run a firmware upgrade but it won't stay on long enough to start it.

[ben7]

Re: Sony Bravia KDL-46EX621 won't power on

Replaced all 4 capacitors this morning no change. I get a buzzing from the t-con but no where else other than a very faint buzz from the transformers.

Also I have tried to run a firmware upgrade but it won't stay on long enough to start it.

Have you checked the other voltage outputs from the PSU (if it has them)?

[gijoey198079]

Re: Sony Bravia KDL-46EX621 won't power on

I found that the main board is sending the signal to shut off the set then turn back on, looks like I'm gonna need a new main board.

[gijoey198079]

Re: Sony Bravia KDL-46EX621 won't power on

Got a question, went to order a motherboard, found 1 but my part number on my board here is A1814571B the ones I have found are A1814572B. I am seeing that these are possibly either the same board or at least compatible, anyone know for sure?

[gijoey198079]

Re: Sony Bravia KDL-46EX621 won't power on

Sorry to bump but someone here must know if these 2 boards are compatible or not, please...?