Samsung le40a656a1f reaaaaaly slow poer up

[kavleas]

Re: Samsung le40a656a1f reaaaaaly slow poer up

Funny, voltage reached 11.5 volts and when connected to load (car bulb 60w) it dropped to 5 volts and the backlighting was flashing on and off!

[Davi.p]

Re: Samsung le40a656a1f reaaaaaly slow poer up

replace the shunt regulator for feedback, like tl431 or similar

[lotas]

Re: Samsung le40a656a1f reaaaaaly slow poer up

You all changed the electrolytic capacitors in the power supply, how is the PFC (Power Factor Corrector), what is the voltage on the large capacitor in standby mode and in operation?

[kavleas]

Re: Samsung le40a656a1f reaaaaaly slow poer up

You all changed the electrolytic capacitors in the power supply, how is the PFC (Power Factor Corrector), what is the voltage on the large capacitor in standby mode and in operation?

Standby:315V, Power on:380V

[kavleas]

Re: Samsung le40a656a1f reaaaaaly slow poer up

replace the shunt regulator for feedback, like tl431 or similar

Removed 431 (ICM803) and it measures ok. What I still don't understand is what happened when heating the electrolytics and the voltage rose!

[lotas]

Re: Samsung le40a656a1f reaaaaaly slow poer up

Removed 431 (ICM803) and it measures ok. What I still don't understand is what happened when heating the electrolytics and the voltage rose!

It is necessary to replace all electrolytes with new ones.

[Davi.p]

Re: Samsung le40a656a1f reaaaaaly slow poer up

Already done Lotas..
to the OP, you can't measure a TL431, it's not a transistor, you better change it.. to be sure grab one from a working ps just to test purpose, this because there are probably fakes on the market..

[kavleas]

Re: Samsung le40a656a1f reaaaaaly slow poer up

Already done Lotas..
to the OP, you can't measure a TL431, it's not a transistor, you better change it.. to be sure grab one from a working ps just to test purpose, this because there are probably fakes on the market..

Unfortunately I can't seem to find a 431 to replace the existing one but it's a zener diode and it measures ok. Voltage accross led part of optocoupler PCM801 is 1v.

[Davi.p]

Re: Samsung le40a656a1f reaaaaaly slow poer up

it's not a zener diode you can't measure it..

[lotas]

Re: Samsung le40a656a1f reaaaaaly slow poer up

The TL431 chip is an adjustable zener diode. It is used as a reference voltage source in the circuits of various power supplies.

[kavleas]

Re: Samsung le40a656a1f reaaaaaly slow poer up

I get a bizarre reading when connecting ammeter between psu and mb on the 5v stand by rail. It indicates 0.5A. This doesn't seem normal (tv is turned off). Is there a schematic of the mb (BN41-00974B)?

[lotas]

Re: Samsung le40a656a1f reaaaaaly slow poer up

Is there a schematic of the mb (BN41-00974B)?

Service Manual BN41-00974B

[kavleas]

Re: Samsung le40a656a1f reaaaaaly slow poer up

Wow THAT was fast, thanks!

[Davi.p]

Re: Samsung le40a656a1f reaaaaaly slow poer up

In post #41 you told the psb behaves bad also whithout the main board, so it is not important to jump to the mainboard attention.. how many tl431 are there? The one to be changed must be the one of the 13v supply stage

[kavleas]

Re: Samsung le40a656a1f reaaaaaly slow poer up

I thought to check if something is shorted on the mb and affects the psu. I see 4 431s on power supply, I checked the feedback one. Will check the rest and try to find replacements.

[Davi.p]

Re: Samsung le40a656a1f reaaaaaly slow poer up

You can't check a main board without a good power supply

[kavleas]

Re: Samsung le40a656a1f reaaaaaly slow poer up

There is the culprit for the high current on the 5v stand by voltage! The diode and the cap are shorted. Trying to find a way to turn on the set without the panel (led,touch,infrared) connector.

[Davi.p]

Re: Samsung le40a656a1f reaaaaaly slow poer up

pullup the ps on line..

[nomoresonys]

Re: Samsung le40a656a1f reaaaaaly slow poer up

If you didn't yet, unhook that board from both sides and retest the diode and cap, if they both still read short, take out of circuit the easiest one to get out first and recheck and check where they connect to the board see if the short is still there or gone, need to fix any short or tv won't work.

[kavleas]

Re: Samsung le40a656a1f reaaaaaly slow poer up

I removed the grey ribbon (touch pcb) from the small pcb and the short is gone. Powering on, the cap voltage is 5 volts, ir still works but once again no image or sound. Going to remove the diode and see...