Samsung D580 LCD TV - No Power

[mikay786]

Hi guys, picked this up this morning as spares / repair job, and it has no power what so ever. No standby.

Checked all fuses which are good.

So starting off on power supply, caps look ok but will test shortly. I'm thinking issue may be with bridge rectifier.

I have tested it in circuit and the 2 middle pins seems to be passing current both ways on multi meter in diode mode. The +/- seem ok as they only work one way but the two centre pins seems to be shorted.

Is it ok to test this in circuit or should I remove and test again?

Anything else I should check out?

[mikay786]

Re: Samsung D580 LCD TV - No Power

So pulled it out and above was wrong, I had it on wrong mode but reading it now it only goes one way but

positive probe to - on bridge rectifier

- to ac = 0.47
- to ac (next pin) = 0.47
- to + = 0.86

is the - to + @ 0.86 too high?

[Moreno83]

Re: Samsung D580 LCD TV - No Power

So its completely dead? No 5V standby on pin12?

You need to measure the voltages on the PSU from the outlet untill it stops.
I think its a mainboard problem , do you know any history of the tv?

[mikay786]

Re: Samsung D580 LCD TV - No Power

Don't know history, guy just said it had no power. Ive put the bridge rectifier back in and will now check if it has 5v on pin 12 (which I probably should have done first!!)

[mikay786]

Re: Samsung D580 LCD TV - No Power

No 5v on the connector on the left of the board, unplgged the cable at the main board side and measured on the connector itself. In fact none of the pins seems to have any current in them. (so no 5v coming out of the psu board)

Ive measured 330v dc on the main caps

[Moreno83]

Re: Samsung D580 LCD TV - No Power

Whats the type of the tv? For example : LE32D580K2K
Maybe we can find a service manual for this tv.

So you measure some voltages on the hot ( high voltage ) side of the board. Is it the picture or is one of the mosfets on the left of the big blue caps damaged on top?

[Moreno83]

Re: Samsung D580 LCD TV - No Power

The fet next to the fuse

[mikay786]

Re: Samsung D580 LCD TV - No Power

LE40D580k

Might just be picture, heres a couple more

[Moreno83]

Re: Samsung D580 LCD TV - No Power

Do you measure any voltages on the cold side of the board? Hot is the area with the big caps and there is a white line. Any voltages on the transformer?

[Moreno83]

Re: Samsung D580 LCD TV - No Power

Btw , if you unplug the mainboard. Do you get 5v back?

[mikay786]

Re: Samsung D580 LCD TV - No Power

ill have to check, just checking the caps and they all seem fine. Testing the transistor next to the caps.

One thing, but perhaps I'm doing some wrong, was the fuse on the left has 330v dc going through it. But the fuse on the right near the power plug has no reading at all on ac or dc?

But how could the rest of the board be receiving power if that's reading 0?

[mikay786]

Re: Samsung D580 LCD TV - No Power

Main board was unplugged, no 5v coming out of the PSU board.

[Moreno83]

Re: Samsung D580 LCD TV - No Power

Are you sure? Black lead on ground and red on the fuse , you dont measure anything?

[mikay786]

Re: Samsung D580 LCD TV - No Power

my bad I was putting both probes on it, checked again with ground

104v ac only (surely this should be 240v for uk?)

and only 8v dc on the other

[mikay786]

Re: Samsung D580 LCD TV - No Power

its not a US model as on the label on back of tv says 220-240v

[budm]

Re: Samsung D580 LCD TV - No Power

my bad I was putting both probes on it, checked again with ground

104v ac only (surely this should be 240v for uk?)

and only 8v dc on the other

1) When you make the ac AC Voltage measurement in the primary side for the incoming AC you measure between Line and Neutral, not to GND.
2) When you make the measurement in the DC circuit in the primary (HOT side) side, you will use the Negative leg of the main filter cap as the GND ref for the meter.
3) When make the measurement int he secondary side (COLD side), you can use the chassis as the GND ref. for the meter as long as the board is still mounted to the chassis.

So what DCV do you have when you measure it between the two legs of the main filter cap?

[mikay786]

Re: Samsung D580 LCD TV - No Power

even weirder when I reverse the power cable it goes up to 130v, and if I flip it measures 104v. Just a regular figure 8 power cable. Tried a different one and same thing

[budm]

Re: Samsung D580 LCD TV - No Power

even weirder when I reverse the power cable it goes up to 130v, and if I flip it measures 104v. Just a regular figure 8 power cable. Tried a different one and same thing

Please read post 16, you are not measuring it correctly.

[mikay786]

Re: Samsung D580 LCD TV - No Power

1) When you make the ac AC Voltage measurement in the primary side for the incoming AC you measure between Line and Neutral, not to GND.
2) When you make the measurement in the DC circuit in the primary (HOT side) side, you will use the Negative leg of the main filter cap as the GND ref for the meter.
3) When make the measurement int he secondary side (COLD side), you can use the chassis as the GND ref. for the meter as long as the board is still mounted to the chassis.

So what DCV do you have when you measure it between the two legs of the main filter cap?

330v dc between main caps (probe on each leg)

[mikay786]

Re: Samsung D580 LCD TV - No Power

Please read post 16, you are not measuring it correctly.

ah ok understood