Samsung AV-R720 won't power up properly

[the loner]

I have a Samsung av-r720 that will not turn on properly.
It has stand by power when connected to power, but when I push the power button, I hear a crackling/buzzing noise, or possibly a short in the high voltage transformer, the power light goes blue, but I have no display.
I think the big transformer in the middle of the first picture is the problem.


These are the voltages of the white plug on the left side, plugged in, in standby mode...
Pin 1 -
Pin 2 Gnd
Pin 3-4 .7mv .7mv
Pin 5-6 2.6mv 2.6mv
Pin 7-8 D_Gnd
Pin 9 5.56v
Pin 10 -11.6v
Pin 11 5.63v
Pin 12 U_Gnd
Pin 13 7.24v
Pin 14 0
Pin 15 -40v

These are the voltages of the white plug on the left side, plugged in, powered on...
Pin 1 -
Pin 2 Gnd
Pin 3-4 1.58v 1.58v
Pin 5-6 32mv 32mv
Pin 7-8 D_Gnd
Pin 9 5.6v
Pin 10 -12v
Pin 11 5.63v
Pin 12 U_Gnd
Pin 13 7.12v
Pin 14 0
Pin 15 -41v


The white plug on the bottom, going from right to left (white wire to black) plugged in, in standby mode...

Pin 9 -4.2mv
Pin 8 Gnd
Pin 7 -1.334v
Pin 4-6 0
Pin 1-3 0

The white plug on the bottom, going from right to left (white wire to black) plugged in, turned on...
Pin 9 0
Pin 8 Gnd
Pin 7 -1.334v
Pin 4-6 0
Pin 1-3 0

The third photo looks like some sort of discoloration on the board.
SMR51 looks like possibly a repair. The solder repair on the left side doesn't look right to me.
The last photo looks like another bad solder job on pins 4-5, going from left to right.

I know the voltages are not right but I'm not sure if it's the high voltage transformer.
Any help would be greatly appreciated.

Thanks.

[the loner]

Re: Samsung AV-R720 won't power up properly

Can anyone help me on this one. I don't like playing with high voltage transformers.
If it's not the transformer, then I don't know what it might be.
Also, the power will not shut off when I try to power it off with the power button, I have to actually unplug it to go off.

[the loner]

Re: Samsung AV-R720 won't power up properly

I have the service manual, so I'm going to check out the troubleshooting section.
Maybe I can figure this one out.
I don't have an oscilloscope so I hope that I can do these tests with a digital multi meter.

[the loner]

Re: Samsung AV-R720 won't power up properly

I can't send the service manual, it's too big and I don't know how to zip it smaller, 38mb file

[tom66]

Re: Samsung AV-R720 won't power up properly

I had a friend with a similar model -- bad 470uF 16V capacitor on power supply.

[the loner]

Re: Samsung AV-R720 won't power up properly

I have had time to test some of the caps on the power supply board and they all seem to be within specs. Pictures are below.

I know that the tester that I have is not the greatest, but it gives me some indication of the condition of the caps tested.

I still think that there is something wrong with the high voltage transformer.
The voltages are not right.

[tom66]

Re: Samsung AV-R720 won't power up properly

That CapXon is suspect.

[the loner]

Re: Samsung AV-R720 won't power up properly

tom66, I know that all the caps are crappy on this power supply, but the readings don't look that bad, do they? (I'm no expert, just learning the basics right now, so I'm not disagreeing with you in any way, no disrespect)


How about these pictures. I did not see this before, but I got out my magnifying glass out and I noticed that 1 leg of the transformer is not even soldered to the board. It looks like it has broken off.
The picture is not the greatest, but if you look from left to right, the 3rd hole, the leg is not in the hole, that's why I didn't solder it back. (the other picture has 2 empty holes, no solder)
Maybe, if I put a wire through the hole and somehow solder the wire to the transformer, it may come back.

Good idea or not?

[tom66]

Re: Samsung AV-R720 won't power up properly

That looks normal. The transformer package is a standard shape around which the transformer is built. If that pin is not needed, it won't be connected.

[Pragmatiko]

Re: Samsung AV-R720 won't power up properly

Hello,
attacched you can find schematic diagram and troubleshooting file.
Good work

[the loner]

Re: Samsung AV-R720 won't power up properly

Thanks Pragmatiko. I do have the files that you posted
I have replaced the 3 CapXon caps,(tom66)but it still does not work properly. I have stand by light when plugged in, I have a blue power light when I press the power button, but there is no display and the voltage readings are totally off. (They do not match what was printed on the power supply board)
I still hear that buzzing/popping/crackling sound so I'm going to further troubleshoot this receiver.

[kaboom]

Re: Samsung AV-R720 won't power up properly

Check the heatsinked rectifier to the left of the main TX for shorts.
Also check the non-heatsinked Schottkey and FR diodes for shorts- there are several.


Replace the small cap to the lower right of the main TX- don't waste your time, just replace it. It's in the "aux" supply for the PWM that drives the main TX.

Personally, I'd replace all of those garbage Crapxons. I can't begin to tell you how many power supplies I came across that "weren't quite right" until they were all replaced.

Those "sawblade" caps are suspect, too.

[stevea]

Re: Samsung AV-R720 won't power up properly

Hello All:
I am new to this site and also just got a SAMSUNG AV-R720 given to us by our son who upgraded his surround system, and it just so happens that I have this exact issue, LCD not working, and power button on standby till I turn on the TV, and even with that I cannot turn the unit off till I yank it from the power source.
I will try all the suggestions above to replace the CAPS to see how that helps. Thank you guys, I will post the result here (good or bad)