Samsung LN-T665F

[heavymachines]

OK, have this 46" sammy with power supply issue. It has 5v stby and has 2.7 coming from main to tell it to turn on. the main tries then gives up and try again as repeating cycle. the power supply has no other voltages or so low it's not even worth writing down on cn801, no voltages on cni 805 and nothing on cni806, this power supply is very similar to the recent samsung i repaired on this forum. Now i can replace it for 40 bus but if i can fix it for less why not.

[dskall]

Re: Samsung LN-T665F

You've forced it on and no voltages. Pfc voltage?

[dick_barton]

Re: Samsung LN-T665F

Is this the schematic?

https://www.electronica-pt.com/esque...-00167a-17741/

[heavymachines]

Re: Samsung LN-T665F

You've forced it on and no voltages. Pfc voltage?

No boosted voltage, matter of fact over half the board checking around has very unstable voltages and doesn't climb very high at all. So something is loading it down. Still checking will add details.

[heavymachines]

Re: Samsung LN-T665F

Is this the schematic?

https://www.electronica-pt.com/esque...-00167a-17741/

Close, looks little diffrent board number is BN44-00166B. it might be close enough will check it over more.

[budm]

Re: Samsung LN-T665F

The standby Voltage is steady, right? If it is cycling on and off due to PS-ON is cycling on and off then the rest of the switched power supplies and the PFC will not be stable.
It is best to forced on the board by itself to see what you will get.
BN44-00166C schematic may be close enough to revision B.

Pictures of BN44-00166B are provided by shopjimmy.

[heavymachines]

Re: Samsung LN-T665F

Will double check in morning, I am certain if my memory serves me right stby was stable and turn on 2.7 was not it would hold at 2.7 for approx 3-5 seconds and go down then back up in intervals as if it is trying like hell to start the tv no other voltages worth mentioning would come up or very low and unstable. I did try forcing on with resister with same results BUT i will do the test again to be sure first thing.

[heavymachines]

Re: Samsung LN-T665F

Ok stby is stable at 5.16 volts for some darn reason been unsuccessful to get the relay to latch jumping w/resistor, main diconnected but the bugger will latch with main connected however like i said the 2.7v ps/on will engage for 3 to 5 seconds then give up and reengage in a endless cycle.

[dskall]

Re: Samsung LN-T665F

What voltage you get on ps-on. Maybe resistor is dropping votage to much

[heavymachines]

Re: Samsung LN-T665F

What voltage you get on ps-on. Maybe resistor is dropping votage to much

2.7v ps on

[budm]

Re: Samsung LN-T665F

Forcing on the board with resistor and gets 2.7VDC, that should more than enough to bias on the main power relay driver QB801, and PS-ON switched Transistor QB854 based on rev C diagram, unless there are problem with OPTO PC802S, QB812, 813, ZB803. So you need to check those Voltages in that path which supplies the switched VCC.
BTW: There will be no 5.4VDC for the relay coil until PS-ON circuit is working to supply the switched VCC

[heavymachines]

Re: Samsung LN-T665F

Forcing on the board with resistor and gets 2.7VDC, that should more than enough to bias on the main power relay driver QB801, and PS-ON switched Transistor QB854 based on rev C diagram, unless there are problem with OPTO PC802S, QB812, 813, ZB803. So you need to check those Voltages in that path which supplies the switched VCC.
BTW: There will be no 5.4VDC for the relay coil until PS-ON circuit is working to supply the switched VCC

Ok think maybe little confusion here on my part and others. Here is what i did, it only gets 2.7v from main to power supply but is only holding for 4 or 5 seconds and it goes down then it tries again for another 4-5 seconds in endless loop.

Standby volt is stable regardless if main is connected or not.

Relay only clicks when main connected.

With main disconnected the power supply only has standby 5.16 volts to use to jump to ps/on no other voltages to use and no clicks nothing and i am stumped as to why. Maybe you can clear this up for me. maybe need more resistance with a bigger resister?

[budm]

Re: Samsung LN-T665F

You need to check the Voltages in that switched VCC path as described in my post #11 when you are forcing on the power supply board.
What DC V do you have on that PS-ON pin when you run the power supply board by itself and PS-ON pin is connected to the 5.1V stby pin using the 470~1000 Ohms resistor?
Since the relay did at least click when connected to the main board, so if using the resistor to force on but you do not hear the relay clicks then something is not done right some where.
At this point I suspect the problem in the main board due to PS-ON is not stable.

[heavymachines]

Re: Samsung LN-T665F

I was only using a 75ohm resister will use a bigger one see if we can get the relay to latch. Worked before in forced ps on on other tv's before. Only thing i can think of is need more resistance.

I would be more convinced main is the problem if i can get the relay to latch and get rest of the voltages to come up on power supply without the main connected is that a reasonable assumption?


Have no idea what else i could be doing wrong it really simple to jump standby to ps_on with resister but it won't latch. Not enough voltage drop? in my mind one would think it would still latch just latch harder? Not sure but i am sure you know why?

[heavymachines]

Re: Samsung LN-T665F

Heck if my new screen comes in on time for my phone tomorrow. i'll upload a video showing me doing the jump and show it refuses to latch, will especially do this if it still won't latch with bigger resistor.

[budm]

Re: Samsung LN-T665F

The main point is that we need to know what DCV you have at the PS-ON pin when you use the resistor.
More resistance = less current to bias on the Transistor.
We know that when you have main board connected to the power supply board, you get 2.7VDC which is enough to turn on the power supply and the relay, but the PS-ON output of that main board is not holding steady high state but it goes down and come back up, so when it goes down the switched power supply is turned off so the relay also drops out and then the PS-ON goes high again then switched power supply comes back on so as the relay.
When you are using the resistor, you are just simulating the steady PS-ON signal, that is, nothing special.

[heavymachines]

Re: Samsung LN-T665F

The main point is that we need to know what DCV you have at the PS-ON pin when you use the resistor.
More resistance = less current to bias on the Transistor.

Will do first chance.

[dskall]

Re: Samsung LN-T665F

Just need to know when you force on voltage is at least 2.7dcv

[budm]

Re: Samsung LN-T665F

With only 75 Ohms resistor, it should be a lot more than 2.7V.

[dick_barton]

Re: Samsung LN-T665F

You need the 5.4V to supply power to the relay coil and when PSON is connected to STBY (5.2V) it should bring the relay on.