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**ngth82** · 04-04-2020, 10:12 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

Can you post a picture of the backside of the power board?
Identify the two and three legged TO-220 package parts (the ones that are heatsinked), and measure them for shorts on diodes, or on the FETs. If you don't know how to do this, google is your friend.
Look at the four rectifier diodes on this board. (D750, D751, D752 and D753). If you have the ability to do so, unsolder one at a time and test it in diode mode with your meter. (Be sure to note the orientation when you install it.!!!)
Are there any noticeably darker areas on the back of the power board?
What is the voltage on the big main cap (C800A)?

Edit:
- Try disconnecting the power cable between the SMPS (power board) and the main board. Do the supplies come up? Does it buzz? Does it sound normal?
- If the supplies don't automatically enable, use a 10kOhm resistor between STBY3.3 and POWER_ON to force the SMPS on.

**heathloder** · 04-05-2020, 10:14 AM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

Thanks for the response!

Are there any noticeably darker areas on the back of the power board?

I've attached photos of the back of the SMPS board, which does not *appear* to be damaged.

Identify the two and three legged TO-220 package parts (the ones that are heatsinked), and measure them for shorts on diodes, or on the FETs. If you don't know how to do this, google is your friend.

Do I need to actually remove the FETs to test them? Does this mean that I need to remove the heatsinks too? I've found TO-220 testing procedures through Google, but I was really hoping to not have to remove the heatsinks...

Look at the four rectifier diodes on this board. (D750, D751, D752 and D753). If you have the ability to do so, unsolder one at a time and test it in diode mode with your meter. (Be sure to note the orientation when you install it.!!!)

I will attempt to try this today, and get back to you with my results ASAP.

What is the voltage on the big main cap (C800A)?

Are you asking what it operates at, or what it's rated at? C800A is rated at 570V, 120uF, but I haven't tested it while the system attempts to power on.

- Try disconnecting the power cable between the SMPS (power board) and the main board. Do the supplies come up? Does it buzz? Does it sound normal?

If the cable between the SMPS and mainboard is unplugged, there is no way to trigger power on (without the use of the resistor and STBY voltage), so nothing happens at all in this state.

- If the supplies don't automatically enable, use a 10kOhm resistor between STBY3.3 and POWER_ON to force the SMPS on.

Unfortunately, I don't have any resistors immediately available to me, so I am going to order some today and I will do this test when they arrive. I do have some 1N914 diodes sitting around - I wouldn't be able to use one of those in place of a 10k ohm resistor, could I?

Thanks again for your help!

Attached Files

**heathloder** · 04-05-2020, 10:23 AM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

Quick update:

As I was about to attempt to remove the rectifier diodes you mentioned (D750, D751, D752, D753), I noticed some discoloration on D752 (marked in the attached photo).

I still need to remove them and test them, but I thought this might be pertinent information worth sharing.

Attached Files

**nomoresonys** · 04-05-2020, 12:25 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

A quick test is test them in diode mode, should probably get .2xx to about .7xx in one direction, switch probes and get OL or 1 in other direction, any that are suspect should lift a leg and test again out of circuit.

**R_J** · 04-05-2020, 01:18 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

Pin 3 (CN6802-1) -OUT1-1 = Jumps between -60mV - +60mV (rises to +60mV when buzzing)
Pin 4 (CN6802-2) -OUT1-2 = Jumps between -60mV - +20mV (rises to +20mV when buzzing)
Pin 5 (CN6802-3) -OUT2-1 = Jumps between -60mV - +30mV (rises to +30mV when buzzing)
Pin 6 (CN6802-4) -OUT3-1 = Jumps between -60mV - +40mV (rises to +40mV when buzzing)
Pin 7 (CN6802-5) -OUT4-1 = Jumps between -75mV - +5mV (rises to +5mV when buzzing) <--- this is likely the bad led string
Pin 8 (CN6802-6) -OUT4-2 = Jumps between -80mV - +100mV (rises to +100mV when buzzing)
There are 6 strings, each string has 3 strips with a total of 27 led's (27*3v each=81v) There are a total of 18 seperate strips in the panel (3 strips per string)

**brucetv** · 04-05-2020, 02:04 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

We had two of these in last month. Same pulsating buzz. Check D751A and Q750A on power supply and if they are fine replace those four rectifier diodes. I believe they are 5A 150V Schottky. Or you can get the power supply from www.tvpartstoday.com for about $65 plus shipping

**brucetv** · 04-05-2020, 02:46 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

R J
When you had those voltages on C6802 did the Tv give you any error blink code? I believe this model uses a bottom edge lit bar. We did one about 6 months ago. No error blink code but we did find one led shorted. We got luckier with the other two with diode replacement.

**heathloder** · 04-05-2020, 03:55 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

Thanks for all of the responses. I ordered some 10k ohm resistors.

I still haven't removed the rectifier diodes, but I did try to test them, in diode mode, while in-circuit:

D750: Rev: OL, Forw: .289V
D751: Rev: OL, Forw: .289V
D752: Rev: 0V, Forw: 0V
D753: Rev: 0V, Forw: 0V

I'm not doubting you could be correct RJ, but when I took those readings, they were all over the place (inconsistent) for all of those pins: the voltage on every pin spiked when the transformer buzzed, but the voltage level on all pins would vary during each spike. The "strength" of the buzzing noise corresponded to the voltage reading I'd get on my multimeter, which fluctuated "randomly". The power supply behaves this same way with the LED strings unplugged, as well.

I will check D751A and Q750A as soon as possible and get back to you with what I find out.

brucetv, those readings that RJ posted were just mine from my original post - it's possible that is simply a bad reading. I could easily try it out again and get back to you, but the readings are hard to take because I only have a digital meter and the spike occurs so quickly. I have no LED's/lights on the bottom bar where it normally would appear. The edge-lit bar you described is there, but it's not illuminating.

Thanks again for all the help.

**R_J** · 04-05-2020, 03:57 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

Originally posted by brucetv View Post

R J
When you had those voltages on C6802 did the Tv give you any error blink code? I believe this model uses a bottom edge lit bar. We did one about 6 months ago. No error blink code but we did find one led shorted. We got luckier with the other two with diode replacement.

These are not my voltages, they are the OP from post#1

You may want to check the voltage across the main filter C800, to see if the pfc circuit is working. You should have around 160v in standby and 380v when power on.

Also what is the voltage rating on C753A or C756A? The board lists the led voltage at 163v

**heathloder** · 04-05-2020, 05:41 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

Still haven't gotten around to removing any components...

You may want to check the voltage across the main filter C800, to see if the pfc circuit is working. You should have around 160v in standby and 380v when power on.

Just checked this - getting 393V while buzzing, and drops to about 382V between buzzes, and then ultimately drops to 163V after 7 pulses and going quiet (I assume it's going into standby at this point).

Also what is the voltage rating on C753A or C756A? The board lists the led voltage at 163v

Voltage rating on these are 200V 33uF, but I didn't actually measure the voltage across them.

I'm going to attempt to remove D751A and Q750A next so that I can check them.

**nomoresonys** · 04-05-2020, 05:57 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

D752: Rev: 0V, Forw: 0V
D753: Rev: 0V, Forw: 0V
Maybe lift a leg and recheck.

**R_J** · 04-05-2020, 06:13 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

It could be that D752/D753 are bad, or you are also measuring the transformer winding. In post #6 I was looking at the wrong led's at SJ, This model must be edge-lit so when I counted the led's I made a mistake.

**heathloder** · 04-05-2020, 07:03 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

I lifted one leg of D752 (photo attached because I've never done this before and just want to make sure I'm doing it as you're expecting). That was not easy to get that leg up...

Now, when I test D752, I get 0V both ways, and when I test D753, I get .310V forward, and OL reverse. The results for D750/D751 didn't change.

Does this mean that D752 is bad? I am still planning to test D751A and Q750A. I'll post those results once I finally get around to it :p (hopefully later tonight or tomorrow).

Attached Files

**budm** · 04-05-2020, 07:31 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

D752 is bad since it shows conduction on both directions.

**heathloder** · 04-05-2020, 09:39 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

I think I'm just going to replace the whole power board, but I figured I'd post what I found, just for posterity.

I got the heatsink removed, or at least freed it from the board so I could get at the FETs. D751A is not a normal N-Channel FET, but a double diode rectifier (STTH2003CFP: https://www.st.com/resource/en/datasheet/stth2003.pdf). I left this rectifier in-circuit, so I'm not sure if my results are accurate, but testing for conductivity based on the diagram in the provided link showed what one would expect (conductivity in the forward bias on the respective pins, but not reverse). I believe that means this rectifier is working properly.

Q750A is an N-Channel MOSFET however (TK20A25D: https://toshiba.semicon-storage.com/...dName=TK20A25D). I had to completely remove this component to test it, but the rudimentary test results looks like the this FET is shorted, or at least damaged in some way. No matter what combination of Gate-Drain-Source I tried, I only ever saw results when the positive probe was on the source, and the negative probe was on the drain, and the reading on the DMM was always the same (all of the articles/videos I saw said that N-Channel FET tests always have the black probe on the source pin).

Thank you to everyone for all of your help. I'll post back here once I've received and replaced the power board to confirm whether or not that resolved all of my issues.

Attached Files

**budm** · 04-05-2020, 10:10 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

"D751A is not a normal N-Channel FET"
'D' designator is for Diode.
'Q' desinator is for Transistor/MOSFET.

"No matter what combination of Gate-Drain-Source I tried, I only ever saw results when the positive probe was on the source, and the negative probe was on the drain"
That result is correct, you are measuring the Body Diode which you can see the symbol in the spec sheet. If that MOSFET is shorted out between S and D the meter would have shown conduction in both direction. G and S or G and S should show open circuit.

**heathloder** · 04-05-2020, 10:23 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

Ah, that makes sense. I appreciate the explanation.

Then perhaps my multimeter isn't putting out enough voltage to charge the MOSFET? I tried doing the diode test between the drain and source, just to verify that it read Open, and then I briefly touched the positive probe to the gate, and then checked the drain again, and it still read Open. Everything I read said that touching the positive probe to the gate should have made the drain conductive relative to the source.

Am I doing the test incorrectly?

Lastly, I'm not sure what you mean here - I think one of them is a typo:

G and S or G and S should show open circuit.

I apologize in advance for my naivety, and I really appreciate the assistance.

**nomoresonys** · 04-06-2020, 06:13 AM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

Originally posted by heathloder View Post

I think I'm just going to replace the whole power board, but I figured I'd post what I found, just for posterity.

I got the heatsink removed, or at least freed it from the board so I could get at the FETs. D751A is not a normal N-Channel FET, but a double diode rectifier (STTH2003CFP: https://cdn.badcaps-static.com/pdfs/...2d521d39bb.pdf). I left this rectifier in-circuit, so I'm not sure if my results are accurate, but testing for conductivity based on the diagram in the provided link showed what one would expect (conductivity in the forward bias on the respective pins, but not reverse). I believe that means this rectifier is working properly.

Q750A is an N-Channel MOSFET however (TK20A25D: https://toshiba.semicon-storage.com/...dName=TK20A25D). I had to completely remove this component to test it, but the rudimentary test results looks like the this FET is shorted, or at least damaged in some way. No matter what combination of Gate-Drain-Source I tried, I only ever saw results when the positive probe was on the source, and the negative probe was on the drain, and the reading on the DMM was always the same (all of the articles/videos I saw said that N-Channel FET tests always have the black probe on the source pin).

Thank you to everyone for all of your help. I'll post back here once I've received and replaced the power board to confirm whether or not that resolved all of my issues.

Next time just clip the diode, middle of the leg for testing if they test good then you just solder it back together, that's to make the test easier, since this one is bad it needs de-soldered from the back of the board and replaced with similar diode.

**heathloder** · 04-08-2020, 05:29 PM

Re: Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

I ordered a new board from tvpartstoday.com - the order was cancelled the next day citing shortage of inventory. The only other option currently available is on Ebay, comes from the UK, and costs $120 (unless I want to send the board out for repair). Therefor, I've decided that I'm willing to attempt to repair this board.

I removed D752 and retested, just to confirm that it actually failed. It did. I clipped D753 and tested it, and it looks good (.314V forward, OL reverse).

I also realized that my earlier tests of Q750A probably weren't good because my voltmeter only generates 1V for diode tests (verified using a spare analog multimeter used as a voltmeter), and the gate threshold for that FET is 1.5V-3.5V. I attached Q750A to an ESR meter I had hanging around, and I've attached it's output, making me believe that the FET may still be good.

That being said, I've ordered a handful of 5A 150V Schottky diodes in order to replace (at least) D752, and I'm going to try to reinstall Q750A.

Just for kicks, I plugged the mains and the motherboard back into the power supply (with Q750A and D752 removed), and applied power - I left the backlights unplugged for this test. The TV did not turn on instantaneously anymore - it remained in standby. When I press the power button in this state, the TV powers on (the buzzing no longer occurs), and I actually get a white status LED on the "flatbar" just beneath the display. After about 5 seconds, I get a cycling "6-blink red LED" error code. This seems like good news to me. At least it seems to indicate that removing the diode/FET from the circuit (I assume this is the LED driver area) prevents the behavior exhibited before, allowing the TV to "boot/pre-boot" and provide more diagnostic feedback than before.

If anybody has any other advice before I replace D752 (anything else I should check/try), I'm all ears.

Thanks for all the help that has already been provided - you guys are great! I'll continue to provide updates as I'm able.

Attached Files

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Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

Sony XBR-65X850E - has standby 3.3V, but won't power on - no status lights

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