Sony KDL-55EX620, no stand-by volts from one bad resistor?

[DXseekerMO]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

Yet another observation....While updating the post on the Samsung PN59D550 I left the power to the tv off. About 20min later I switched AC power back on. The TV came on and stayed on for quite some time, way longer than before but as soon as standby power went away the TV turned off.

Seems like the longer I keep AC power to the set off the longer it will stay on.

EDIT/ADD: Stand-by power also goes away when AC power is activated and the TV is off.

Stand-by power is also unstable sometimes.

Weird

[DXseekerMO]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

So after some circuit tracing, the stand-by connector pin is number 10 on CN6101 and traces to an optical coupler, location PH6302 and is an NEC 2561A. The other side of that opto traces in part to Q6301 and is an N1 transistor, the same one that looks a little crispy on my board. I re-loaded the pic of it below. Eventually the circuit on the anode/cathode side of that opto traces to IC6501 which is also known to fail.

Can anyone help me figure it out from here?

[R_J]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

If you lost standby voltage re check the standby circuit, make sure you have Supply voltage to R6201 and pin5 of ic6201
If you don't have 4.6 volts standby on C6251 (D6251 cathode) Q6301 will never be turned on
You likely have some cold solder joints somewhere.
Also check that R6001 is good

[DXseekerMO]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

Thanks for the reply R_J.

R6001 tests good.

I performed four tests:

Test 1: After the TV was unplugged for 20min and with CN6001 plugged in to the PSU, AC power was applied to the set. The TV was tested while off.

There is no voltage at either side of R6201 or pin 5 of IC6201
There was 4.45V at C6251 for a short time that became unstable and disappeared
There was 3.46V at the stand-by pin of CN6001 that became unstable and disappeared at the same time voltage at C6251 did.
There was 3.46V present at the power on pin of CN6001 that disappeared before 3.3VSB/voltage at C6251 did.
The TV did turn on and show a picture when the power on pin had voltage.
.
Second test: After the TV was unplugged for 20min CN6001 was unplugged from the PSU and AC power applied to the set.

There is no voltage at either side of R6201 or pin 5 of IC6201
There was 4.45V at C6251 that occasionally became slightly unstable but returned to 4.45V and remained.
There was 4.45V at the stand-by pin of CN6001 that became slightly unstable but returned to 4.45V and remained.
There was 0v present at the power on pin.

Third test: With AC power still applied CN6001 was plugged back in to the PSU:

There was no voltage at either side of R6201 or pin 5 of IC6201
There was 4.45V at C6251 that became slightly unstable but returned to 4.45V and remained.
There was 3.45V at the stand-by pin of CN6001 that became slightly unstable but returned to 3.45V and remained.
There is 0v present at the power on pin.

Fourth test: With the TV unplugged for 20min, CN6001 plugged in to the PSU and AC power applied to the set.

There is no voltage at either side of R6201 or pin 5 of IC6201
There is a stable 4.45V at C6251 that has now remained for 45min
There is a stable 3.46V at the stand-by pin of CN6001 that has now remained for 45min
There is 0V present at the power on pin of CN6001.

Yes, you are reading that right…after plugging CN6001 back in to the PSU with AC power still applied everything changed and now the only missing voltages are Power on and the supply voltage to IC6201. I've been monitoring SBV for more than an hour now and it's 3.46V with CN6001 plugged in and rock solid.

So it looks like there's a fault in the supply line of IC6201 and maybe the main board if power on voltages comes from/through it?

Thanks for your help R_J, I appreciate it.

[DXseekerMO]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

After leaving the TV unplugged for an hour I plugged it back in and continuously monitored the stand-by voltage at the PSU. It started at 3.44V, slowly rose to 3.46V and remained rock solid for an hour. Connector CN6001 was hooked up to the PSU.

I pulled the main board and traced the POWER ON circuit. It descends from the connector to the bottom of the board and appears to terminate at the SMD CAP pointed at with the orange arrow. I get a Vdrop across that cap of .560 in diode test mode. I traced the circuit from the other side of that SMD cap and it terminates under the processor pointed at with the red arrow.

At first I thought POWER ON would have been supplied by the main board, but when I see where the other side of that cap terminates and the numerous items also sharing the same area I now wonder if POWER ON comes from the PSU?

I get the same VDROP in diode mode when testing from the POWER ON pin at the MB connector to the termination point under the processor and zero VDROP on the POWER ON wire from the PSU to the main board. It looks like the whole POWER ON circuit has some level of continuity from the PSU to the termination point of that circuit.

So either I have a PSU or Main board problem with the POWER ON circuit, at a minimum? What do you think?

[budm]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

The Power on is 100% from the main board to feed power supply G6 board IC6151 pin 20 as shown in the main power supply circuit I provided, you see the pin circuit symbol that tells you if that is signal going out or receiving.
What is the DCV on main board CN6002 pin 9 AC_OFF_DET?
MAIN_PWR control signal (manual PDF page 16) of from IC9000 pin AC3 which go to CN6002 pin 8 (manual PDF page 22).
Did you look at the service manual I provided?

[DXseekerMO]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

Thanks for the reply budm, I did review the manual and had a look at those pages.

AC_OFF_DET pin is 0.46V
POWER_ON pin is 0V

A half-volt on the AC_OFF_DET appears a little low. I didn't see a target voltage value on that page.

I also traced the other side of the POWER_ON circuit on top of and under the board to check inline components. I'll have to check the manual to see if its either a fuse or resistor in that circuit but there were four of them side by side and they all tested the same on diode check mode, VDROP of .120

I guess the reason I traced them was to make sure the circuit has continuity from the processor to the connector pin on the MB.

[budm]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

AC_OFF_DET should be 3.3V for normal operation, see service manual PDF page 35. Also see AZ2-F training.
BTW, are you getting any error blinking codes?

[DXseekerMO]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

Early in the diagnostic the orange light blinked two times, pause, two times. When POWER_ON voltage was present it was staying on all the time. It no longer illuminates at all.

The missing AC_OFF_DET power looks like it comes from the G board. That would seem to make the most sense since AC is on that board. I guess that means I have a bit more detective work to do there? And if I am understanding this right it looks like the main board has a failure as well?

Or is the processor denying POWER ON because the AC_OFF_DET voltage is absent?

[DXseekerMO]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

On page 35 of the service manual I traced the AC_OFF_DET circuit back to that crispy looking transistor Q6405 and opto PH6301 and on to IC6501, pin 26. That IC must switch/make 3.3 or maybe 5V or something?

I could test to see if the voltage is there, but that IC is on the other side of the board. Is there a test point on the top side of the board for this voltage?

I suppose I could test that leg of Q6405 and leg 3 of PH6301 as well if I can find a test point?

[DXseekerMO]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

So I tested leg 1 of PH6301 and found 4.45V steady

I then tested leg 3 of PH6301 and had no volts

Just now I tested leg 4 of PH6301 and have 0V, but I do have 3.49V at leg 4 of PH6302

This means pin 26 of IC6501 has good output to the opto and the opto is not passing the signal through to transistor Q6405 to switch on the AC_OFF_DET voltage?

[R_J]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

When you are checking these voltages on the opto, what ground are you using?

[DXseekerMO]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

Chassis.

There is zero volts at leg 5 of transformer T6201. If I'm reading the schematic right this is significant?

There is no voltage present on that whole side of the transformer.

[R_J]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

Thats why, the power supply has HOT ground and COLD or chassis ground, you need to use HOT ground when checking voltages on the primary side.
HOT GROUND would be the [-] connection of C6521-C6526
Lets take PH6101 for example, pins 1 & 2 are on the cold side so use chassis to measure the voltage. Pins 3 & 4 are on the HOT or Primary side so you must use C6521 [-] for ground (hot ground)

[DXseekerMO]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

THANK YOU R_J!!!!! That got me straightened right out!

Pin 4 reads 18.6V Hot ground
Pin 3 reads 0V Hot ground
Pin 2 reads 4.45V Cold ground
Pin 1 reads 4.45V Cold ground

That means voltage IS present after the opto?

On Transformer T6201 there is main cap value voltage at pins 1, 2 and 3 and no volts on 5 and 6, hot ground used.

[R_J]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

I just used ph6101 as an example, which opto are those voltages for?
Pins 1 & 2 are the same voltage so the internal led will be off, so the optos output transistor will be open.

So whats the problem again?

[DXseekerMO]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

Sorry, PH6302

[budm]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

You understand how transistor work, correct?

[DXseekerMO]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

The problem is no AC_OFF_DET volts at CN6101

[DXseekerMO]

Re: Sony KDL-55EX620, no stand-by volts from one bad resistor?

You understand how transistor work, correct?

Maybe you should explain it to me....apparently I have something mixed up in the bean.....

It looks like the single lead side is supply voltage, the side that goes to ground switches the other side on so electricity can pass?