Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

[DXseekerMO]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

I would like to thank everyone for all of your help. The parts for the PSU arrived this morning. I plan to install them this afternoon and will let know how it worked out.

[DXseekerMO]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

3Ω is low for the led of the opto, Did you replace the blown TL431? as for the opto 817b and 817b are the same.
I believe N881 opto is for turning on the backlight, so don't worry about that circuit now.

Something is not adding up since the Voltage on the main cap is stable but the output from the bridge is not, if output of the bridge goes up and down then the Voltage on the filter caps should follow.

Shopping list for this TV:

1P regulator:
https://www.digikey.com/product-deta...mSeq=286154013

OPTOs:
https://www.digikey.com/product-deta...mSeq=286187954

GB1:
https://www.digikey.com/product-deta...mSeq=286188767

Ok I got everything installed and without messing anything up! Stand-by voltage is still absent and hot side voltages up and down like before.

With the 1P regulator installed the short there is gone.

Ok, so where to from here?

[R_J]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

What was wrong with the v810 (1P) The "transistor" 1P is for turning on the backlight circuit
The "reference ic tl431" that was blown was the GB1 (N851), It's voltage was supplied from 12VQ, so I would check the diodes, on the T831 secondary, VD906/907 and VD819
Which opto coupler did you replace? or was it both?
I still think VZ810 16volt zener could be bad, it should have 16 volts on it.
Check the resistance on the 20 volt line to ground (VD825 cathode) or across C819.

[DXseekerMO]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

What was wrong with the v810 (1P) The "transistor" 1P is for turning on the backlight circuit
The "reference ic tl431" that was blown was the GB1 (N851), It's voltage was supplied from 12VQ, so I would check the diodes, on the T831 secondary, VD906/907 and VD819
Which opto coupler did you replace? or was it both?
I still think VZ810 16volt zener could be bad, it should have 16 volts on it.
Check the resistance on the 20 volt line to ground (VD825 cathode) or across C819.

v810, 1P transistor base and collector were shorted

VD906/907 check with expected diode readings. VD819 does not reverse bias but seems to have a low reading of .298 on both legs

Both OPTOs were replaced.

VZ810 has 6.87 to 6.95v across it.

Across C819 there is 99,700ohms

[nomoresonys]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

Maybe test your powerboard by itself, see if you get standby voltage and or more stable readings.

[R_J]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

Do you have a 16 volt zener diode that you can replace for VZ810? or a zener around that voltage (12-15v)? There should be 16 volts on that zener, If there is only 7 volts, that V812 whisch is acting like a regulator would only output 8 volts for VDD, this is not enough to keep N834 running

[DXseekerMO]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

Maybe test your powerboard by itself, see if you get standby voltage and or more stable readings.

The power supply was out of the TV during testing.

Do you have a 16 volt zener diode that you can replace for VZ810? or a zener around that voltage (12-15v)? There should be 16 volts on that zener, If there is only 7 volts, that V812 whisch is acting like a regulator would only output 8 volts for VDD, this is not enough to keep N834 running

I may be able to come up with one on another board. There look to be letter markings on the zener, is there a cross-reference somewhere I can use to turn those letters in to a datasheet to make sure I have the right one. or at least one that is close enough?

[R_J]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

MMSZ16T1G, I can't make out the letters from here.

[nomoresonys]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

And you're sure your rectifier diodes are ok?

[DXseekerMO]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

MMSZ16T1G, I can't make out the letters from here.

The letters are WK, picture below. The picture with two Zener's are on a scrap board. Will either of these work for testing?

And you're sure your rectifier diodes are ok?

Yes, just checked it again.

[nomoresonys]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

Does T902 check out ok?

[DXseekerMO]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

Does T902 check out ok?

Unfortunately I don't have a way to check transformers, therefore I don't know for sure.

[llonen]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

If your sure this is a psu board problem, then given the time I would probably opt for an used example, of which there seem to be several reasonably priced examples available to you.

https://www.ebay.co.uk/itm/Sharp-55-...8AAOSwhfxZb97g

[R_J]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

The WK diode seems to be a BZT52C13 13 volt zener, put one in and see if that voltage gets to 13 volts, if it does you know the original is bad, no weather the power supply will operate at 13 volts is boarderline
this part of the circuit could not be simpler, 160v through 3 series resistors (which you checked are ok) to the 16 volt zener, the voltage at the zener will be whatever the zener is.

[R_J]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

I misread post 50,
Here is a pdf of the zeners
And if you look at Diodes incorporated
WK = 16 volt
WM = 20 volt
WT = 39 volt
I would try and find something closer to 16 volts if you can, if not try the 20 volt

Some mfgr's list the WK as 13 volts but I will trust the schematic

[DXseekerMO]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

Well Satirday was a total loss for me, we had 55mph winds here and the power went out for several hours and then a friend of mine showed up and stayed for a while.

Hopefully today I will have time to continue on this.

[budm]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

BTW, you can use LED tester to test the Voltage of the Zener diode.

[DXseekerMO]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

BTW, you can use LED tester to test the Voltage of the Zener diode.

Out-of-circuit I'm guessing? I had no idea you could obtain their voltage that way, what a great tip budm! Thank you!

[budm]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

Yes, out off the board, the test current will be only about 30mA. Try it on known good Zener and see what the Voltage on the LED tester display will show.

[DXseekerMO]

Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

Yes, out off the board, the test current will be only about 30mA. Try it on known good Zener and see what the Voltage on the LED tester display will show.

I wasn't able to find a Zener in my pile yet, so I popped VZ810 off the board and with the backlight tester it passes 16.9v through it.

This has to mean it is ok.