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

[DXseekerMO]

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

Have you replaced N851 ? If it is still in circuit and shorted, it could be shutting down the power supply by turning on the opto
"PIN6 is 6.6v to 11.1v up and down" That tells me the ic's startup cell is working, the ic should pulse the fet's gate and the fet should drive the transformer, this will give you the +20 volts on C819, so check that R821 & R823 are ok.
Also check that you have +160 on the V807 Fet

Ok I think we're getting somewhere. On the OPTOs my board's callout is N881 and 891. Both cold side pins of N881 show 3ohms resistance.

If I am seeing it right R821 and 823 are in parallel, Both 2R2 resistors and with 1.5 ohms across both

V807 has 166V

[DXseekerMO]

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

I have a similar OPTO with the same 817B markings on the case. Will this work long enough for testing the TV, or do I need to get one with the exact same markings on it?

[DXseekerMO]

UPDATE: OPTO replaced

I pulled the OPTO out of the board and checked it, same 3ohms across the cold side pins. I installed the same number OPTO but from a VIZIO power supply, no longer checks short but still no stand-by!

[R_J]

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.

[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.

I have not replaced the blown TL431 just yet. What I did do is have a look in my inventory list and found a near identical board (217654) from a LC-55N6000U.

TL431 definitely needs replaced. I'm looking for one similarly marked on another board to transplant for testing. Is there a list somewhere I can look at for compatible IC's with other markings?

I feel the need to go back to the up-and-down voltages off the bridge rectifier for just a minute, because when I fire off the 217654 power board the voltage at its bridge rectifier is rock solid.

I guess the reason I went back to this is to ask...do you think the shorted TL431 is causing the voltage fluctuation, or is the bridge rectifier suspect too?

Also, both boards have the same output specifications and pinouts. Can I substitute this board in place of my original to test the rest of the TV? If so I don't think I'd do that until I pull the main board and have a look for "crispies".

With all of the damage on the cold side of the board I'm wondering if the damage trickled down from the main board? It's a confirmed nearby lightning strike with immediate thunder and other cooked devices in the home.

[budm]

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

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.

[R_J]

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

The boards do look the same, so it should work. The TL431 is a Precision Programmable Reference. it is there as a reference so the 12 volts can be regulated by driving the optocoupler and controlling the N834's ouput. like I said before, almost all smps use this reference ic, usually in a to92 case. (3 leg through hole mount)

Budm: there is a diode (VD808 &VD804) between the bridge output (ac3) and the main filter cap in the pfc circuit, so the bridge voltage which is not filtered could change if the N834 ic is trying to start and stop, pulsing.

[DXseekerMO]

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

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.

This is the only device between the caps and the bridge rectifier.

[budm]

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

That diode (boost pre-charge diode) is part of the PFC Voltage booster circuit, the Voltage on the anode is 120Hz DC pulse.
See fig. 3

[DXseekerMO]

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

The boards do look the same, so it should work. The TL431 is a Precision Programmable Reference. it is there as a reference so the 12 volts can be regulated by driving the optocoupler and controlling the N834's ouput. like I said before, almost all smps use this reference ic, usually in a to92 case. (3 leg through hole mount)

Budm: there is a diode (VD808 &VD804) between the bridge output (ac3) and the main filter cap in the pfc circuit, so the bridge voltage which is not filtered could change if the N834 ic is trying to start and stop, pulsing.

Installed the P6000's PSU. Its good news and bad news. The good news....the best I can see the OSD appears OK......but with no backlights its hard to tell.

That diode (boost pre-charge diode) is part of the PFC Voltage booster circuit, the Voltage on the anode is 120Hz DC pulse.
See fig. 3

Do you agree with R_J's belief that the fluctuation is from the board trying to start? It sounds exactly like what that Samsung 50" EH5300 was doing and it sounds logical.

EDIT/ADD: Backlight availability on this TV is super lousy, either high dollar used or cheap from China, ebay seller christmas2carol and arrival from late march to the second week of april.

[R_J]

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

check the voltage on pin4 SW, maybe the tv also has a backlight issue?

[DXseekerMO]

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

check the voltage on pin4 SW, maybe the tv also has a backlight issue?

Pin4 SW voltage on the original board from the TV is zero volts. Or are you asking about SW voltage on the substitute board? If so the SW voltage on that board's pin is 2.89v and remains. Both anode terminals on the backlight connector come up to 177/200 volts then drops and remains low.

[R_J]

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

I believe the backlight/SW pin should be high to turn on the backlights, If the backlight voltage comes up to 170 volts and drops down, that usually indicates an open led string in the panel, Do the backlights flash and go outl? how many wires go to the backlights 2 or 4 ?

[DXseekerMO]

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

I believe the backlight/SW pin should be high to turn on the backlights, If the backlight voltage comes up to 170 volts and drops down, that usually indicates an open led string in the panel, Do the backlights flash and go outl? how many wires go to the backlights 2 or 4 ?

Yes they do, and when the TV is on I can see a few points of light on the screen where is looks like some of the LED's are very dimly lit. There are 4 wires to the LED strips

I know this is an edge-lit TV but it looks like a few working very weak LED's like they are in an array behind the screen.

EDIT/ADD: Here's the best price I've found on the LED strips for this TV on Ebay. Does anyone have any experience with this seller or the reliability of their products?

https://www.ebay.com/itm/2-PCS-New-5...4383.l4275.c10

[DXseekerMO]

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

That GB1 is a TL431 reference ic
Using hot ground, check if you have VCC on N834 pin 6, Also check for aprox +160v on pin 8. Then check the base of V812, it should have +16 volts (VZ810 is a 16v zener)

I went to find this GB1/TL431 to buy and there are several choices. Can someone please help me with what I need to know to order the right item?

[DXseekerMO]

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

Here's the best price I've found on the LED strips for this TV on Ebay. Does anyone have any experience with this seller or the reliability of their products?

https://www.ebay.com/itm/2-PCS-New-5...4383.l4275.c10

The TL431 is a Precision Programmable Reference.

I went to find this GB1/TL431 to buy and there are several choices. Can someone please help me with what I need to know to order the right item?

Anyone?? I'm trying to complete an order for several TV's tonight if at all possible.

[R_J]

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

AN431AN-ATRG1 is the original diodes incorporated number .5% tolerence
the AN431BN is 1% tolerence, digikey only stocks this one

One of these would likely work https://www.digikey.com/products/en/...=1&pageSize=25

[DXseekerMO]

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

AN431AN-ATRG1 is the original diodes incorporated number .5% tolerence
the AN431BN is 1% tolerence, digikey only stocks this one

One of these would likely work https://www.digikey.com/products/en/...=1&pageSize=25

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

Would these all work OK you think?

[R_J]

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

They should be ok.

[DXseekerMO]

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

They should be ok.

Sweet. Thank you R_J, I'm going to get the stuff coming for this. Looks like it will be a bit before I have another update.

I guess I'll go with those LED strips, worse come to worse they are protected by Ebay so hopefully they work out ok.