64PN5500 | BN44-00618A Main fuse keeps popping

nickgronk · 01-22-2022, 10:43 PM

Power supply board BN44-00618A keeps blowing main fuse and nothing plugged in to it.
I was gifted a 64PN5500AF, picture was amazing, but tv smelled like cigarettes and was dusty AF. I opened it up, blew all the dust out of it, removed PSB & main, and cleaned the metal underneath. Also blew all the dust off all other boards. Put the power supply back in, then mainboard. Soon as I turned it on there was a "pop".
The main fuse (T12AH250V) blew
I removed the power supply to be sure nothing underneath, all good. Soldered on a t12ah250v fuse and sure enough it popped again. Unplugged the mainboard and Y board - last fuse, it popped again.
I've ordered more fuses, but what can be the issue?

**diif** · 01-23-2022, 02:02 AM

There's usually a sheet of something under the power supply to stop it shorting on the back of the chassis, that's not fell off when you were cleaning has it ?
Photos will help us to see.
I think the model number is wrong, is it a PN64F5500AF ?

nickgronk · 01-23-2022, 04:08 PM

Yes you're right, it is a PN64F5500AF . There wasn't any sheet underneath, the risers are built into the sheet metal. Will take some pics of the PSB and get them posted

**dskall** · 01-23-2022, 04:11 PM

Unplugged and with main caps. discharged. Measuring across middle pins on bridge rectifier and across outer pins with multimeter on continuity should read open.

nickgronk · 01-23-2022, 06:52 PM

Both bridge rectifiers taken out of circuit to be sure. Both are perfect,

• On a whim, I replaced with another fuse from another PS board (same t12), did not solder in the bridge rectifiers (so none on the board), screwed the board back down, plugged in and turned on. Fuse is ok. ...

• Soldered the bridge rectifiers back in. Did not mount the board, laid it on rubber mat. Powered on and "zap" went the fuse.

**dskall** · 01-23-2022, 07:45 PM

What were the ohms on outside pins?

**nomoresonys** · 01-23-2022, 08:32 PM

Check, looks like NT801s, I believe it's the mov, it's green, looks like one of those blue ceramic capacitors but it's not a cap, located just right of where you plug the power cord in, check in diode mode, it should be open as in not beep and NOT read 000 which would mean short.

nickgronk · 01-23-2022, 08:43 PM

Quote:

Originally Posted by nomoresonys

Check, looks like NT801s, I believe it's the mov, it's green, looks like one of those blue ceramic capacitors but it's not a cap, located just right of where you plug the power cord in, check in diode mode, it should be open as in not beep and NOT read 000 which would mean short.

diode mode : .011 out of circuit

took out of circuit - fuse from old board intact. (running out of ceramic fuses... lol)

**nomoresonys** · 01-23-2022, 08:46 PM

Is it a constant steady beep?

**R_J** · 01-23-2022, 08:53 PM

Quote:

Originally Posted by nomoresonys

Is it a constant steady beep?

NT801s is a NTC thermistor, 11Ω is fine it does not read open.

**nomoresonys** · 01-23-2022, 08:53 PM

Ok, thanks RJ, I thought it might be the mov because I didn't see the mov anywhere else, does this tv not have one?

nickgronk · 01-23-2022, 09:09 PM

Quote:

Originally Posted by nomoresonys

Ok, thanks RJ, I thought it might be the mov because I didn't see the mov anywhere else, does this tv not have one?

this board has the NT801s . I shlud follow up. unable to read which side is which and dont think it should matter... dunno. but testing the legs of NT801s one side read 11ohm, switched leads read OL

EDIT: trying to remove the white goop, chip disintegrated.

**R_J** · 01-23-2022, 09:15 PM

Quote:

Originally Posted by nickgronk

this board has the NT801s . I shlud follow up. unable to read which side is which and dont think it should matter... dunno. but testing the legs of NT801s one side read 11ohm, switched leads read OL

It will read as a resistor, both ways. it is not the problem, check the mosfets mounted to the heatsinks, like QS802, QS804
and the pfc circuit mosfets like QP801c.
With no main board connected, it is likely the power supply is turning on all the circuits so a fault in any of them will blow the fuse.

nickgronk · 01-23-2022, 09:31 PM

Quote:

Originally Posted by R_J

It will read as a resistor, both ways. it is not the problem, check the mosfets mounted to the heatsinks, like QS802, QS804
and the pfc circuit mosfets like QP801c.
With no main board connected, it is likely the power supply is turning on all the circuits so a fault in any of them will blow the fuse.

Found another NT801s from a spare board, tested good, soldered in and zapped another fuse. will test fets .

Thank you everyone for all of your help! #SundayFunday

**R_J** · 01-23-2022, 09:39 PM

NT801s is just a current limiter for when the power supply is in standby, It gets shorted out by the relay contacts when the power supply is turned on.

**dskall** · 01-23-2022, 09:45 PM

Your problem will be on other side of bridge rectifiers. Probably fet.

nickgronk · 01-23-2022, 10:39 PM

Was both QS802 and QS804 - set is back online. Thanks a bunch!

01-22-2022, 10:43 PM	#1
nickgronk Member Join Date: Apr 2021 City & State: Ottawa My Country: Canada I'm a: Knowledge Seeker Posts: 24	64PN5500 \| BN44-00618A Main fuse keeps popping Power supply board BN44-00618A* keeps blowing main fuse and nothing plugged in to it.* I was gifted a 64PN5500AF, picture was amazing, but tv smelled like cigarettes and was dusty AF. I opened it up, blew all the dust out of it, removed PSB & main, and cleaned the metal underneath. Also blew all the dust off all other boards. Put the power supply back in, then mainboard. Soon as I turned it on there was a "pop". *The main fuse (T12AH250V) blew* I removed the power supply to be sure nothing underneath, all good. Soldered on a t12ah250v fuse and sure enough it popped again. Unplugged the mainboard and Y board - last fuse, it popped again. I've ordered more fuses, but what can be the issue?

01-23-2022, 02:02 AM	#2
diif Badcaps Veteran Join Date: Feb 2014 City & State: Midlands My Country: England I'm a: Professional Tech Posts: 6,006	Re: 64PN5500 \| BN44-00618A Main fuse keeps popping There's usually a sheet of something under the power supply to stop it shorting on the back of the chassis, that's not fell off when you were cleaning has it ? Photos will help us to see. I think the model number is wrong, is it a PN64F5500AF ?

01-23-2022, 04:11 PM	#4
dskall Badcaps Veteran Join Date: Oct 2016 City & State: Bakersfield ca. My Country: usa Line Voltage: 120VAC 60Hz I'm a: Knowledge Seeker Posts: 2,670	Re: 64PN5500 \| BN44-00618A Main fuse keeps popping Unplugged and with main caps. discharged. Measuring across middle pins on bridge rectifier and across outer pins with multimeter on continuity should read open. __________________ I assume no responsibility for any stupid suggestions I might post. Last edited by dskall; 01-23-2022 at 04:52 PM..

01-23-2022, 06:52 PM	#5
nickgronk Member Join Date: Apr 2021 City & State: Ottawa My Country: Canada I'm a: Knowledge Seeker Posts: 24	Re: 64PN5500 \| BN44-00618A Main fuse keeps popping Both bridge rectifiers taken out of circuit to be sure. Both are perfect, • On a whim, I replaced with another fuse from another PS board (same t12), did not solder in the bridge rectifiers (so none on the board), screwed the board back down, plugged in and turned on. Fuse is ok. ... • Soldered the bridge rectifiers back in. Did not mount the board, laid it on rubber mat. Powered on and "zap" went the fuse. Last edited by nickgronk; 01-23-2022 at 07:23 PM.. Reason: did some testing.

01-23-2022, 07:45 PM	#6
dskall Badcaps Veteran Join Date: Oct 2016 City & State: Bakersfield ca. My Country: usa Line Voltage: 120VAC 60Hz I'm a: Knowledge Seeker Posts: 2,670	Re: 64PN5500 \| BN44-00618A Main fuse keeps popping What were the ohms on outside pins?

01-23-2022, 08:32 PM	#7
nomoresonys Badcaps Veteran Join Date: Jan 2013 City & State: midwest My Country: U.S. I'm a: Knowledge Seeker Posts: 7,698	Re: 64PN5500 \| BN44-00618A Main fuse keeps popping Check, looks like NT801s, I believe it's the mov, it's green, looks like one of those blue ceramic capacitors but it's not a cap, located just right of where you plug the power cord in, check in diode mode, it should be open as in not beep and NOT read 000 which would mean short.

01-23-2022, 08:46 PM	#9
nomoresonys Badcaps Veteran Join Date: Jan 2013 City & State: midwest My Country: U.S. I'm a: Knowledge Seeker Posts: 7,698	Re: 64PN5500 \| BN44-00618A Main fuse keeps popping Is it a constant steady beep?

01-23-2022, 08:53 PM	#11
nomoresonys Badcaps Veteran Join Date: Jan 2013 City & State: midwest My Country: U.S. I'm a: Knowledge Seeker Posts: 7,698	Re: 64PN5500 \| BN44-00618A Main fuse keeps popping Ok, thanks RJ, I thought it might be the mov because I didn't see the mov anywhere else, does this tv not have one? Last edited by nomoresonys; 01-23-2022 at 08:56 PM..

01-23-2022, 09:39 PM	#15
R_J Badcaps Veteran Join Date: Jun 2012 City & State: ☻ My Country: Canada I'm a: Professional Tech Posts: 7,990	Re: 64PN5500 \| BN44-00618A Main fuse keeps popping NT801s is just a current limiter for when the power supply is in standby, It gets shorted out by the relay contacts when the power supply is turned on.

01-23-2022, 09:45 PM	#16
dskall Badcaps Veteran Join Date: Oct 2016 City & State: Bakersfield ca. My Country: usa Line Voltage: 120VAC 60Hz I'm a: Knowledge Seeker Posts: 2,670	Re: 64PN5500 \| BN44-00618A Main fuse keeps popping Your problem will be on other side of bridge rectifiers. Probably fet.

01-23-2022, 10:39 PM	#17
nickgronk Member Join Date: Apr 2021 City & State: Ottawa My Country: Canada I'm a: Knowledge Seeker Posts: 24	Re: 64PN5500 \| BN44-00618A Main fuse keeps popping Was both QS802 and QS804 - set is back online. Thanks a bunch!

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