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Old 01-22-2022, 10:43 PM   #1
nickgronk
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Default 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?
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Old 01-23-2022, 02:02 AM   #2
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Default 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 ?
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Old 01-23-2022, 04:08 PM   #3
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Default Re: 64PN5500 | BN44-00618A Main fuse keeps popping

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
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File Type: jpg 20220123_174438.jpg (561.0 KB, 17 views)
File Type: jpg 20220123_174455.jpg (466.7 KB, 13 views)
File Type: jpg 20220123_174506.jpg (816.5 KB, 12 views)

Last edited by nickgronk; 01-23-2022 at 04:48 PM.. Reason: more details
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Old 01-23-2022, 04:11 PM   #4
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Default 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.
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Last edited by dskall; 01-23-2022 at 04:52 PM..
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Old 01-23-2022, 06:52 PM   #5
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Default 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.
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Old 01-23-2022, 07:45 PM   #6
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Default Re: 64PN5500 | BN44-00618A Main fuse keeps popping

What were the ohms on outside pins?
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Old 01-23-2022, 08:32 PM   #7
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Default 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.
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Old 01-23-2022, 08:43 PM   #8
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Default Re: 64PN5500 | BN44-00618A Main fuse keeps popping

Quote:
Originally Posted by nomoresonys View Post
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)

Last edited by nickgronk; 01-23-2022 at 09:06 PM..
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Old 01-23-2022, 08:46 PM   #9
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Default Re: 64PN5500 | BN44-00618A Main fuse keeps popping

Is it a constant steady beep?
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Old 01-23-2022, 08:53 PM   #10
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Default Re: 64PN5500 | BN44-00618A Main fuse keeps popping

Quote:
Originally Posted by nomoresonys View Post
Is it a constant steady beep?
NT801s is a NTC thermistor, 11Ω is fine it does not read open.

Last edited by R_J; 01-23-2022 at 08:59 PM..
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Old 01-23-2022, 08:53 PM   #11
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Default 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..
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Old 01-23-2022, 09:09 PM   #12
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Default Re: 64PN5500 | BN44-00618A Main fuse keeps popping

Quote:
Originally Posted by nomoresonys View Post
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.
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Last edited by nickgronk; 01-23-2022 at 09:24 PM..
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Old 01-23-2022, 09:15 PM   #13
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Default Re: 64PN5500 | BN44-00618A Main fuse keeps popping

Quote:
Originally Posted by nickgronk View Post
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.

Last edited by R_J; 01-23-2022 at 09:26 PM..
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Old 01-23-2022, 09:31 PM   #14
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Default Re: 64PN5500 | BN44-00618A Main fuse keeps popping

Quote:
Originally Posted by R_J View Post
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
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Old 01-23-2022, 09:39 PM   #15
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Default 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.
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Old 01-23-2022, 09:45 PM   #16
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Default Re: 64PN5500 | BN44-00618A Main fuse keeps popping

Your problem will be on other side of bridge rectifiers. Probably fet.
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Old 01-23-2022, 10:39 PM   #17
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Default Re: 64PN5500 | BN44-00618A Main fuse keeps popping

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