Hi all, long story follows so grab a cuppa
(all component ref's take off the BN44-00159A circuit)
I thought i had seen most faults on these types of plasma PSU (basically same as the BN44-00161A & BN44-00162A used in the 42" & 50 " Plasma models). i currently have 1 of each in for repair, usual problems initially which were dry joints around the Va FETS on 1 & a s/c Vs FET on the other.
Replaced all FETS & associated surface mount components which usually blow & resistance checks show correct readings around the FET's now. So , switch on (on the bench not TV) ground PS_ON & that should bring the PSU(s) up nicely right ? WRONG !
On both PSU's the PSU does start up & the Va tract generates 63v & all the lower DC voltages (5.3 ,12v 18v etc) but within a second the relays trip out. Also when the relays initially pull in you don't get the nice solid 'Click' that you should, it's a bit subdued. I'm happy that the Va & Vs circuitry is correct as i have even swapped the TX801 & 802 pulse transformers (in case of shorted turns) but that hasn't helped & the Va does generate correct voltages in the short time it's active.
I have obviously replaced the secondary caps as well plus several caps in the standby circuit but no joy, a second after clicking on it clicks off. Once it has clicked off you can not trigger it on immediately again, you have to wait for the DC in the 22uf/400v standby reservoir cap (CB801) to drop (possibly a clue there )
When you measure the voltage on CB801 at switch on the voltage does go to 400v DC so the PFC circuitry is being enabled but of course after the relays drop out it drops to about 320v DC
My immediate thoughts are the Protection circuitry is kicking in but the problem is how to check it, the voltages initially look good, nothing looks stressed & the protection kicks in so quick how the heck to narrow this down.
Maybe i'm having a silver moment & i've missed something basic but i reckon if i can find out what's causing this on one board i will find the same on the other.
Any ideas thought etc greatly appreciated.
Graham
(all component ref's take off the BN44-00159A circuit)
I thought i had seen most faults on these types of plasma PSU (basically same as the BN44-00161A & BN44-00162A used in the 42" & 50 " Plasma models). i currently have 1 of each in for repair, usual problems initially which were dry joints around the Va FETS on 1 & a s/c Vs FET on the other.
Replaced all FETS & associated surface mount components which usually blow & resistance checks show correct readings around the FET's now. So , switch on (on the bench not TV) ground PS_ON & that should bring the PSU(s) up nicely right ? WRONG !
On both PSU's the PSU does start up & the Va tract generates 63v & all the lower DC voltages (5.3 ,12v 18v etc) but within a second the relays trip out. Also when the relays initially pull in you don't get the nice solid 'Click' that you should, it's a bit subdued. I'm happy that the Va & Vs circuitry is correct as i have even swapped the TX801 & 802 pulse transformers (in case of shorted turns) but that hasn't helped & the Va does generate correct voltages in the short time it's active.
I have obviously replaced the secondary caps as well plus several caps in the standby circuit but no joy, a second after clicking on it clicks off. Once it has clicked off you can not trigger it on immediately again, you have to wait for the DC in the 22uf/400v standby reservoir cap (CB801) to drop (possibly a clue there )
When you measure the voltage on CB801 at switch on the voltage does go to 400v DC so the PFC circuitry is being enabled but of course after the relays drop out it drops to about 320v DC
My immediate thoughts are the Protection circuitry is kicking in but the problem is how to check it, the voltages initially look good, nothing looks stressed & the protection kicks in so quick how the heck to narrow this down.
Maybe i'm having a silver moment & i've missed something basic but i reckon if i can find out what's causing this on one board i will find the same on the other.
Any ideas thought etc greatly appreciated.
Graham
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