This is a PN64E8000GFXZA TV that I've had for about 8 years. It has occasionally 'glitched' where it would go off periodically and then come back on with no issues for weeks. Last week it went 'pop' while my wife was watching it and then it runs up past the splash screen, but then as soon as it displays an actual picture for maybe 1 second, it does the click, power cycle and keeps going around that loop, picture appears, and then it reboots.
So we bought a new TV but, being an EE, I wanted to check the blown one out. I took out the SMPS PCB which is BN44-00516A and, straight away, I could see that one of the pins of the QP802 FET was burnt, see picture. The source pin which goes to ground was open cct from the PCB because the track had blown around it roughly where I've drawn a red circle (see 2nd picture). [EDIT] I measured the FET after removing it and it's single-digit ohms between any 2 pins so it has clearly applied high voltage to the components on the source and gate pins although the source is directly to a big ground track which is why it blew the copper around the pin; the gate obviously tried to feed high voltage to RP803 & RP804 and they are open cct too.
I can't find a schematic for the BN44-00516A but I've found the cct for the BN44-00333A and the circuit for ICP801 driving QP802 & QP804 on my PCB seems very similar to the 333A schematic where ICP801 drives QP802 & QP803. If anyone can provide the actual 516A schematic that would be great.
It appears that the circuit is a dual phase switcher where the cct associated with QP802 is the same as that associated with QP804 but, in my bad PCB, many of the components between QP802 and the push-pull pair QP807/8 are blown e.g. R803/4 are both open circuit (5 Meg).
I've ordered a repair kit that includes many major parts but the concern is that ICP801 is blown or at least the side that drives QP802 may have been damaged.
I'll end this post here but any input, advice or comments are welcome and appreciated.
So we bought a new TV but, being an EE, I wanted to check the blown one out. I took out the SMPS PCB which is BN44-00516A and, straight away, I could see that one of the pins of the QP802 FET was burnt, see picture. The source pin which goes to ground was open cct from the PCB because the track had blown around it roughly where I've drawn a red circle (see 2nd picture). [EDIT] I measured the FET after removing it and it's single-digit ohms between any 2 pins so it has clearly applied high voltage to the components on the source and gate pins although the source is directly to a big ground track which is why it blew the copper around the pin; the gate obviously tried to feed high voltage to RP803 & RP804 and they are open cct too.
I can't find a schematic for the BN44-00516A but I've found the cct for the BN44-00333A and the circuit for ICP801 driving QP802 & QP804 on my PCB seems very similar to the 333A schematic where ICP801 drives QP802 & QP803. If anyone can provide the actual 516A schematic that would be great.
It appears that the circuit is a dual phase switcher where the cct associated with QP802 is the same as that associated with QP804 but, in my bad PCB, many of the components between QP802 and the push-pull pair QP807/8 are blown e.g. R803/4 are both open circuit (5 Meg).
I've ordered a repair kit that includes many major parts but the concern is that ICP801 is blown or at least the side that drives QP802 may have been damaged.
I'll end this post here but any input, advice or comments are welcome and appreciated.
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