Squealing PFC inductor on a Vestel 17pw15 power supply -what could be the cause ?

[Dannyx]

Good day folks. I've got this pretty "nasty" Myria LCD TV which, aside from bad picture caused by a bad AS15-F on the T-con board which I discussed in another post, also has a pretty loud squealing noise coming from the PFC inductor when the TV's on. When it's off, it's nice and quiet, since the inductor is not running. The noise becomes worse with the load: disconnecting the inverter for instance quiets it down a little bit, but it's still very noticeable nonetheless. It's WAY too loud, even for a SMPS - definitely not normal "switching" noise.
The power board is a Vestel 17pw15 and it looks pretty bad in design, compared to other PSUs I've seen (not necessarily Vestels). I've already replaced the caps encircled in green in the picture. What else should I check ? Should I replace the other red cap near the coil as well, or perhaps those two very dodgy-looking main filter caps (100uF) hot glued together and tied by wire ? It makes me really angry seeing those, so I'll probably replace them with a single 220uF cap (100uF+100uF). I've also noticed there's no snubber cap between the S and D of the FET driving the coil, so I was thinking of adding my own (see the picture for my idea)...would that work at all, or it would just blow up/not function ? Any way of quieting this thing down ?

[ReeceyBurger123]

Re: Squealing PFC inductor on a Vestel 17pw15 power supply -what could be the cause ?

Its something on the Pfc drive area, Ive never been able to sort it possibly a good idea to test the Pfc controller for low ohms to ground and other related devices like Smd resistors as they drift out of spec over time.

[Dannyx]

Re: Squealing PFC inductor on a Vestel 17pw15 power supply -what could be the cause ?

Its something on the Pfc drive area, Ive never been able to sort it possibly a good idea to test the Pfc controller for low ohms to ground and other related devices like Smd resistors as they drift out of spec over time.

Maybe it's indeed because of a missing snubber to suppress the "noise" that the FET makes which then resonates in the coil (which would make a me a genius ).

[Dannyx]

Re: Squealing PFC inductor on a Vestel 17pw15 power supply -what could be the cause ?

Its something on the Pfc drive area, Ive never been able to sort it possibly a good idea to test the Pfc controller for low ohms to ground and other related devices like Smd resistors as they drift out of spec over time.

The voltage across the main cap is 339v when the TV is on, with the inverter connected - WAY too low, so there's definitely something bad going on in the PFC. If I disconnect the inverter and power up again, the voltage goes up to 390v, so it seems that when a heavier load is applied, the PFC drive doesn't "pump" enough to keep the voltage constant. I don't think the inverter is at fault, since that coil still chirps even with the inverter unplugged (though not as loud, of course), so it seems the PFC is still "struggling" to keep the volts up. I checked most of the resistors around the PFC IC (which is an L6562D) and they all seem to be at the right values, with the exception of those 1004 ones (bottom right of the board in the second photo), which seem to read too low, but that seems to be a common issue when measuring high value resistors in-circuit, so removing them will probably reveal that they're OK as well. The IC itself could be faulty too, though my idea is that if that was the case, the TV wouldn't turn on at all.

[ReeceyBurger123]

Re: Squealing PFC inductor on a Vestel 17pw15 power supply -what could be the cause ?

Hmm that is low, I would start by testing ceramic caps near the pfc controller see if any are shorted then the controller its self.

[Dannyx]

Re: Squealing PFC inductor on a Vestel 17pw15 power supply -what could be the cause ?

Hmm that is low, I would start by testing ceramic caps near the pfc controller see if any are shorted then the controller its self.

I probably won't bother for now, just because the guy didn't pay for this: he came in with a bad AS15-F chip, so that's what I'll be tackling. If he wants me to investigate its supply as well, that'll cost extra and only then will I bother with it