Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

[Dannyx]

Greetings folks. I recently fixed this Vestel 17IPS20P power board inside a Philips TV (shorted output diodes that weren't even all the same >_>) and it's working fine now, except it's making this pretty loud and obnoxious hissing sound. It seems to be coming from that PFC coil (on the right next to the two red caps), though I might be wrong, since the noise is high pitched and hard to pinpoint. Usually such noises point to bad caps (the irony) causing lack of filtering, but without an ESR meter I can't go around changing EVERY cap on the board hoping the hiss would die down. I've already changed two of the 4 output caps, since they were rated at 16v and I put in 25v ones (the brown ones towards the right which are different from the 2 black ones next to them), but it didn't change anything. The noise starts when the TV is switched on and stops when it's switched off (DUUH). Its pitch doesn't change with the picture or backlight intensity. Has anyone experienced this ? Is it a cap issue at all ? Is it really that particular coil hissing, or is it the transformer next to it ? I'm perfectly aware it could be due to bad quality components, since these Vestel PSUs are absolute pieces of junk and it may be an inherent issue that you can't do anything about....

[vinceroger69]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

not sure if you have a circuit diagram but this may help
https://electronicshelponline.blogsp...d-circuit.html

[ReeceyBurger123]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

Try listen close to the Psu and see if its the transformers causing it.

[Dannyx]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

Try listen close to the Psu and see if its the transformers causing it.

Like I said, putting my ear as close as I safely could to the board, it seems to be coming from around that large coil, since there aren't any components in that area that could hiss. I tried using a plastic stick to tap and press some of the components, but not even the slightest change in the sound...could be a loose winding on a transformer or coil.

[vinceroger69]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

i use a cardboard tube the type that comes inside of kitchen rolls etc or even one from tin foil etc that way you can place the tube over the parts and put your ear on the other end safely.

[budm]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

https://www.badcaps.net/forum/attach...6&d=1474467079
The two inductors to the right of the two read caps are the LINE filter, the PFC inductor is the TR100.
So when TV is in standby do you hear the noise?

[Dannyx]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

https://www.badcaps.net/forum/attach...6&d=1474467079
The two inductors to the right of the two read caps are the LINE filter, the PFC inductor is the TR100.
So when TV is in standby do you hear the noise?

Like I said towards the bottom of my original post: no, when the TV is off the sound goes away. Also, I know those two identical coils are for line filtering and are not the culprit. The PFC coil is to the LEFT and down of the red caps in my picture.

[budm]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

'Like I said towards the bottom of my original post: no, when the TV is off the sound goes away' Sorry I missed that section.

[budm]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

BTW, what is the PFC boosted Voltage are you getting, 400 VDC?

[Dannyx]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

BTW, what is the PFC boosted Voltage are you getting, 400 VDC?

Haven't checked that yet, but I think it should be close to that, since the TV is working properly.

[Diah]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

i faced before on Philips 40PFL5507 with Vestel PWB TV working fine but PWB make noise like over load . when i disconnected the LCD by moving out the ribbon cable it work silent but no picture of course..

[budm]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

I do not know what the PFC Under Voltage shut down point is on this VESTEL board, Typical for Samsung is about 350V, if the PFC Voltage is lower but not at shutdown point, the TV will still function but the current through PFC circuit will increase so that is one possibility that the PFC circuit is making noise.

[Dannyx]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

I do not know what the PFC Under Voltage shut down point is on this VESTEL board, Typical for Samsung is about 350V, if the PFC Voltage is lower but not at shutdown point, the TV will still function but the current through PFC circuit will increase so that is one possibility that the PFC circuit is making noise.

Ok, but what could be causing such undervoltage ? Only those diodes I mentioned were busted - apart from that, everything seems fine.

[Dannyx]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

After using the "paper tube stethoscope" method that vinceroger69 suggested, it turns out it's not the PFC inductor that's hissing, but instead the main transformer (the blue one). Indeed, when I press my finger on top of it, the hissing does change a bit. I've replaced MOST of the caps, except the long 200v ones, so it could be due to the transformer itself.

[budm]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

Ok, but what could be causing such undervoltage ? Only those diodes I mentioned were busted - apart from that, everything seems fine.

There is feedback circuit that control what the Boosted Voltage output will be. If it is not low then that is not the problem.

[R_J]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

You say you replaced shorted output diodes "(shorted output diodes that weren't even all the same >_>)" What were the original numbers and what did you replace them with?

[Dannyx]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

You say you replaced shorted output diodes "(shorted output diodes that weren't even all the same >_>)" What were the original numbers and what did you replace them with?

Can't remember exactly, but of the 3 different types that were in there originally (all shorted but one), I chose the one with the highest ratings which I'm sure was an SB5100 so that's what I put in. No, the diodes don't go to different circuits - they all connect to the same trace on the back. They skimped out and didn't use TO-220 packs for some reason....

[R_J]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

I was just going by the diagram Budm provided and it has d207 and d208 (for the +24volts) as uf5402 which are ultrafast switching types
Did you change those or only the ones for the +12 volts (d209,d210,d205 & d505)

[Dannyx]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

I was just going by the diagram Budm provided and it has d207 and d208 (for the +24volts) as uf5402 which are ultrafast switching types
Did you change those or only the ones for the +12 volts (d209,d210,d205 & d505)

The ones I replaced are the 4 ones above and the the right the blue transformer in my picture, so those would be d208, d209, d210 and d211.

[R_J]

Re: Philips TV with badly hissing Vestel 17IPS20P supply, any solution ?

So all 4 are connected in parallel and only for one voltage? ( the diagram is a bit misleading)
The UF5402 are rated with a trr speed of 50ns
The SB5100 are rated with a trr speed of 500ns
since those are the diodes you replaced and that seems to be where the problem is its posible the diodes are not switchng fast enough causing the transformer to make the noise it is.