Medion MD7223TH LCD TV - PSU buzz/hum and turns off...

[markie76]

Hi,

I have a Medion MD7223TH 22" LCD tv which is sort of working but

1. There is a constant high pitched buzz/hum coming from the PSU - visual inspection shows caps all looking ok.

2. It randomly switches itself off to standby, could be after 2 hours or 30 minutes.

PSU.

PWB-0653-02
P/N: 5000100082
HJA080348000838

Any tips?

Or does anyone know who might be able to supply a PSU or repair it?

Thanks,

Mark.

[markie76]

I think the 'transformer/inverter' on the live side is making the noise (in the pic its under the metal shield on the left of the pic) - I don't know if you can buy these or have to make them as they as custome wound???

Pic;




http://i43.tinypic.com/2dv4y0l.jpg

[tv tony]

if you trace it out it may be the pfc choke, is it connected before the bridge rectifier? ie, on either pole of the mains, and are the wires on its in and out similar gauge, and finally are there just 4 pins wired, there may be more pins for location purposes, if you can ascertain this we can deduce it could be passive pfc. in which case using a simple formula we can work out the value of choke, inductor you require
regards
tony walker

[markie76]

Hi Tony,

Ok, I've tried to break down your post;

to confrim the pfc choke is the big ring with enamelled wire wrapped around it covered in shrink wrap?(circled red in pic below)

is it connected before the bridge rectifier?
Yes, it looks like 2 of the pins feed into the centre two pins of the bridge rectifier.

and are the wires on its in and out similar gauge
Yes, they all look the same guage.

and finally are there just 4 pins wired
Yes, just 4 pins.

Also, can you tell me what the component in the attachment is? It comes off the neutral and feeds into a circular blue disc (capacitor) - on the pcb it is marked NTC1 - the markings on it I can make out read '??SP 2R5'

The top of it is crumbling so I would be keen to replace it.

[tv tony]

hello again, the two items are thermistors, the are to limit any switch on surges, when cold they are high value but rapidly drop when they get warm, they lead a hard life.
re the transformer they can go noisy, ill look at work
regards
tony walker