Lcd tv power supply producing a high pitched and static noise. No picture but sound.

[funtastic]

Hi There,

I recently bought a faulty Sanyo 32" lcd tv 32XA2 and am hoping to fix it.

I've taken it to pieces and have narrowed it down to the power supply that is making a high pitched squealing when it's plugged in and when I push the power button it changes to a static/electrical sound in the same place. Also the tv sound comes on for around 4 seconds and then stops. The screen stays black, no back light or anything. The power led stays red.

I've checked all the capacitors and they are all fine.

I've attached a zipped file of the sound and a picture of where a bouts on the power supply it seems to be coming from.

Hoping somebody will be able to tell me what component I need to replace.

[randtek]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

The power supply squealing does not mean the problem is in the power supply. Squealing is a common symptom of shorted components in other circuits causing excessive load on the power supply.

In order for us to be able to help you, you need to post some photos of the TV and circuit boards. They should be clear, and high enough resolution so we can read lettering on boards and components. Ideally a photo of the TV with the back off, showing the location of all boards, then detail photos of each board. You will also need a voltmeter to troubleshoot this kind of problem.

[funtastic]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

Hi there,

Thanks for the reply. I will post pictures tomorrow as it's late here and need better light to take decent pictures. I do have a voltmeter.

[funtastic]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

Hi There,

I've taken the best pictures I can. I've also attached a pdf with a few pages from the service manual. There's a picture of the solder side of the power supply of one spot that was brown, not sure if it's just where it's heated and the flux has come out of the solder?

I decided I'd pull all the cables out of the power supply and then plug it in and it still made a soft static sound in the place I pointed out before. Wouldn't this just indicate something wrong in the power supply? Also when I just plugged in the board in the middle, the power supply sound increased. This was the only board that made a difference to the sound.

[funtastic]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

Could someone please help me out?

[tw2005]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

You really need to check the voltages from the PSU when you turn it on to get an idea where to start. At least that would be my first step.

If you disconnect the 2 connectors for the inverter at the psu what happens?

[funtastic]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

Just an update the tv sound works fine it doesn't cut out.

Pulling out the two connectors for inverter do nothing, the sound remains the same.

I do have a multimeter but how do I check the voltages when there's no indication on the board or cables of what pin is which. Any suggestions?

[funtastic]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

Hi,

I've checked all the pins on the connectors. Only two out of five connectors are receiving power. The other three aren't getting anything. I've attached a picture of which ones.

So the inverter is getting no power and the signal board the one with the video outputs.

Where and what should I test now? I have no idea myself.

[funtastic]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

I have no idea what to test on the power supply I meant.

[funtastic]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

I didn't know that I had to start the tv up to get a reading on the multimeter for the connectors, I just had it plugged into the wall. So now there is power on the connectors. Maybe the soft buzzing on the power supply is normal and it's the inverter with the problem?

Wish someone experienced would help me out here.

[mattpd]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

A bad inverter would most likely just cause your backlight to go out. If you turn on the tv and shine a light into the screen can you see an image?

[funtastic]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

Hi, i've tried that and no no image unfortunately.

[drpj23]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

Could you list the voltages you are getting out of each pin? per connecter?

Ex:
CN56 (may be helpful to note where these go)
1: 5.65v
2: 0v
etc.

[funtastic]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

Hi,

I thought I had already tried that but I hadn't and turns out your right. Thanks for that that's what's wrong.

[drpj23]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

Bad inverter?

[funtastic]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

It was the inverter that's stopped working. There's no power coming out of the outputs of the inverter. Is there anyway to fix this or do I need to buy a new one? I've checked the caps on it and they seem fine. The power is coming into the inverter fine it's just stopping somewhere.

[drpj23]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

Your meter wouldn't be able to test the output of those transformers, it is way too high and can damage your meter. (but since we have no output you probably are fine)

Is there a fuse on the inverter board? (May have to remove the black covering) If that is OK then...

First we need to see the voltages getting to the inverter. Beside the 24v, there is a BL_ON somewhere on there too, so we need to check if the main is telling the inverter to actually cut on.

Lastly, if you could remove the black covering over the inverter and include a good pic of that, that would be swell too.

[funtastic]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

Hi drpj23,

Voltages are:

Connector 1

Pins:

1-5. VBL 36.3v
6-10. GND 0.06v

Connector 2

1-4. VBL 36.1v
5. SYN 0.00v
6-8. GND 0.06v
9. SEL 0.06v
10. E_PWM 0.26v
11. I_PWM 0.38v
12. BL_ON 7.19v

The pin labels are what was on the reverse of the Inverter Board. The power supply board had no indication of what each pin was.

Not sure if there is a fuse on the inverter but I've attached a pic so could you tell me please? Let me know if you need a better picture?

[tom66]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

Left of "CMO" there is a white surface mount fuse.
There are two others on the board elsewhere.

[budm]

Re: Lcd tv power supply producing a high pitched and static noise. No picture but sou

Beside the white fuses, check that black fuse also. B+ of 36 Volt seems very high.