Hitachi 32LD6600B speakers always emit low whine

[DoctorWedgeworth]

Hi,

I got this given to "take to the dump" about a year ago because it wouldn't turn on. A few capacitors were blown so I replaced them and it turns on and works, but there's always a low hum coming from the speakers.

I thought I'd try again to fix this. I'm not sure if it was like this before the caps blew or if I'm partially responsible (I'm *very* amateur with electronics, please be gentle). I figured it might be a slight voltage on the earth (?) coming through the speakers so thought maybe I'd shorted it somewhere. I just checked the traces and scraped lines in a couple of places where it looked possible, and repositioned a capacitor directly connected to the speaker so the legs were a little further apart but it's still happening.

The noise comes from both sides, constantly. It's low enough that you don't hear it if watching a loud film, but any quiet moments are replaced by the noise. There's no silence. And to add to my problems my DMM won't turn on

Any idea where I should start? It's only for a hobby so no big deal if I don't fix it, but please treat me as though I know nothing!

Thanks.

[ron77]

Re: Hitachi 32LD6600B speakers always emit low whine

I can tell you where to start. You have to look at audio circuit and its power supply,at least to start with. As you mentioned yourself, could be earth loop problem, but I wouldn't start there.

First,turn volume down.If hum is still there, could be problem in ht supply to
audio amp. However, if hum goes, could be more likely inputs to audio amp.This is only putting things simply.

The psu in your set is probably 17pw15-8. The 24v rail from psu is ht supply to sound amp. So you could check capacitors on that rail.Also check c877 and c878 they can affect quality of 24v supply.

You should have separate sound amp board on your model model. Could be problem problem in I/c there, but not top of my list. A small start for you.One last thing, worth checking two caps on invertor board.They are on the 24v rail.

[tom66]

Re: Hitachi 32LD6600B speakers always emit low whine

I have fixed many vestels using 17PW15/20 supplies and they all make the annoying low whine. I think it's a "feature" of them.

[ron77]

Re: Hitachi 32LD6600B speakers always emit low whine

Can't agree with you on that one, Tom. Use same type of vestel tv as my computer monitor. No noise from speakers or psu. I checked before I wrote my piece.

[tom66]

Re: Hitachi 32LD6600B speakers always emit low whine

I've always heard a slightly white noise sound. Maybe I'm just unlucky or I'm hearing higher frequencies.

[ron77]

Re: Hitachi 32LD6600B speakers always emit low whine

I can tell you where to start. You have to look at audio circuit and its power supply,at least to start with. As you mentioned yourself, could be earth loop problem, but I wouldn't start there.

First,turn volume down.If hum is still there, could be problem in ht supply to
audio amp. However, if hum goes, could be more likely inputs to audio amp.This is only putting things simply.

The psu in your set is probably 17pw15-8. The 24v rail from psu is ht supply to sound amp. So you could check capacitors on that rail.Also check c877 and c878 they can affect quality of 24v supply.

You should have separate sound amp board on your model. Could be problem in I/c there, but not top of my list. A small start for you.One last thing, worth checking two caps on invertor board.They are on the 24v rail.

.

[DoctorWedgeworth]

Re: Hitachi 32LD6600B speakers always emit low whine

I got distracted and forgot to check replies. Thanks for the help. The TV stops humming on mute, but any other volume has the same volume hum. I'll check those capacitors again.

As for c877 and c878, are you recommending I should replace those capacitors even if they aren't bulged?

[tom66]

Re: Hitachi 32LD6600B speakers always emit low whine

They don't usually bulge when they fail.

[DoctorWedgeworth]

Re: Hitachi 32LD6600B speakers always emit low whine

Would a failure of them not cause more problems than just sound whining?

[tom66]

Re: Hitachi 32LD6600B speakers always emit low whine

Normally causes general power issues. I'd apply the fix if you want it to last, but I would doubt it would sort the problem with the whine. For that, you would need a scope to trace through the noise and find where it's getting in.

[DoctorWedgeworth]

Re: Hitachi 32LD6600B speakers always emit low whine

Those two capacitors (c877 and c878) are cuboid capacitors - I didn't even realise they were caps if you need more confirmation about how amateur I am. They're MMKP82 but I'm not sure where I can get those from, are those all the same rating? Is there any way to tell if they need replacing without a scope (or a DMM, haha)

[tom66]

Re: Hitachi 32LD6600B speakers always emit low whine

At the very least a DMM is essential. Sometimes a can of freeze spray and a hairdryer can track down temperature sensitive components.

[DoctorWedgeworth]

Re: Hitachi 32LD6600B speakers always emit low whine

My DMM won't turn on and I need it to fix it I'll probably pick up another cheap one soon, but would it any use with these capacitors?

[tom66]

Re: Hitachi 32LD6600B speakers always emit low whine

Check 24V/12V output to see if they are stable...

[DoctorWedgeworth]

Re: Hitachi 32LD6600B speakers always emit low whine

Fixed this in the end. I noticed there was a wire from earth screwed to the main chassis but it wasn't screwed tightly and wobbled a little. Screwing it tighter fixed the problem. This wire was before the PSU board - it came straight off the plug socket.

Now my own problem is that it's a terrible TV in general