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Philips turntable humming problem
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Kidney



Joined: 08 Dec 2011
Posts: 7
PostPosted: Thu Dec 15, 2011 5:48 am    Post subject: Reply with quote
vtech wrote:
when you turn UP the volume control, it should get louder(much louder) and as you turn it DOWN, it will effectively short the same signal line to the ground effectively killing any hum noise

Hmmm...isn't this exactly what happens in my video? In the beginning (0:00-0:05) hum fades in as I turn the volume all the way up, 0:40-0:46 I turn the volume down and back up - hum dies and builds up again, 1:02-1:04 I turn the volume down for the last time and away goes humming again.

Also, telling by the fact that humming dies the moment I short ground and signal wires coming from the stylus (tried this with a metal screwdriver shaft), the problem should be related to an open connection in stylus, right?
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA
PostPosted: Sat Dec 17, 2011 3:54 am    Post subject: Reply with quote
Perhaps I am mistaking but it just does not seem to react as it should(red control). There should be no hum whatsoever when you turn counter- clockwise all the way ( right before turnoff click). ---hard to tell for sure.
Any way to get a replacement pickup? Or do you have access to a scope to rule out the power supply/capacitor problem?
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Kidney



Joined: 08 Dec 2011
Posts: 7
PostPosted: Sat Dec 17, 2011 8:25 am    Post subject: Reply with quote
vtech wrote:
There should be no hum whatsoever when you turn counter- clockwise all the way ( right before turnoff click). ---hard to tell for sure.

Ah, you're right, when you listen carefully there's indeed some hum as long as the unit is turned on, even with the volume turned all the way down. That hum is not what's causing real trouble, though - it's barely audible to human ear (my condenser mic seemed to pick it up pretty loud). However, the hum I was originally referring to - the really loud one that's masking the actual audio - is what you hear only after the volume is turned up.

I have access to a scope at my school, but I don't know how to use one yet. Of course I could swap all electrolytic capacitors. I've got plenty of used ones extracted from working appliances. I've got a feeling it won't fix the turn-volume-up--get-lots-of-additional-humming problem, though. Getting a replacement pickup is unfortunately out of the question. I don't have one lying around and buying another is probably an overkill, considering the turntable itself cost five bucks.
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA
PostPosted: Sat Dec 17, 2011 9:58 pm    Post subject: Reply with quote
Ok , that clearly explains the hum in the video.
I've never been a fan of just replacing parts as a shotgun approach and very much prefer the "see-through-the-circuit" methode but I can certainly understand the situation here.
Not sure if you want to go thru the trouble of swapping the caps though? More than likely, you are not gonna have the value/physical shape ones.
In general, in the world of troubleshooting caps, you can always jumper the suspected cap with one with same or higher value as a quick means of testing.The only thing you must observe is polarity and be careful around voltage rails.
You mentioned having a scope at school and seem to have an unusual electronic knowledge/interest in fixing a turntable of all things! All I can say ...KUDOS AMIGO Cool
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