magnavox D8443

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stereomann

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Nov 17, 2010
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HI
my D8443 works but humed when powered on so i tried a 12 transformer from pc speakers & the hum went away
so does any one know how to fix the transformer or know what part on it would be causing the hum

also the tape player will rew ff but on play only the pinch roller was spining the & the reels are not
but when a tape is inside only one reel spins & it eats the tape
 

Beosystem10

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Feb 21, 2013
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By substituting in an external PSU and finding the hum gone, that suggests that the smoothing block (usually just a large, single electrolytic of relatively large value) and/or the mains filter capacitor is/are faulty.

The mains filter cap is the less likely suspect and the smoothing cap will be mounted close to the low tension side of the onboard PSU, I don't know how much knowledge of light current work you have, so excuse me if this is stuff you've already considered, but if you have no idea what to look for, the smoothing block will be the largest one of these:

that can be seen near the onboard PSU. Check its value in uF (microFarads) and if you can get your hands on a capacitance meter, desolder one end of the cap and check its value.
If the value isn't too far out of tolerance, then read up on the web about effective series resistance, another quality of a cap that can affect its ability to do its job.
Another sign that all isn't well, even before you start with the meter and the soldering iron, is to look at the end of the cap which has the lead exiting centrally through a non-metallic bung. If you see any sign of physical leakage there, usually a yellow or orange sort of crusty substance, then the cap should be removed and replaced.

While you're doing this, it's a good idea to check every electrolytic cap for signs of leakage. (the ones which are polarity sensitive, the other caps - non-electrolytics - are generally reliable with a few exceptions)

The hum you're hearing will be at the same frequency as the refresh rate of your mains supply, that'll be 60Hz in the USA.

The above is general advice that applies to most equipment, I'm not familiar with your machine so cannot tell you whether the mechanical transport fault is caused by a failed idler tyre or an equally failed belt, no doubt someone who's been inside one of these will advise on that point. :-)
 

Zedman

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Mar 7, 2013
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The advice given by Beosystem10 is all good and nicely explained.

The only thing I would possibly add is that sometimes audio eqipment can get humm which is a multiple of the mains input frequency from earth loops and poor earthing. Although Id expect this is quite unlike in a boombox.

Poor continuity between earth screws and chassis surfaces can act similary to a diode which may induce a hum that is twice the mains input frequency i.e. either 120hz or 100hz. All it takes is rejuvination of the earth screw bond i.e. loosten screw, tighten screw, to fix these problems.

Z

:-)
 

Alberto

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Jan 3, 2013
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stereomann said:
HI
my D8443 works but humed when powered on so i tried a 12 transformer from pc speakers & the hum went away
so does any one know how to fix the transformer or know what part on it would be causing the hum

also the tape player will rew ff but on play only the pinch roller was spining the & the reels are not
but when a tape is inside only one reel spins & it eats the tape
Bad Main gear, very common problem with that Magnavox D-8443. It breaks like a potato chip!!
Look up the post from "Vintagevolts" he is trying to get some fabricated out of nylon.
 
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