Bush 7080 - Fading Sound In One Channel Problem

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MyOhMy

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Jul 26, 2015
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Hi all,

I managed to acquire this little beauty, a Bush 7080. It's above Mini status, fitting more into the smaller side of Small boxes. It's neat, tidy, compact, has all front controls and is a pretty good looker.

DSCF1508sfw.jpg

Issues and/or problem areas:
1. Broken handle: will fix or replace in due course.
2: No sound from tape deck although transport moves & spindles turn: to be rectified.
3: Snapped of case securing lugs: Fixed.
4. Requires a service: All done for the most part.
5. Gradual fading to silence of sound in left channel only: Found when using radio, needs fixing. Right channel is working normally.

On the 5th point, I've searched the forum for answers and taken all the excellent advice I could find including cleaning the micro switch by the AC In, this works just fine.

Now, if I apply pressure and press the 'Balance' knob in a downwards direction for a second or two (akin to trying to push over a flag pole set in the ground) , the sound will be immediately restored to the left channel but will gradually fade again to silence if the pressure is released from the 'Balance' knob. Repeating the pressure on this knob returns the sound and the sound will fade again once pressure is relieved. No other switch, knob, control or function seems to have any effect on the sound (other than the 'Off' switch and volume control!).

In my less-than-expert analysis following the advice & comments on the forum, and in the absence of any other reason I can think of, I have concluded that the problem most likely lies within the 'Balance' pot. From a close outward inspection I've noticed no apparent damage to the pot or soldering, it is sited firmlty and there is no perceivable movement of the pot when gently 'wiggled'. The pot shaft rotates smoothly and without hindrance.

Would I be correct in thinking the a problem exists within the pot and would this pot need removing for assessment (gulp!)?

Pot pics, I can take more pics if required:
DSCF1529sm-sfw.jpg
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DSCF1532sfw.jpg
 

Reli

Member (SA)
Dec 24, 2010
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Nice box. Probably a Sanyo AKA.

I have the same problem with a Telefunken Studio 1. If I put downward pressure on the knobs, the sound is good, but if I don't, it's not.

So I'm guessing either a damaged solder joint, cracked board, or worn brushes inside on of the knob pots.
 

MyOhMy

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Jul 26, 2015
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I've examined with a magnifying glass as much as I could without seeing any cracks to solders, traces etc. so the next stage would be to open up the pots and see what this may reveal. All in good time.
 

BoomboxLover48

Member (SA)
Dec 3, 2010
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Before attempting any evasive procedures I would clean the balance pot with a little Deoxit and see if that makes any difference.

Like Reli mentioned any cracks on the soldering or board can also cause this.
 

caution

Member (SA)
Mar 25, 2014
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Boomboxery
Luckily that's a pretty common one, unless the shaft is an odd length you could replace it if nothing else fixes it

If you take it apart, check if the feelers are all sitting at the same height, sometimes one may need to be bent up a tad so they're all under similar tension against the carbon track, without your help by pressing on it.

Royce, did you mean to say invasive maneuvers? :hmmm:
 
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