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GF-9191 Bass / Treble Sliders Inoperative

GF-9191 Treble Bass Slider Sliders Sharp GF-9191

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#1 mcroce

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Posted 09 February 2019 - 08:07 PM

Hi, I recently bought a fairly good condition Sharp GF-9191H off of eBay.  

 

So far, the only functional deficit that I can find is that the treble and bass sliders are completely inoperative - moving either or both of them produces absolutely no change in the sound.

 

I've got the unit completely disassembled right now for cleaning and I'm looking for recommended solutions on restoring function to the sliders.

 

I've ordered some DeOxit, and will use that, but because it's only these two sliders (the others work fine), and because it's a total failure (e.g. it's not intermittent or static-y) I suspect it's not just the contacts.  

Does anyone have any recommendations, before I reassemble the unit?



#2 MesaAZGuy

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Posted 09 February 2019 - 11:25 PM

Check to make sure there aren't any cracks on the PC board. Check for bad solder connections.  Aside from that, see if the DeOxit does any help when you get it.



#3 Northerner

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Posted 10 February 2019 - 03:40 AM

Yeh always switch clean first as it’s amazing what issues it’ll resolve then test again

#4 mcroce

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Posted 10 February 2019 - 04:11 PM

Thanks!  I'm new to using DeOxit, and to this type of slider potentiometer.  Can I clean the contacts adequately with it still mounted on it's PC board?  I think I can just apply it where the arrows are in this pic, is that correct?

 

https://drive.google...4UZvF7r2irwVtWP



#5 mcroce

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Posted 23 February 2019 - 10:34 PM

OK, I have the boombox reassembled.  The bass and treble sliders still don't work; have cleaned them well with DeOxit.    No visible cracks in the PCB.  Any ideas on testing the potentiometers to see if it's their failure or a connection??

 

Thanks!



#6 Superduper

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Posted 23 February 2019 - 10:57 PM

It is most likely the potentiometers.  The failure is common.  What happens is the brushes inside the control breaks off or gets loose and loses contact, or the pins that solder to the PCB have a break in the potentiometer resistor board.  To test, you probably need to remove the Pot from the PCB to be sure although you can possibly try to test it in circuit but the readings could be all over the place due to potential parallel resistances and confuse you.



#7 Fatdog

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Posted 24 February 2019 - 10:39 AM

There is a service manual in the Boomboxery library that might help.

 

http://www.mediafire...Manual.pdf/file



#8 docs

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Posted 25 February 2019 - 06:34 AM

If you google how to test a potentiometer and do a simple multimeter test, it will tell you if the actual tracks of the pot are good or not. Once you know the answer to this you can determine whether to open it up and fix what is likely to be brushes which have come unstuck from their mount.

if you get signs that the pot tracks are knackered by seeing readings which are waaaay off what the pots' value is, all is still not lost, you can restore the tracks with conducting silver paint. Good luck!





Also tagged with one or more of these keywords: GF-9191, Treble, Bass, Slider, Sliders, Sharp GF-9191