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My JVC RC 838: Channel Balance Issues Fixed!


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#1 chhchca

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Posted 11 March 2017 - 11:45 AM

First of all, my deeply felt thanks to those who started and contributed to the post "JVC / Victor  RC 838: Channel Balance Issues", for inspiration as well as insights.

 

It is so well known among RC 838 owners that one of the channels may not work properly. On mine, R channel will be dead in "Stereo" mode. You may hear from it, to a point, in certain other Mode or Modes, just because the design allows some audio signal to come through from the other channel for certain sound effects, as far as I understand. Information so far points to the failed audio related sliders as culprit in most cases. 

 

To work on mine, I carefully removed the chassis. With a scheme in hand, I quickly found I was still lucky because the Volume pot was working for both L and R channels. 

 

However, all other 3 - Bass, Treble and Balance sliders did have problem! If you look carefully and check closely with a good flashlight, you may visually find out what went wrong with them even without removing them from PCB.

 

Important clues include fallen contact brushes and uneven wears. What you need to do next is to remove and rebuild the failed ones. 

 

 

The photo below shows a fallen contact brush on the left:

 

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Here you can see the wears are uneven because 1 of the contact brushes became loose, or got off base entirely as in my case. Also worth noting is the pot for Balance (on the right in the photo, with "black & white stripes"), an M / N type pot that can be very hard to find on the market now:

 

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I glued it back using JB Weld, which was highly recommended by a senior member here for most plastics. I also took the opportunity to reinforce the brush that still held its position, with just a tiny drop of JB Weld.

 

This is also time to check the glue markings on the ends of each stripe. Don't hesitate to touch up with some conductive glue if you see ANY opening, or just a hairline crack there:

 

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To re-assemble, make sure to use the right tool to precisely control how far you can go and NEVER over-tighten:

 

Attached File  IMG_20170303_082031.jpg   415.32K   1 downloads

 

 

 

My unit started to work again after the 3 pots were rebuilt and put back. As I could see no other issues to attend to, I replaced the the tuning light with an LED and added LED's to the 2 VU meters as well, just to make it look nicer:

 


Attached File  IMG_20170313_133749.jpg   179.04K   2 downloads



#2 Fatdog

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Posted 11 March 2017 - 06:42 PM

Nice!!  You must have been gifted quite a bit of patience to finish that job.  :lol:   Those tiny brushes are super thin and love to go flying across the room with the slightest grasp.  :annoyed:



#3 chhchca

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Posted 11 March 2017 - 09:20 PM

Nice!!  You must have been gifted quite a bit of patience to finish that job.  :lol:   Those tiny brushes are super thin and love to go flying across the room with the slightest grasp.  :annoyed:

 

Thanks for the high praise!

 

It is true that the brush and other tiny parts flew and fell several times when I was trying to put them back. However, I knew this would happen and took serious precaution: the job was done in a clean and transparent plastic bag big enough to allow my hands to work inside. I'd run into big trouble if I had tried to do it in open air.



#4 baddboybill

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Posted 11 March 2017 - 09:40 PM

Great job!!!

#5 MyOhMy

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Posted 11 March 2017 - 10:08 PM

Good job and what a brilliant tip for future use.  :thumbsup:   I had a similar, but worse, problem with slider brushes (LINK with pics) so I appreciate the delicacy of the work.
 
Again: "Well done".  :yes:



#6 jimmyjimmy19702010

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Posted 11 March 2017 - 11:09 PM

Great work!! It's a pity JVC went cheap with the sliders on their high end boxes.

#7 Fatdog

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Posted 12 March 2017 - 01:08 AM

...the job was done in a clean and transparent plastic bag big enough to allow my hands to work inside. I'd run into big trouble if I had tried to do it in the open air.

That is actually quite genius of you.  Thanks for the tip!



#8 superlew

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Posted 12 March 2017 - 05:12 AM

Awesome thread. :thumbsup:

I've rebuilt many sliders, but never bothered to take pictures. People have asked me about the process, but it's very hard to explain what they'll find inside when they open them up. This will be a "go-to" link whenever I get asked the question in the future.



#9 chhchca

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Posted 13 March 2017 - 04:35 PM

Great job!!!

Thanks Bill! And I do enjoy reading your posts and I'd say they are truly informative.



#10 chhchca

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Posted 13 March 2017 - 04:56 PM

Good job and what a brilliant tip for future use.  :thumbsup:   I had a similar, but worse, problem with slider brushes (LINK with pics) so I appreciate the delicacy of the work.
 
Again: "Well done".  :yes:

I looked at the link you provided and saw your project, which is quite a challenge! Personally I haven't worked much on newer makes and models so I look forward to seeing more of your work.

 

I, too, worked on a Sharp GF A2 of outstanding condition but I could not resolve the mystery why the cassette deck eats tapes all the time.      



#11 chhchca

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Posted 13 March 2017 - 05:35 PM

Great work!! It's a pity JVC went cheap with the sliders on their high end boxes.

 

Thanks a lot Jimmy and I do share how you feel about these sliders. I know these sliders were also used on some high-end Sharp models and the availability for either NOS or used ones is so highly limited on today's parts market.  



 

...the job was done in a clean and transparent plastic bag big enough to allow my hands to work inside. I'd run into big trouble if I had tried to do it in the open air.

That is actually quite genius of you.  Thanks for the tip!

 

 

 

Awesome thread. :thumbsup:

I've rebuilt many sliders, but never bothered to take pictures. People have asked me about the process, but it's very hard to explain what they'll find inside when they open them up. This will be a "go-to" link whenever I get asked the question in the future.

 

Thank you both! By sharing our findings, ideas and resources here we'll enable ourselves to do much more. 



#12 JVC Floyd

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Posted 13 March 2017 - 06:26 PM

Where do you live at I might be interested in having you rebuild the sliders for mine.

#13 baddboybill

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Posted 13 March 2017 - 08:19 PM


Great job!!!

Thanks Bill! And I do enjoy reading your posts and I'd say they are truly informative.

Thank you as well. Also some info for reasons a tape would get eaten is that take up reel is not working corectly. Either a bad belt or bad tire. ;-)

#14 chhchca

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Posted 15 March 2017 - 02:08 PM

Where do you live at I might be interested in having you rebuild the sliders for mine.

 

Not a problem. I'm in Toronto, Canada. Let me know the pot job you want to do when you have time.



#15 BoomboxLover48

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Posted 16 March 2017 - 02:04 PM

 

Nice!!  You must have been gifted quite a bit of patience to finish that job.  :lol:   Those tiny brushes are super thin and love to go flying across the room with the slightest grasp.  :annoyed:

 

Thanks for the high praise!

 

It is true that the brush and other tiny parts flew and fell several times when I was trying to put them back. However, I knew this would happen and took serious precaution: the job was done in a clean and transparent plastic bag big enough to allow my hands to work inside. I'd run into big trouble if I had tried to do it in open air.

 

Basically you used a transparent chamber/enclosure like the watch repairers use. Nice idea.. 



#16 ELzekio

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Posted 17 March 2017 - 10:37 PM

After i rebuilt my sliders i was pretty much ready to go with by box. It is very important that all of the sliders are rebuilt and rebuilt correctly. There can be so much dirt in those sliders that flooding it with deoxit is not the way to go. It also desolves the silicone grease lube,

I was lucky enough to win a part unit for bid on ebay for ridiculously cheap like $30 plus shipping if that. So i have a couple extra sliders and materials if i ever need them.


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#17 Fatdog

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Posted 18 March 2017 - 12:14 AM

Nice unit, ELzekio.  :yes:   I have that same cassette too.



#18 chhchca

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Posted 18 March 2017 - 06:18 PM

After i rebuilt my sliders i was pretty much ready to go with by box. It is very important that all of the sliders are rebuilt and rebuilt correctly. There can be so much dirt in those sliders that flooding it with deoxit is not the way to go. It also desolves the silicone grease lube,

I was lucky enough to win a part unit for bid on ebay for ridiculously cheap like $30 plus shipping if that. So i have a couple extra sliders and materials if i ever need them.


attachicon.gifIMG_0658.JPG

 

Exactly, using Deoxit alone does not solve the balance issue and rebuilding the related pots is the way to go.

 

Yes. I too believe you are one of the few lucky ones to have a part unit behind your keeper! 



 

 

Nice!!  You must have been gifted quite a bit of patience to finish that job.  :lol:   Those tiny brushes are super thin and love to go flying across the room with the slightest grasp.  :annoyed:

 

Thanks for the high praise!

 

It is true that the brush and other tiny parts flew and fell several times when I was trying to put them back. However, I knew this would happen and took serious precaution: the job was done in a clean and transparent plastic bag big enough to allow my hands to work inside. I'd run into big trouble if I had tried to do it in open air.

 

Basically you used a transparent chamber/enclosure like the watch repairers use. Nice idea.. 

 

Definitely! This is where the inspiration comes. Very cost effective and helpful.