Jvc 838 sliders doubt

[838FAN]

Hello everyone! As I said in my introduction post a few months ago I bought a biphonic jvc-838 for little money at a flea market, it worked fine .... a few days .until the left channel died in stereo mode (in biphonic mode and expanded it worked), I said well, a clean contact will solve it, I applied it to the sliders and nothing changed. For work and personal reasons I had no more time to dedicate and archive the project. During this isolation (mandatory in my country) I decided to return it, Of course I tested if by chance the problem had been solved, but it was still the same. Then he decided to disarm it and that was how I got to this page, I actually disarmed it and from what I read in posts here, I was not so wrong thinking about sliders Decomposed, today I unsoldered the board of controls of the board of the amplifier and I started to take them apart, clean them and repair them. This is where I have the doubt, according to what I understand these sliders (except for the recording level controlsn) they are stereos, so why do I have only one contact brush on these sliders?
I really find it very strange but when disassembling the sliders this seems like this. Of course since I was repainting the contacts of the sliders with conductive silver paint, which I hope has solved the problem of the dead channel. can I test the correct operation of the sliders? each of these has one or two contact brushes (treeble bass and balance)?

I'm going to put a couple of photos of the sliders and the plate, not of the cabinet because it still has a lot of dirt (it even had a small cockroach on the dial)
Thanks for your time!!
regards
Mauro

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[ELzekio]

For those pics that show a missing slider contact, are they gone, or were you able to find any rattling around in the slider assembly itself. If you can find any of those contacts, then you would want to put them back in place and use some kind of epoxy like JB Weld to hold the contacts back place works really well.

If you can’t find any of those mini contacts, then good luck finding any part units online. There are people that have spare sliders in contacts, but nobody wants to part with them.

Suppose if it was an extreme emergency, you could get away with putting a couple equal value resistors on the balance Pot so at least you get 50-50 balance without a slider.

For the other sliders it’s a different story. If any of those contacts go out on any of the sliders, then I don’t think you will be able to get any signal through the boom box.

You can test the operation of the slider with a multimeter to make sure both channels are responding with a smooth change in resistance.

 

[Superduper]

I have spare NOS (new old stock) Alps stereo sliders. They will physically drop in as they are the same series and same manufacturer but have the incorrect resistor board values and tonal curve for this application. Additionally the knob shafts are slightly too long and the shell does not have the same step. I use them to cannibalize the slide contacts to repair the ones in the M70 and RC-838. It's tempting to just remove the entire slide assembly (nylon part with the feeler contacts) but it's better to remove and glue the contacts instead. The nylon block assembly will actually drop right in as it is identical and I actually did exactly that on an earlier RC-838 rebuild, but the shafts are too long so I had to cut off some of the length and the fit of the knob wasn't great.

$12 for each which gives you 2 feelers (1 right and 1 left). Shipping is $5 USA (regardless of how many). Unfortunately, outside of USA, shipping is really too costly to consider. USPS charges a fortune these days for international shipping. Those of you that know me, knows that I frequently rebuild the M70 and RC-838 boards for members. These are the sliders that I use for spares to replace lost or mangled feeler contacts.

 

[838FAN]

For those pics that show a missing slider contact, are they gone, or were you able to find any rattling around in the slider assembly itself. If you can find any of those contacts, then you would want to put them back in place and use some kind of epoxy like JB Weld to hold the contacts back place works really well.
If you can’t find any of those mini contacts, then good luck finding any part units online. There are people that have spare sliders in contacts, but nobody wants to part with them.
Suppose if it was an extreme emergency, you could get away with putting a couple equal value resistors on the balance Pot so at least you get 50-50 balance without a slider.
For the other sliders it’s a different story. If any of those contacts go out on any of the sliders, then I don’t think you will be able to get any signal through the boom box.
You can test the operation of the slider with a multimeter to make sure both channels are responding with a smooth change in resistance.

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Thank you very much for your answer!!! Is there no chance that the box will work in stereo mode without those contact sliders? I am 99% sure that as soon as I bought it it worked in stereo mode and the white plastic piece where they are glued doesn't really look like there had been another contact slide. I also never found any loose in the cabinet, nor did the controls seem to have ever been opened.if you confirm that I can't really have a stereo signal without having the two contact sliders on the three controls, I am going to try to manufacture them with a small piece of steel wire,at this moment due to isolation all electronics businesses are closed. In the event that it cannot be manufactured, or still does not work, what resistance values ​​do I have to buy and from where to where should I weld it to make it work? (to bypass the sliders) (sorry for so many questions but my electronic knowledge is limited)
Thank you very much!!
Mauro

 

[Superduper]

Uh yeah, OK, good luck with fabricating those tiny feelers.

As for Stereo, this issue with the M70 and 838 sliders has been discussed many times already here. Basically, stereo means TWO independent channels, not 2 speaker. That's why you need TWO separate but parallel circuits, TWO slide rails in the middle of the pot mounted on the resistor board, TWO separate carbon resistor tracks and yes, TWO contact feelers. If they are gone, it's because they fell out of the slot where the shaft travels or someone opened it up, found them loose and removed them.

 

[ELzekio]

Like I said, you could use fixed resistors for the balance and essentially bypass the slider for the balance, but if you are able to, you could buy a couple of the sliders from the gentleman above and just switch out the contact sliders, but use the original resistor board that the sliders make contact with.

Remember, the brown contact board for the balance, base, and treble are all different, so make sure you keep track of which ones went where.