JVC 838

Status
Not open for further replies.

Mainframe562

Member (SA)
Jul 28, 2010
64
0
6
Southern California
Well i purchased yet another box and this time its a JVC 838. Problem i am having is that there is no sound coming out and while cleaning the balance switch, a metal piece came out. Not sure what the correct term is but has 3 legs and maybe what is needed to fade the balance from right to left. My question is, could this be the problem why no sound is coming out?
 

Superduper

Member (SA)
That is EXACTLY why you are getting no sound, and will require major surgery to fix. That balance slider is an obsolete part and will require creative sacrifice of similar NOS sliders to fix. The part you found are the feelers that bridge two sliding connections. That is a stereo control so that means there is one more feeler in there, and since you aren't getting sound out of either channel, it might be lost.
 

Mainframe562

Member (SA)
Jul 28, 2010
64
0
6
Southern California
Thanks Super, is there maybe a way to modify the board so that the balance slider is set to the middle? Hopefully there's a way, would hate to see a good box go to waste.
 

Superduper

Member (SA)
Yes, it might be possible to modify the board with fixed resistors instead. But the curve might not be linear so the slider will need to be disassembled to determine what the values should be when the slider is in the middle position anyhow. You should know that the other sliders (bass/treble/record-levelsX2) are similarly constructed and probably not far behind. OR they might already be bad too, The design of this boombox is such that a bad bass or treble slider (they are both stereo controls as well) will also cut the sound to that channel. On most others, a bad bass slider translates to non-adjustable bass. On this one, it transalates to no-audio-signal pass through. Of course there might also be an issue with the power amps as well but first things first, I know for a fact that a balance slider missing it's feelers will result in no audio in the channel with the lost feelers. Just trying to tell you from experience that it's not uncommon for multiple issues to exist and with NO audio right now, there is no way to know for sure until you resolve it one issue at a time.

But before you go any further, you need to determine if the preamp is working properly. See if the boombox will output a normal signal from the line-out jacks which is fore of the tonal controls. If yes, then I'm pretty sure the issue is in that tonal board.
 

Mainframe562

Member (SA)
Jul 28, 2010
64
0
6
Southern California
Well when i unboxed the bbx and turned it on, there was a faint sound coming out of one speaker but when touching any slider, the sound would become louder. So i thought maybe cleaning the switches would fix everything but when that feeler came off, there was no more sound. You are correct in that if one slider is damaged it may effect the output of sound from either channel, in this case the balance slider went out therefore no more sound. May have to open the switch and examine it. I still have the feeler and upon looking at it, looks to be intact. I will see if i can revive this switch.
 

monchito

Member (SA)
May 5, 2009
4,601
6
38
pythonville florida
mainframe most of the time when that happens its because it broke if you are lucky and are able to open it up and try to replace the slider ,, and another thing on most of these older jvc boxes which uses sliders they tend to go bad often ,, i have a 828 which works but is in need of the bass slider also , mine use to work but i went to try it and it stopped working so basicly it stayed like the in between sound.. :-/
 

Superduper

Member (SA)
Those sliders are obsolete. Trust me, I spent many days, weeks, months looking for some to replace the ones on my restored 838. I spoke with a JVC representative who confirmed that the part is no longer available. While other similar looking sliders can be purchased, they won't work properly because the ones, especially on the BASS/TREBLE has a very unique resistor response curve. You MUST rebuild that control and if any feelers are missing, you must sacrifice some from another NOS slider which won't have the same tone curve. I have rebuilt many of these, on both the 838 as well as the M70. The sharp GF-9494/9696 has the same issue.
 

Mainframe562

Member (SA)
Jul 28, 2010
64
0
6
Southern California
From the looks of the slider, its pretty bruised and battered. The plastic piece holding the feeler down is missing so not sure how to keep that on there. Gonna have to insert a fixed resistor but does anyone know what resistor value? The slider is a 20k ohm so do i install a 10k resistor so that it stays in the middle?
 

Superduper

Member (SA)
Mainframe562 said:
From the looks of the slider, its pretty bruised and battered. The plastic piece holding the feeler down is missing so not sure how to keep that on there. Gonna have to insert a fixed resistor but does anyone know what resistor value? The slider is a 20k ohm so do i install a 10k resistor so that it stays in the middle?
That's what I'm saying. In the middle, it's not like that. It could be 20k total and maybe 3k in the middle. Anyhow, you don't need to remove/install a resistor, I don't think. :hmmm:

The feeler merely bridges the track and resistor. The resistor should have a center tie down point. Merely bridging the track and center pin of resistor should amount to the same thing. Of course you'll have to do that for both sides.
 

Mainframe562

Member (SA)
Jul 28, 2010
64
0
6
Southern California
Well i rebuilt the balance and upon testing with an ohm meter, the resistance value does change. So im good there but when desoldering and checking the bass and treble, they both were missing 1 feeler, so leaves me with one step forward and 2 steps back. :sad: I was hoping i can find a NOS slider and use the feelers in there but not sure if the feelers are similar. If i cant figure this out then i will have to wait for someone to sell a parts box or im just gonna sell it. :'-(
 
Status
Not open for further replies.