jvc rc-838 switch problems

ok i'm working on an 838 for autobot , the power only comes on when i press the buttons on the deck , cannot turn on tuner with power switch but you can turn the power off to the tuner when the tape is playing using power switch , wtf ?

i replaced the power switch with a unit supplied with the radio + no change wtf?

you can switch from tape top radio but only while the tape mech is engaged .

next the balance control does nothing and both speakers play through the left side even though nothing has been altered wtf ?

basically the vu meter on the left works as it should but the right side only works in bi phonic mode wtf?

everything inside looks great with no signs of butchery or fiddling around and i'm pretty sure this box has never been opened after fighting with the back case for 12 rounds i finally got the sumbitch off.
any idea's ?

Do you have a voltage meter that can read DC? First check if you have dc voltage on one side of the power switch
( the line side ) with radio plugged into an AC outlet. BTW, does the 838 have one of those sleep switches?

it has a position on the power switch that say's off/sleep.

got my fingers crossed you can get the bugs worked out

That is a clean 838, so hopefully you can get the bugs worked out. I had no idea it would be such a handful that some simple switch cleaning wouldn't clear up......

JVC Floyd said:

next the balance control does nothing and both speakers play through the left side even though nothing has been altered wtf ?

basically the vu meter on the left works as it should but the right side only works in bi phonic mode wtf?

Click to expand...

If this is similar in its colour codes to the 656, then it'll be exactly the same cause as I just found in a 656 that I just bought for parts and found to be too good to break as the transport and a/f chips are perfect.

Whoever had been in about at the set had managed to get the supply for the VU meters (handed, but coupled into one sweep for both channels on the 656 as it's easier with its LEDs than with ballistic meters such as these on an 838, thereafter the circuit looks the same) mixed about with the supply for the +ive side of the voice coils on the "dead" channel.
The clue was that the meter, although coupled on the 656, only gave a reading on the affected channel when its supply was disconnected and measured upstream of the bridge that couples the outputs for the single meter and then only with the volume well up.
Possibly, the same tired or just unlucky phantom repairer has been in about at your 838? This would have been easier to find with separate meters as you have there, because the symptom was more obvious than in the later, less complex set with its coupled meter feeds.

i'm pretty sure the balance problem is related to signal input/output because the headphone jack also only plays on the left side but plays both sides in bi phonic mode .but the balance control does nothing .

Yes, that is in line with my findings as detailed above. Try swapping the feed for the meter on the affected channel with the one that's connected to the speaker +ive, it will do no harm and the route is easy to trace visually.
A forum member who wishes to stay anonymous has just told me that he's had the same reversal of these connections in a Hitachi set whose "wide" mode works in exactly the same way as JVC's Biphonic to render binaural material.

Seems to me the output issue is due to a dead channel. It works in biphonic because that mode bleeds a signal from the opposite channel into the dead channel thereby appearing to "revive" it. Wide and Biphonic modes mixes the L and R signals together with a time delay introduced. Now whether the dead channel is due to a dead B or T slider, or whether it's due to a faulty section of the preamplifier section, or whether it's something as simple as a cleaning issue... I cannot say. As for the power issue -- you'll need to do some troubleshooting with a meter to find out about that. Most boomboxes utilize a parallel power system where the tape and power switches are powered up separately. It "sounds" like the tape section is getting power but not the power switched section.

[SIZE=10.5pt]I had similar problems with my 838. A good switch cleaning fixed all the issues. [/SIZE]
[SIZE=10.5pt]Some of the switches are all hidden inside and they are connected by levers. Initial cleaning showed some improvement which gave lots of hope for a very vigorous cleanup.[/SIZE]


[SIZE=10.5pt]As you know 838 is a very old guy, it is the grandpa of stereo boomboxes. [/SIZE] Those contacts will be badly oxidized depending on the environment.

sounds like i need somebody smarter than me to fix it lol. the repairs are no problem , it's the diagnosing the problem that sucks .thanks for the suggestions .

Royce could be right. Some boxes have the dual power switches. One regular and a micro switch triggered by arm. Most likely it's the micro type switch that is very difficult to clean inside, sometimes needing removal to clean real good. I've ran into 2 units like this, Sanyo M X720 and the Hitachi I just finished for member


Bad Boy Bill

You need to check the contacts of the inside plugs which connect the boards. I had a similar problem with my 838, and I found that the "pitchfork" contacts inside the plastic housing of the plug was corroded and it performed a bad contact with the board pins. You may check this with some gently pulling the wires from the plug or the plug themselves.
In the pic below is the plug which I have found that is with corroded contacts.



good luck

devol-toni said:

You need to check the contacts of the inside plugs which connect the boards. I had a similar problem with my 838, and I found that the "pitchfork" contacts inside the plastic housing of the plug was corroded and it performed a bad contact with the board pins. You may check this with some gently pulling the wires from the plug or the plug themselves.
In the pic below is the plug which I have found that is with corroded contacts.

jvc 838 contact.jpg

good luck

Click to expand...

I had a similar problem with my C-100 when I got it. The left channel would go berzerk when I'd turn up the volume, until it finally stopped working. I've gotten a lot better at this silliness we refer to as "Boomboxery" since then.
https://boomboxery.com/forum/index.php?/topic/14369-left-channel-in-and-out/?hl=%2Bleft+%2Bchannel+%2Band+%2Bout

ok fellas i'll give it a try and see what happens .

thank you .

i opened her up and messed with those connectors = no luck , they were kinda loose but not enough to affect anything because i messed with them while it was powered up just too see if anything changed when i started pulling on the wires.

thats it time for the sledgehammer

Patience! Have more patience!

Do a very vigorous switch cleaning one more time. Work at least 50 times after deoxit treatment.

it's a sweet box but damn those gremlins drive you bonkers.

oh trust me i wish i could submerge the whole box in deoxit and be done lol.
not that i'm in a hurry , just want it to work right .