JVC PC-X1000: (Almost) No Left Channel Audio from Speakers or Headphones..Preamp? Or Something Simpler?

[tisaperfectdayelise]

Hello! I just picked up a JVC PC-X1000 for a song ($75) locally. It's in great cosmetic condition, and it had never been opened, until I bought it.
It had a jammed CD magazine, and a loose cassette deck door/cover, and almost no audio from the left channel. I was able to fix the first two issues pretty painlessly.
While I had the back cover off (I used the service manual, so I did everything in the right order), I resoldered the speaker terminal jacks, but that did not solve the issue. I reassembled and tried with headphones...same thing. From the left channel, there is VERY faint audio that remains, even when the volume is all the way down, but otherwise it's almost inaudible and doesn't increase with the volume knob.

Audio logic tells me it's something at the preamp, but to get to the preamp, I have to do some serious deconstruction. Once I do that, I'm should do all the things (replace the belts, clean all the things, typical refurb stuff). I just don't feel like doing all that yet...so...I'm wondering...has anybody come across a simple cause for this very issue with this unit? Some ribbon cable that may be loose to dig for or some pot that (although none of them are scratchy) needs a shot of deoxit? Something that requires less than a complete tear down? The unit is clean, and everything else works flawlessly (to my surprise, even the cassette deck belts are still in good shape...or...at least the decks play well and accurately).

Anyhow, thanks in advance!

 

[hopey]

I like it, the chips they used are not long-term reliable. Its sad but unless you want to find and replace the amps chips you will probable never find the problem.

Just buy another one that works.

 

[tisaperfectdayelise]

I like it, the chips they used are not long-term reliable. Its sad but unless you want to find and replace the amps chips you will probable never find the problem.

Just buy another one that works.

Oh, I'm in the thick of it now I've had the entire thing apart a few times now. Doing this kind of work on an almost-boombox is tedious...I'm used to full sized components, where I can test things in circuit. At least the plastics are still in good shape, which helps me keep calm with the constant disassembly/reassembly .

I couldn't see anything on the preamp board that could be problematic, but that didn't stop me from reflowing every connector point, especially if an L was indicated. I ended up doing that on every board.

No dice. I moved onto the amp board specifically, remembering that the headphone output actually piggybacks off of it.

I swapped the two Toshiba amplifier chips with each other (probably the ones you're speaking of), hoping that I'd gain the left channel and lose the right, but no dice...which suggests to me that the amp chips are still good. I removed and tested all 8 C2785 transistors, the 1317, and the D1302, and they all tested within spec. There are two matching transistors (voltage regulators? Maybe?) attached to the heatsink, and I suspect there's one for each channel? I had to turn in for the night, but I'll remove and test those tomorrow. If they both check out, then there's one more transistor mounted to that heatsink I can test.

The adventure continues! Meanwhile, I found some acrylic sheets that I was able to easily cut and attach to the cassette doors, making it look ALMOST stock again.

Getting another one of these would be great, but this is the first time I've seen one come up in my area in years; and the only one on eBay is pickup-only in...Illinois, I think?

 

[hopey]

Wow hats off too you. I have done the same thing with a few boxes, now stay away from them. There is aways a better box to move onto.

 

[Tinman]

Here's a fix for a similar problem I had years ago.
Click here.

 

[tisaperfectdayelise]

BINGO! It's the volume pot! I got it out, started tearing it down, and out falls one set of the sweepers. The behavior of the stereo makes perfect sense now.

Here's a fix for a similar problem I had years ago.
Click here.

Thank you, @Tinman! I'm used to older equipment, where the electromechanics are simple, and these kinds of things always come down to a faulty transistor or cap. I'm grateful you steered me in the right direction.

I'm having trouble getting to the very innards. I replied @Chris O. 's long dead post, but just in case he doesn't see it, does anybody seeing this one know how get this plastic part off of the post, so I can finish disassembly? Is that black thing on a top a washer/clip? I really don't want to break this...and I'm so stinking close!

 

[goodman]

From the picture, this black thing looks like a washer.
You should try to remove it carefully and still with the necessary effort.
Be patient and good luck.

 

[floyd]

BINGO! It's the volume pot! I got it out, started tearing it down, and out falls one set of the sweepers. The behavior of the stereo makes perfect sense now.


Thank you, @Tinman! I'm used to older equipment, where the electromechanics are simple, and these kinds of things always come down to a faulty transistor or cap. I'm grateful you steered me in the right direction.

I'm having trouble getting to the very innards. I replied @Chris O. 's long dead post, but just in case he doesn't see it, does anybody seeing this one know how get this plastic part off of the post, so I can finish disassembly? Is that black thing on a top a washer/clip? I really don't want to break this...and I'm so stinking close!
View attachment 60912

The black clip is called a starlock push on lock washer. On this case you might have to buy a new washer and maybe try a dremmel tool with a cut off wheel to slowly remove enough metal from the clip for the clip to come off . you have to make not to get things too hot .

 

[tisaperfectdayelise]

SUCCESS! I had to pry that black lock washer off, then the rest pulled right out. Fixed the wiper with some JB Weld (the smaller of the two had fallen off), and everything is working great! I need to take it apart (again! ) - I must have plugged something in backwards or missed a cable, as the CD player wants to stay on all the time now.

Thank you for the help! We saved another one!

 

[Tinman]

You were lucky to find those fingers.
Congrats and enjoy

 

[tisaperfectdayelise]

You were lucky to find those fingers.
Congrats and enjoy

Thank YOU!

That last little blip was, indeed, one little wire of a ribbon cable that I didn't quite get in the hole. I am grateful that those little fingers were still there and were in tact. Now, if the JB Weld can do its job for a very, very long time, I'll be happy

For now, all done! Growing up, this was my grail....now what?

 

[Tinman]

Thank YOU!

View attachment 60914

No problem, glad I could help.
That looks great, nice and clean.

 

[tisaperfectdayelise]

No problem, glad I could help.
That looks great, nice and clean.

I was really shocked by how clean it was, when I picked it up. It was missing the shiny panels on the cassette doors; but that's really common. I bought some black acrylic sheets from Amazon, cut them to size, and double-sided-taped them to where the old panels had been. It's a good enough dupe for me!

The dude I bought this from knew it had the problems it did (as evidenced by both speakers plugged into one channel, and a CD jammed between the magazine and mechanism), and tried to pass it off as flawless; so, there's something particularly satisfying about getting it back to 100% for just the $75 he charged me for it (and a couple of afternoons of putzing around, I suppose).

Thanks again!