Only one speaker works on TRC-931

I just bought this vintage boombox at a flea market here. Got very lucky with the price it looks like a hack tech has already gone through it with his golden screw driver. The original volume potentionmeter has been replaced with an adapted one and there are a few other issues with it as well. The replaced pot is 50k and I don't know if that's the original value called for.

I need help locating a schematic for it.

The main issue with this thing now after some work is that I only have audio on the right side speaker.

All help is appreciated!

The 50K sounds about right, good luck finding a scheme you may want to try plugging in headphones to see if you get signal to both right and left...also you can try to deoxit the controls. But you need to open box and do this from inside good luck

Hmm so I suppose finding schematics for these is a pretty difficult thing to do eh? Does anyone know if they where ever put under sams photofact? I guess I'll try and have a look at that.

It still looks like it may have some other issues such as the tape deck but I'll get to that once I have this bigger issue done with. At first I had very low audio but re doing solder joints seems to have solved that.

Thanks for the help!

So Sams photofact does not have the schematic either and it looks like no one does. Oh well!

Here is my progress so far, hopefully some of this information will at least be helpful for someone else around here searching for a fix.

After finding out Pin 6 of the TA7270P is the input for this amplifier IC I touched it with my finger on IC504 which is the left channel IC amp on this board and heard loud powerful buzzing from the left speaker which is dead and our problem speaker.

I can only assume from this that the IC and the amplifier stage in general is in working condition here and is just not receiving an input signal. It appears TR502 is it's driver transistor, it is a 2SC1815. I tested it but it appears my multimeter is crapping out so I did not trust the bad reading and instead replaced it anyway with a proper close equivalent 2SC945. However all remains the same.

Furthermore I wouid like to point out that my balance control seems to be unresponsive, I would assume turning it all the way to the left where the problem lies would make the right speaker at least reduce in volume. However it does not seem to do a thing. When I touch the right side pin (front view) of the potentionmeter I get the same loud buzzing from the left channel. I get a slight hum on the right channel when I touch the left side of the pot.

Anyone have any more ideas of where to snoop around?

I found an interesting detail now. After what I said about the balance control in my previous post I decided to just bite the bullet and take it out for testing. My multimeter seems to be working again so I had nothing stopping me now.

Turns out the left side pin (front view) is open. The right pin, sweeper, and center tap read correctly. Yes I did say center tap, which has me worried about finding a replacement.

Furthermore I still feel that the symptoms I'm having with this boombox don't all quite match up to the defects of this bad pot.

AH PROBLEM FOUND

It turns out it is the dual gang center tapped volume pot. If it weren't for my crappy multimeter I could have saved myself a lot of head scratching but I eventually found my way back to it. Haha. After I was about ready to quit for the day, I just said what the heck and grabbed a spare 50k pot I had lying around and touched it to the pins of the secondar section of the dual pot volume control and sure enough the left channel started kicking!

Since center tapped pots are probably next to impossible to find now I wil be replacing it and the tone control with standard dual gang pots. Currently I have it replaced with two seperate 50k ohm pots for testing and it works great.

Well there ya have it!

Once I get the proper replacement parts and get it back together I'll post some video and pictures of it.

-Carlos