TC-D5 Very low volume on left channel

Hi all,

Last week I got a cheap TC-D5 in the mail listed as broken. Turns out the belt for play just dried up and after replacing it I found some other problems.
The potentiometer for 'monitor' level was not working properly but a cleaning fixed it. Despite also cleaning the headphone jack with 99% alcohol I can only get one channel to work properly.

Looking around on the intetnet didn't give me much solutions, I did clean the rec/playback switch and the head with 99% alcohol after and now the left channel is there but just very low. The VU meter also doesn't do anything, only on the right channel.

On line output I do have left and right on my headphones. When I take my adapter out of the headphone socket it switches to the left channel only and fiddling around with it sometimes give me audio on both channels.
It leaves me wondering if my 6.3 to 3.5mm adapter just isn't compatible or if there's another way to clean the headphone socket?

 

Thanks for the link, I've checked the wires but they're all good and all have good continuity from connector to PCB.
Maybe a stupid question but are all of these supposed to give continuity to ground? I checked with my multimeter and then with my continuity meter because I saw that the pins were connected through resistors. My continuity meter gives continuity at under 40 ohms only
Should I just keep trying to clean it or could there be something else?

 

I suggest to start by looking at the block diagram signal path. From my understanding you said that the line out is fine, but you have no left channel on headphones out and no VU-meter movement.
If we look at the block digram of TC-D5M (don't have the manual for D5 but should be very similar), we can see the line out is taken directly from the CX174 Dolby IC. So that we know to be good.
After that we have the Q105 buffer amplifier which drives both the VU-meter circuit and the headphones out. I would look in that area, especially cold solder joints on the small PCB near the speaker.

In regard to the continuity test, you need to measure the actual resistance. Below 40 ohms does not mean a short circuit.
The outputs have some load resistors, on the D5M they're 100 ohm, so some resistance is normal to be there. Question is how low it is.

 

Small update
Thanks for the help and schematic!

No luck yet sadly, Q105 looks fine and so do the surrounding components
I did reflow the wires to the headphone jack just in case but no difference. I noticed the unused connectors of the jack plug are partially oxidized (black)
I think the next step is to open it back up again, maybe clean the req/playback switch with something else than 99% alcohol and reflow everything connected to Q105
I'll also measure the resistors just to be sure

 

@SoundBuzz
The fact Q105 looks fine visually doesn't mean much. You need to check the signal path from point to point (with oscilloscope or multimeter):
- is there signal at the base of Q105 ? What about the emitter ? Compare to Q205: is the signal level similar ?
- after Q105 you have the volume potentiometer, do you have signal at the cursor ? Compare L with R: are they similar ?
- after the potentiometer signal goes through R451 & C437 straight into pin 2 of the headphone amp (IC402, IC502). Do you have signal here ?
- output of headphone amps are at pin 3: do you have signal here ?

If you don't have a scope, feed the line in with a sinewave (can be from a DAP, computer), put the unit in record mode and measure the AC voltage with a multimeter.
The REC/PB switch I do recommend cleaning with Kontakt 60, this is something that should be done as preventive maintenance anyway.

 

I was hoping to find cracked or loose solder joints but it's sadly not this obvious. I do have a pocket multimeter but I contacted a friend with a scope and more tools so we will check all these points and I'll post an update afterwards. Thanks in advance for the detailed help! I'll also order a can of Kontakt 60 soon