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Pioneer sx-2000 mode switch

Looks like the left channel is out on the tape monitor input too. Any suggestions on what area I should look in?
 
So it looks like I'm looking for a section of the circuit that the phono section, tape hd, and tape monitor all pass through but the aux input does not. Wish I could make better sense of this schematic
 
so just to confirm, you have left channel in tuner mode and in aux, but not in tape head, phono, or tape monitor correct? Setting it to mono also doesn't make it work? Just want to be sure I understand clearly here.

just gonna say that doesn't make any sense. The signal from the aux jacks flows through the input selector to the tape monitor switch, then to the mode selector. I can't think of a reason why aux would work but the tape monitor would not.

also just to be clear, tape monitor is not tape head. Different thing completely.

Try setting the stereo/mono left / mono right to either mono left or mono right and let me know if you get sound from both speakers in either mode.

something else specific to check on the left channel is the phase reverse switch. I've had a lot of issues with those. Quick and easy way to eliminate it as a possible issue is to plug in a set of headphones. If both channels work on the cans but not on the speakers, there is signal making it all the way through the amp, but not to the speaker jack. Only thing between the amp output and the speaker jack is the speaker switch, impedance switch, plus the phase switch on the left side only.
 
Yeah, both channels work on aux, tuner, and tape monitor inputs. My initial test only gave me the right channel on tape monitor but it's possible one of my cables were loose or something. Only right channel on either phono input and tape h.d.

With phono input selected I cycled through the stereo mono switch and here's the results:
Stereo: only sound on right channel
Mono left: sound is very low on the right channel and nothing on the left
Mono right: sound output is normal on the right channel but still nothing on the left
I repeated the experiment with headphones and got the same results
 
that still doesn't really make much sense. Normal function on the line level inputs tells me its something specific to the phono stage, but I'd expect both channels to play normally when using the mono right position on the switch. That switch is after the tape monitor switch, so if signal is coming through normally on the right channel, it should simply pass that signal to the left channel amplifier. Either way, if the left channel plays with the tuner, aux, and tape monitor set in stereo mode, we know that everything after the input and mode selector must be working.

anyway, phono and tape head go through V1 on the left channel and V2 on the right. None of the other inputs route through that, so I'll say the issue is somewhere in that area. How does the plate voltages on V1 compare to V2 ? pins 1 and 6 would be the ones of main concern here. If those are fairly close, find the two 0.1uf caps connected to pin 1 of those tubes. Jumper the not-plate ends of those caps together and see if you get signal from both channels.
 
Sorry to take so long getting back, I had organized a concert this weekend and was really busy. At any rate, I'll have time Tuesday to dig back in to this and hopefully get it solved. Thanks for the advice gadget!
 
I'm finally having time to sit down with this and get some readings. Here are the results:
V1: pin1 (-.2v)
Pin6 0
V2: pin1 90v
Pin2 89.5v

Also the .1uf caps are connected to pin2 and pin6 on both sockets, not pin1 and pin6. That's how it was when it came to me I beilieve
 
I take that back on the location of the .1uf cap, it's actually on pin1 where it's supposed to be. Here's a couple pics
PXL_20220809_174330547.jpg PXL_20220809_174326011.jpg PXL_20220809_174315125.jpg
 
Oh I think I found something, the 100k Suzuki dog bone resistor on pin1 is reading open, let's see if I have a replacement handy...
 
that'll do it. When I saw no plate volts I was going to say check the resistors that feed to that tube. That style of resistor sometimes has the end cap break loose from the carbon spiral on the tube and it goes open circuit.
 
You must be rubbing off on me! That was my first thought as well. And low and behold there's a dead resistor! I just changed it out, have a customer in my shop now but as soon as they leave I'm going to fire it up and test the voltages, wish me luck!
 
Alright just posting an update for future researchers. After replacing the dead resistor I found that one channel was quite a bit quieter than the other but only on phono. I measured all of the dogbone resistors in the phono circuit and found most were pretty far off from eachother. I ordered all new carbon film resistors for the phono section and they arrived today! I'll replace them tomorrow and report back but I'm 99% sure this is going to solve my problem. Thanks for all your help gadget, I couldn't have done it without ya!
 
Odd they drifted. I've had fairly good luck with those things staying on value, other than the ones that have randomly gone open circuit.
 
I'm not sure if they drifted exactly, most were within 20% but one I'm particular was around 20% over the rated value on the right channel and around 20% under on the left channel. The difference is noticable but if I turn the balance knob a little to left it balances out. May have came like that from the factory but I figured I'd make it sound as good as possible since I've already put so much work into this one. I'm going to swap those out in a few hours and see how it goes
 
I like parts to match channel to channel as closely as practical. I'm not really a big believer in a lot of audio woo but it just seems obvious to me that different value parts side to side have to produce different results. Off-value resistors, depending where they are, can definitely affect gain in a stage.
 
Same here. I don't usually get too crazy with it but when restoring a piece I'll typically test a few of the more critical resistors and if they are close I'll leave them alone. If more than 1 or 2 are off then I'll test alot more and go from there
 
I changed out almost all of the resistors in the phono section and unfortunately the imbalance is still there, although it is better than before. It just seems like the right speaker sounds more full with more bass if that makes sense. If I turn the balance knob just a bit to left if balances out so it's not an extreme difference but enough to notice, especially if i go back and forth between only left and only right on the balance knob. I think this is good enough though and will probably call it a day on this project so I can get to working on some other stuff. The balance problem is only on phono btw and I have swapped the phono tubes and the imbalance stayed the same
 
if the resistors all match and the tubes don't move the problem there isn't a whole lot left. An 0.1uf as the output coupling cap on each channel and an 0.01 between the sections. There is also the feedback stuff, but that would mess with the top end more than the bottom. Could produce extra boost though, and its not so much a lack of bass, but an excess of treble.

should be R15, R17, C5, C7 I think? Hard to make out, and its got both the tape and RIAA eq stuff sort of merged together. Its the group of stuff connected between the selector switch and the first triode's cathode resistor. RIAA will be the two resistors with a cap across each. The single resistor with a cap across is the tape head eq.
 
I've changed both the coupling caps, I'll check r15 and r17 when I get back to the unit tomorrow. I believe I did the .01 as well. I'll take a few pictures of the phono section while I'm in there tomorrow and see what you think
 
Alright so I've had a busy past few weeks but finally had time to mess with this. I went ahead and changed every component connected to the 2 12ax7 tubes in the phono section. Unfortunately the imbalance is still there. It sounds like there's no midrange in the right channel. It sounds really tinny. I've swapped tubes, and speakers and it always stays on the right. Here's some pics but at this point I'm all out of ideas.
PXL_20220830_204200685.jpg
 
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