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Pioneer sx-2000 mode switch

only thing that seems likely to mess with the frequency response are the components in the feedback network.
 
Yeah all the tubes have been tested and even swapped and the problem still stayed with the same side. What area of the circuit is responsible for the feedback network?
 
I'm still stuck on the phono section: Do you have a cap tester? I'm thinking one of the new replacement caps are bad, that you replaced, that comes out of the phono section to the main.
 
Alright so here's a little update. I went ahead and changed a few more out of spec and resistors and caps that are connected to the 12ax7 right before the phono section. It's getting closer but still a little less dynamic on the left channel. Sound output is closer but the right channel definitely sounds better and more dynamic. When I was testing it I noticed that it's actually on all inputs just much more noticeable on the phono input. When I was testing it I had lost the left channel initially but after cleaning the volume pot again it came back. I wonder if this one just had a shot volume pot and that's why there's a difference in the channels
 
possible, is the balance off channel to channel? Thats usually how volume pots get funny, the tracks drift relative to one another. Extra annoying is when they don't drift consistently across the range and the balance shifts left to right as you turn it up.

can also ohm check the pots end to end. If its more than about 20% off, that may be an issue.

also consider the tone control pots will have the same possible issue, as will the components in the tone control circuitry. Might be worth some channel to channel checks just to see if things measure about the same.
 
Yeah the imbalance is consistent no matter where the volume pot is set. The check the volume pot would I need to remove it from the circuit or would it be ok to check while still hooked up? I didn't think about the tone control pots but since the volume is close just deeper on one side that would make since. I've got time to dig around and experiment today so hopefully I get it figured out finally!
 
I checked the volume pot in circuit. I connected my negative lead to the tab on the left if looking at the pot from the back and connected my positive lead to the center terminal.
The front half readings are: volume set to 0: 253k, turned up halfway 320k, 3/4 195k, and full volume 482ohms

The back half of the pot reads: volume at 0 330k, halfway 350k, 3/4 165k, and full 5k

Not positive if I took the readings correctly tho
 
ground to the center wiper should be fine. It doesn't matter all that much which you do, so long as you do the same thing on both sections. The fact that it doesn't track the same tells me something isn't real happy. To figure out of its the pot or stuff around it you'd probably have to unhook the wiper and check it again. Also looks like there is a second control just after it. Is that a variable loudness ? Looking at VR1 and VR2 on the schematic.

unless VR1 is balance and VR2 is volume.


something worth checking, if that is a variable loudness and there is a loud-off switch (S4), make sure both sections of that are working properly. If the loudness is on in one channel but not the other it will make it sound thin on one side.
 
Yeah that's a good idea. I'd hate to order anything else for this thing and I still have problems. The volume pot has a loudness tap that connects to a loudness switch directly below it. I'm heading out on lunch but when I get back I'll desolder the wiper tab for the pot and double check that it still shows the same issue out of circuit. How would I test the loudness switch itself? I've never had to do that before
 
looks like its just a simple on/on switch so a continuity check ought to do it. Not sure the physical arrangement but it should have a common terminal, 0 ohms from common to one end in off, 0 ohms from common to the other end when on. Guessing it will be a double row of 3 terminals, center is probably the common and either end will be the open and closed contacts. Top row is usually one channel, bottom row is the other.

Check the caps attached to it too.
 
Alright so after removing the volume pot and testing it with all the connections removed it's actually really close on both sides so I no longer think that's the problem. I worked my way back from there down to the loudness switch and the components connected to that. Both sets of caps test as almost identical matches so that can't be the problem. There are 2 resistors coming from the loudness tap that connects to a tag strip near the balance pot. Those resistors measure 14k and 12.5 k. Do you think that would be a far enough difference to cause this problem? The resistors in question should be 15k.
 
The loudness switch isnt dead, I can tell a difference with it being on or off on both channels so I don't think the switch itself is the issue
 
One more update for today, I didn't have time to fully remove the balance pot but I tested it with everything from the volume pot and loudness switch disconnected and I did a sweep resistance reading and on the rear pot I get 445k-125k and the front pot I get 340k-73ohm. When I have time either later this week or early next week I'm going to reconnect the volume and loudness switches before I go any further so I don't mix up how the hook up and then remove the balance pot completely and test it again. It doesn't help that my grabber leads broke earlier and now I'm just using the test probes that came with my meter haha
 
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Wait I forgot to mention on the volume pot, when I did my testing with it fully disconnected, when turned all the way to full volume the front reads 9kohm and the rear reads 390 ohm. Everywhere else is within 3k ohm until the very end. That wouldn't cause a problem unless the volume was turned up all the way, right?
 
seems like that would be the case. Probably worn or possibly damaged right at the end but if its pretty close in the range where you normally have it, I wouldn't worry about it.

Not sure on the fixed resistors but different channel to channel, but I'd be more inclined to think its something connected to them making them read odd. I've never personally had a resistor drift low in value. I suppose it could happen but normally when they read low in circuit, its because of the circuit.
 
Yeah that makes sense, I don't see myself cranking this to max volume and if I do I don't think I'll be sober enough to worry about the imbalance haha
On the resistors I disconnected them from the loudness switch and just left the other ends Tied together on the tag strip and measured each one that way. They are both within the 20% tolerance but the low one is right on the edge. I think for piece of mind I'll go ahead and replace them and test the balance pot out of circuit while I'm there
 
Eureka! I finally had time today to get the loudness switch and volume pot reconnected. From there I removed the balance pot and tested it. When I tested the pot it seems to be defective. Assuming it should operate the same way as the volume pot it showing pretty large differences between front and back side of the pot. At the highest resistance point I get around 700k ohms and 1100k oh. On the other side. That plus the 2 resistors being so far apart I think is the case of my issue. Going to replace the 2 15k resistors and the balance pot and in hoping that will solve my problem. Does it sound like I'm on the right track to you gadget?
 
700k vs 1100k would cause you some troubles. Whats it supposed to be?

If you can't find a reasonable match for the balance pot you can probably fake it with some fixed resistors to bring it back on value in the center at least.
 
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