MX110 Right Channel Out

DrRobocop

New Member
Hello all,

Long time lurker, first time poster.

I'm seeking some guidance regarding my MX110's non functioning right channel. Thanks to all helpful contributors and wonderful info on this site, I took it upon myself to repair my newly acquired MX110 after a local tech made a real mess of repairing the power supply.

I am a complete amateur, but, with the collective wisdom of this site's contributors, I have been successful in re-caping the unit, and replacing the power supply on this MX110 as well as 2 other MC240s.
The unit was functioning well after my initial repair, but I couldn't leave well enough alone. I recently swapped the 1uf capacitors and surrounding resistors at the front of the unit (the ones related to the tone control's I believe). Since then the right channel has stopped producing sound.

Things I have tried:
  • I went back and have cleaned up and re-soldered all the connections
  • tried different caps and resistors
  • cleaned all the switches with deoxit
  • used various settings on the mode selector
  • swapped the 6u8 tubes.
  • The problem also occurs when I use the tape monitor outputs.
Any ideas?

Thanks in advance for your help!
 
A signal tracer would help you very quickly determine where the problem lies. They're not too difficult to build ...
 
A signal tracer would help you very quickly determine where the problem lies. They're not too difficult to build ...

Thanks for your reply! I'll look around online to see about building and using a signal tracer. Would you recommend any first steps I could take with my multimeter?

I'm hoping the problem is an easy fix (a wire without enough solder, wrong connection, etc..). Once troubleshooting goes beyond the more obvious stuff, I'm a bit lost.
A little bit of knowledge can really get you in trouble...I've had success so far, but I hope I didn't wade in too deep and mess something up that I am completely unaware of.
 
Thanks for your reply! I'll look around online to see about building and using a signal tracer. Would you recommend any first steps I could take with my multimeter?

I'm hoping the problem is an easy fix (a wire without enough solder, wrong connection, etc..). Once troubleshooting goes beyond the more obvious stuff, I'm a bit lost.
A little bit of knowledge can really get you in trouble...I've had success so far, but I hope I didn't wade in too deep and mess something up that I am completely unaware of.
You could inject a 1kHz test tone into the inputs and follow the circuit with your DMM, comparing voltages from one channel to the other. A copy of the service manual would be handy.
 
You could inject a 1kHz test tone into the inputs and follow the circuit with your DMM, comparing voltages from one channel to the other. A copy of the service manual would be handy.

thanks for the suggestion! That seems like something I could probably perform. I do have a copy of the service manual, so I'll give it a shot this weekend and let you know how it goes.
 
I'd go back in and look at the area where you replaced the (2) 1uf @ 150volt electrolytics (with film caps I hope). They are in the audio circuit so maybe you have a cold solder joint or broken lead there(?). When I replaced those two caps in my MX110 two years ago I found it an incredibly tight spot to work in plus two resistors were taking up some real estate, too. Just a thought since you do mention until you did that, the unit worked okay.
 
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I'd go back in and look at the area where you replaced the (2) 1uf @ 150volt electrolytics (with film caps I hope). They are in the audio circuit so maybe you have a cold solder joint or broken lead there(?). When I replaced those two caps in my MX110 two years ago I found it an incredibly tight spot to work in plus two resistors were taking up some real estate, too. Just a thought since you do mention until you did that, the unit worked okay.

Thanks for your reply. I'm going to try that again first. That area is incredibly crowded, as you noted, and it's easy leave a bad connection in there. This all started when I replaced all the resistors and caps in that region with NOS allen bradleys and a set of arizona blue cactus capacitors. Those were way to large for the area and I never felt great about how I wedged them in there, or for the sound they provided. So I switched to smaller auricaps. The problem occurred after I switched to the auricaps, I may have left a cold joint, but I doubt it...I've gone over the area a few times, since then. However that is my first step this weekend.
 
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