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MAC1900 with Left Channel Problem

Hi when I said I tap on the cage I mean the one that covers the preamp boards . I get cracking in and out sound .
 
kwayde said:
The caps have no affect on what you read when measuring across the balance pot tabs. When you tap on it the wiper may be connecting to part of the resistive pad that's either dirty or compromised.
If you attempt to clean it more I'm guessing more of the resistive pad will be removed and work less than it does now. But since it isn't working you may as well try it and see what happens.
Another thing you could do is pull the pot, take it apart, then look at the wiper and resistive pads to see what's wrong.
When an attempt to clean it makes it worse, it's more than likely ruined and needs to be replaced, but there aren't replacements currently available. That's why I bypassed the balance control for guy whose unit I worked on.
It works fine, you just have no balance control.

Found this thread:
https://audiokarma.org/forums/index.php?threads/mac1900-balance-control-information-needed.756296/

Those two caps are fragile so be careful when around them. The legs break off easily.
Click to expand...
If the legs would break what’s a good replacement.
 
I got both channels to work again but very touchy on the balance knob if I tap on the prongs it cuts out . I wonder if those caps could cause a problem.
 
dmalcom said:
I got both channels to work again but very touchy on the balance knob if I tap on the prongs it cuts out . I wonder if those caps could cause a problem.
Click to expand...
You measured resistance both channels on the pot and found one channel to be wonky. The caps have nothing to do with that.

When you tap on the leads you're moving the wiper on the resistive pads. Something in there isn't right and taking it apart will be the only way to see what's up.
 
kwayde said:
You measured resistance both channels on the pot and found one channel to be wonky. The caps have nothing to do with that.

When you tap on the leads you're moving the wiper on the resistive pads. Something in there isn't right and taking it apart will be the only way to see what's up.
Click to expand...
 

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I took it apart and the and the resistance pad flaked off , I’m assuming the deoxit destroyed it because it worked fine until I cleaned it which now I wish I had not done that.
 
Since these pots are unobtainium and rebuilt ones aren't tracking good, I just bypassed it for the owner so he could use it.

If one ever pops up and you're lucky enough to see it and buy it before everybody else wanting one, then you can replace it.

Bypass it and enjoy the music.
 
Since you have the pot apart you could purchase a pot of same size/form factor, same/similar value, take it apart, and rebuild the original pot with the new wafers from the new pot.
 
dmalcom said:
The reason I ask because one lead fell off . Very brittle.
Click to expand...
No, you need the caps. When I did the bypass one leg broke off too. They are brittle parts. Replace both caps.

See post #3 here: Pay no attention to the last sentence in the post. The caps are .22µf 250v.
https://audiokarma.org/forums/index.php?threads/need-help-with-my-mac-1900-receiver.165938/

To bypass the balance pot take the cap and green wire that were connected to the front balance pot and connect them together.

Do the same to the rear balance pot.

This will take the pot out of the loop and only leave the ground wires. I'd reinstall the balance control and put the other wires back where they belong for the future in case a replacement is found. That way you'll know where everything connects.

Screenshot (661).png
 
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Thanks for your response that’s what I’ll do , I have a couple of sprague 0.22 caps I wonder if they will work fine to replace the original caps.
 
kwayde said:
If you have a meter, check resistance on the balance pot, both channels. That will tell you if the pot isn't working right.

Somebody said that if the pot was already compromised, cleaning it may make it worse. This seems to be what happened to the one given to me to look at.

After I cleaned it again the pot got worse. I'm thinking the resistive pad was already bad and got much worse after cleaning again.

The center taps are the wipers which are connected to the caps.
Put one lead on the center tap and the other on either the green wires or black ground wires.
Slowly work the pot from one end to the other watching for resistance to move in a smooth gradual motion with no drop outs.
Click to expand...
What should the resistance read at middle and at far right or left
 
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