Mcintosh 1900 receiver issue

RS Steve

RS Steve

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I have a real nice Mac 1900 receiver, it works great except for the phono stage. It only plays out of one channel on either phono 1 or phono 2. It has had a complete deox of all the controls, and nothing obvious is present to show something went bad. I thought someone with knowlege on this model might have an idea to what would cause this. Thanks!
 
Pull the preamp cards and clean the card contacts with an eraser. At some point you will need to swap the cards L for R, to confirm the problem switches channels. If so a bad transistor would be a likely suspect.
 
c_dk said:
Pull the preamp cards and clean the card contacts with an eraser. At some point you will need to swap the cards L for R, to confirm the problem switches channels. If so a bad transistor would be a likely suspect.
Click to expand...

Ok, thanks for the information, I will try that today. The problem is in the phono section only.
 
Switched the boards around, and the dead channel stays with the right side phono. I do notice on FM that the right channel is weaker than the left by a little but not dead as the phono is. Playing in mono, both channels play, even the phono. I will deox all jacks again to make sure that isn't the problem.
 
You switched the preamp boards, lh front? There is not a whole lot in common between ph1&2 before these boards......
 
I have cleaned and deoxed all jacks, and pots again, switched preamp boards, and switched amp boards but the right channel will not work on phono, and is weaker on all other sources. I am lost as to what's wrong. :sigh:
 
Time to check continuity.....could be bad ground from RCA jacks to switch to preamp boards etc.etc.etc.
 
c_dk said:
Remember the connections from the rear section of the input switch to the eq board.
Click to expand...

It looks like I am getting conductivity to ground on the inside of the RCA jacks for the right channel at all times, where the left side I get no signal until the selector switch is in the opposite phono stage. If that makes any sense. :scratch2:
 
So any input in RH is shunted to ground all the time...........and the functioning phono input shunts to ground when not used, making it quiet when switching past it.
 
c_dk said:
So any input in RH is shunted to ground all the time...........and the functioning phono input shunts to ground when not used, making it quiet when switching past it.
Click to expand...

Yeah, that's the way I see it. Since the right channel does not work in either phono setting, I imagine there must be an issue with the right positive section, since it shows grounded at all settings. But I'm not very electronics savey.
 
Are the "pinchers" bent in the selector switch. I have seen them corrosion freeze to the selector surface and then get bent when rotated.
 
c_dk said:
Are the "pinchers" bent in the selector switch. I have seen them corrosion freeze to the selector surface and then get bent when rotated.
Click to expand...

They all look to be ok, I see them move up and down slightly when turning the knob.
 
This receiver is driving me crazy, I can't seem to nail down the cause of thr problem, I have done about as much as I know how to with no improvement.
 
Well, just fixed the problem, turns out all I needed to do was tighten all the screws on the back of the receiver. I guess it was a bad ground issue, and the problem is gone. I have to say I'm very happy about it, now the 1900 is working perfectly. :thmbsp:
 
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