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MAC 4200 - help please

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Projectman

New Member
I picked up a really nice MAC 4200 that has two problems. Overall, it works fine but has two issues I've been unable to figure out
(1) I get sound from both right and left speakers only when I depress the Mono switch. If the Mono switch is out (in the stereo position) only the right side has output. This is true across all inputs (they all work). It's true on all three speaker systems. I can say it didn't used to be this way. I'm not sure when it changed. Now that I've noticed it, I need to figure it out and fix it. Any hints on what to look at? I have the owners manual but I can't get a schematic or service manual on the web. I did contact cleaner on the Mono switch just in case that was dirty but no change.
(2) the tuner has gone nuts. The batteries are new(er) and there is no corrosion around them. The display puts extra or wrong numbers up. Turning the tuner manually is very erratic. Seek doesn't seem to be working. Again, I'm not sure when this started because I usually don't use the tuner but I noticed it when I was trying to trouble shoot issue #1.
 
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Figured it out by myself! I am a bit surprised nobody bothered to push me in the right direction but I thought I'd share the solution in case somebody is searching the archives. I found a service manual download. Using it I found the mono switch on the schematic on the Signal Input section. The switch is on the Tape Switching PC board. It had to be either that board or the Phono Preamp & Electronic Switching PC board. Eliminated the Tape Switching board by switching the L and R inputs. The dead speaker moved from the left to the right so I knew it had to be the other board. Took it out, looked it over and could see no visible defects. The only removable parts are the two RIAA amps. Took them out and reseated them and that solved the issue. Now I'm back to the like new status. Love the sound it makes.
 
Welcome to AK and congratulations on working it out for yourself.
Bear in mind that this forum has a little less traffic than some of the others and weekend posts tend to get slower responses than other times.
 
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