MC2105 Low Output on Right Channel

TNTim

New Member
Recently picked up a MC2105. Right channel output and meter is noticeably lower output than the left. Terry can't look at it at the moment so I want to correct the issue with the help of our wonderful group. Soldering is not a problem for me as I use to do it for a living. Unfortunately my troubleshooting skills are weak after not using them for the past 20 years.

Any help would be appreciated.
 
DeOx'ing the meter range switch, if not already done, comes immediately to mind. But if the mismatch is seen on all of the meter range settings, then the meter range switch is probably not the issue.
 
The input switch on the back will cause a channel to drop out if it gets corroded.....Deoxit d5 to the rescue.

The switch adds a capacitor to the input to block DC turn on tumps from vintage preamps.
 
Will Deoxit the switch and meter range switch. Although the audible output level is the same regardless of the settings for the meter.
 
Oh yeah. Anybody know what the last serial # was for these? Mine is BT151* Doesn't match the service manual typical sequence. I assume I need to use the later manual.
 
So finally deOxit all the switches and pots. No difference in the output. The right channel has much lower output than the left. Where should I look next?
 
I am coming in late here, but I assume you switched leads from the preamp, running the right output to the left channel of the amp, right? You also removed the cables from preamp to amp and simply swapped them out against each other right? Finally, you tried another source into your preamp right, i.e. if the CD player was the original source, try the TV or tuner, etc. To me before assuming something is going on in a unit, best to eliminate stuff that might be on the outside.
 
A quick update.

I was able to feed a sine wave into the amp through an iPhone app. Measuring with an O-scope at the beginning of the input stage both channel sine waves are the same. At the end of the input stage, they are different. The right channel is almost half the size. From this I assume something on the input stage is causing the drop on the right channel. The electrolytic caps are all original so I am going to replace those. Could it be C9 or C10 causing this? Should I be concerned about any transistors on the input board?
 
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