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MC2205 - Left Channel Intermittently Has No Signal / Strange Behavior

Caesar Swift

Caesar Swift

New Member
I've been somewhat obsessed with great quality audio and gear as long as I can remember. Recently acquired the incredible MC2205 after the passing of my wife's grandfather along with a C28. These two sat in the same place in a house for ~ 35 years and we would play all sorts of genres on vinyl together. Never had any issues.

My dad and I went over the 2205 thoroughly - checking all connections, Deoxit, general cleaning up, etc. Many suggestions of which we discovered in this community. I'm having an issue in consistently getting the left channel to recognize an input signal. It works one minute and then not (more on that later on). In the below videos I'm only placing my finger on the other end of the RCA cable to provide some resistance and watch the meters. No speaker cables are connected. Rear switches are in 2.5V, Stereo and Normal for Power Guard. Fuse is intact. Why is it upside down? I'm listening for the relays to switch on and keep an eye on things.

Working just fine:


No Signal:



Here's the truly bizarre thing: If I leave the 2205 upside down, it works 100% of the time. Right side up = maybe 10%. It's like she doesn't like to be moved. o_O In the second video, I had just moved it and that is why it wasn't working.

Any ideas or recommendations would be appreciated. I have a diverse vinyl collection that's ready for our listening pleasure!



Photos of the unit:

MC2205 Front

MC2205 Front


MC2205 Rear

MC2205 Rear


MC2205 Top

MC2205 Top

 
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Many possibilities.

Simplest things first: Switch the left and right RCA connections at the amp, ensure it's not your patch-cord.

Next, exercise the mono and sensitivity switches on the back of the amp and try again, could simply be dirty. Try pressing in on the switches lightly to see if that changes anything.
 
SaturationPt said:
Many possibilities.

Simplest things first: Switch the left and right RCA connections at the amp, ensure it's not your patch-cord.

Next, exercise the mono and sensitivity switches on the back of the amp and try again, could simply be dirty. Try pressing in on the switches lightly to see if that changes anything.
Click to expand...

Thank you. I have indeed done both. Tried several different RCA cables and have worked the switches. No luck. The upside down always working is what is really strange.
 
I had the exact symptom with an MC75, turned out that the thermistor on the power cord/input was delaminated from the connection, upside-down was enough movement from the weight of the thermistor to make contact and it worked.
 
Amps of this era (2125, 2205, etc) are notorious for having cold solder joints on the Power Output card connections. The amps are pretty simple in design and can be easily opened up to remove the card. You can then solder re-flow the pins on the cards. It’s also an opportunity to swap the cards to see if the issue follows or stays on the “problem” channel.

The speaker relay is also getting leggy if it’s never been replaced. One of those “while you are in there” kind of scenarios.
 
If the meter isn't moving (as it appears in the second video), it's not the speaker switch nor the thermistor that I mentioned above.
 
Mouser Potter & Brumfield KUP14D15-48. $22

Do a search here regarding installation. There are an extra, unused row of pins and the clear plastic cover is different.
 
jlovda said:
Mouser Potter & Brumfield KUP14D15-48. $22

Do a search here regarding installation. There are an extra, unused row of pins and the clear plastic cover is different.
Click to expand...

Appreciate it. I think I saw a YT video about those pins while I was researching this. Will find that thread..
 
Caesar Swift said:
Went back through everything and found the Left Channel PCB had an issue in this connector. She's right side up and humming along! Thanks for all the suggestions.


MC2205 Left Channel PCB

MC2205 Left Channel PCB

Click to expand...
Is that a new photo? It looks like you still haven't replaced the two German burgundy 10uf bipolar caps on the board. These are well known to fail due to old age.
 
jlovda said:
Is that a new photo? It looks like you still haven't replaced the two German burgundy 10uf bipolar caps on the board. These are well known to fail due to old age.
Click to expand...

Yup, recent pic of when I was troubleshooting the other day.

Thanks for that recommendation. I'm going to do a full refresh in the coming months - just glad to be able to listen to some records currently.
 
Caesar Swift said:
Yup, recent pic of when I was troubleshooting the other day.

Thanks for that recommendation. I'm going to do a full refresh in the coming months - just glad to be able to listen to some records currently.
Click to expand...
I thought maybe you still had the amplifier open. Just about everyone uses green Nichicon Muse 10uf 50v caps for this application. I haven't checked but I am hearing a lot of the Nichicon caps are out of stock at Mouser and Digi-Key. Good luck.
 
jlovda said:
a lot of the Nichicon caps are out of stock at Mouser and Digi-Key. Good luck.
Click to expand...

Can confirm. I re-capped a 2205 and had to “settle” with a lower audio grade Nichicon instead of the green Muse for the 10uF BP’s. Still sounds great. I wouldn’t buy them from anywhere except Digikey or Mouser, or a legit boutique electronic supply because of fakes. The Fine Gold’s were out of stock in certain flavors as well, with long resupply dates.
 
krisOK said:
Can confirm. I re-capped a 2205 and had to “settle” with a lower audio grade Nichicon instead of the green Muse for the 10uF BP’s. Still sounds great. I wouldn’t buy them from anywhere except Digikey or Mouser, or a legit boutique electronic supply because of fakes. The Fine Gold’s were out of stock in certain flavors as well, with long resupply dates.
Click to expand...
Good looking out. I'll keep an eye out for that stock.
 
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