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McIntosh C31V issue...

dschulma

dschulma

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Good evening everyone, new member here. I thought that maybe someone could help with an issue that a friend of mine is having with his McIntosh C31V. Below is an excerpt from an email I received from him.

"When I turn this one on, it seems to default to AUX1. The panel buttons will switch the inputs, only some of the time. The remote works better, but it always returns to AUX1. I don’t know if this is the way it is supposed to work, or if it has a problem."

Is there a way to reset the unit back to factory defaults, is it just a user setting, or does this sound like a more involved issue? Thanks in advance for any advice!

David
 
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Perhaps the AUX pushbutton is sticking or the switch itself. Look to see if the AUX pushbutton is detented slightly from the rest. This would indicate the pushbutton is sticking therefore selecting the AUX input. I have seen this once before.

The C31V has a backup power supply so it should retain the last input selected. I would have a tech take a look at it if it isn't a stuck pushbutton. There is no reset on this preamp.

David
 
If the back up power to retain memories is a battery, suspect it. They're getting old and erratic behavior with symptoms you're reporting would be typical of that sort of failure.

Cheers,

David
 
STUCK ON AUX2...
I have a related problem with a C31V.
When I select the Aux1 or Phono inputs with either the remote or the face plate switch,
Aux 1 or Phono will be lit for a few seconds and then Aux 2 illuminates.
The desired input will not remain on/selected.
I have cleaned all of the pin connections.
Please let me know what I should next pursue.
Thanks.
 
[QUOTE="jblmar, post: 9287405, member: 3187"
Do you have the owners yes
or service manual? No
Did you contact McIntosh? No answer from yesterday
[/QUOTE]
 
RDecartridge said:
[QUOTE="jblmar, post: 9287405, member: 3187"
Do you have the owners yes
or service manual? No
Did you contact McIntosh? No answer from yesterday
Click to expand...
[/QUOTE]
Is there a 'Troubleshooting Chart' in the owners manual?
If yes, can you post it here?
If there is a back-up battery or capacitor, can you check its condition?
 
There are two different versions. Early units used Toshiba multi switch volume control, later units used a motor driven Alps pot.

Are you comfortable turning this unit into a brick? Many, many static sensitive JFET and CMOS chips are uused throughout the logic circuits in this unit.

Really should go to your local tech with a check.
 
c_dk said:
There are two different versions. Early units used Toshiba multi switch volume control, later units used a motor driven Alps pot.

Are you comfortable turning this unit into a brick? Many, many static sensitive JFET and CMOS chips are uused throughout the logic circuits in this unit.

Really should go to your local tech with a check.
Click to expand...
That's why I asked for the Troubleshooting Chart, To get familiar with the design of the circuits as well as the necessary test gear.
 
There is no trouble shooting chart.
Attached are pics of the 3 boards. Please let me know if you see a battery or battery capacitor.
Thanks. 20151223_120655.jpg 20151223_120705.jpg 20151223_120722.jpg
 
I believe the original ER and FR series schematics had a flow chart of sorts, the combo schematic does not.

I have never seen a battery in any of these preamps, the tuners did but not preamps.
 
What was the conclusion of this problem?
My C31V is having same problem.
Keeps returning to AUX2 after a few minutes.
Then locks switches altogether even after power cycle.

My 2505 is lonely without its preamp!
 
This is an old post but I'm old too so I wish to share what the main issue is with random input commands on the C31v. I have seen this before a few years ago. It happens when the glass is improperly cleaned and the liquid seeps down onto the top of the selector circuit board. There is a metal strip along there that is glued to the top of the board by a strip of rubber. The corrosion continues over the years until the traces under the glued strip and the metal bar start to corrode. The rubber and glue start to conduct (leak current) which in turn causes the micro to receive random commands. You have to remove the board from the back of the front panel, pry the metal strip off and clean the rubber and glue off the metal and pc board. If the traces are still intact, you're OK. I usually cut that top trace and rewire it with #30 wire point to point so it won't be a problem again. I use fiberglass tape to provide insulation for the metal bar and pc board when reinstalling. I hope this will help some techs as I haven't seen anybody else find this issue and correct it. Never spray glass cleaner directly on these McIntosh pieces. Spray the cleaning cloth then wipe.
 
Garysaudio said:
This is an old post but I'm old too so I wish to share what the main issue is with random input commands on the C31v. I have seen this before a few years ago. It happens when the glass is improperly cleaned and the liquid seeps down onto the top of the selector circuit board. There is a metal strip along there that is glued to the top of the board by a strip of rubber. The corrosion continues over the years until the traces under the glued strip and the metal bar start to corrode. The rubber and glue start to conduct (leak current) which in turn causes the micro to receive random commands. You have to remove the board from the back of the front panel, pry the metal strip off and clean the rubber and glue off the metal and pc board. If the traces are still intact, you're OK. I usually cut that top trace and rewire it with #30 wire point to point so it won't be a problem again. I use fiberglass tape to provide insulation for the metal bar and pc board when reinstalling. I hope this will help some techs as I haven't seen anybody else find this issue and correct it. Never spray glass cleaner directly on these McIntosh pieces. Spray the cleaning cloth then wipe.
Click to expand...
How do you get to that board? I’m having a similiar problem with power button. I’ve taking it all apart but can figure out how to access the board behind the buttons.
 
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