da_ardvark

1604 mackie mixer question
« on: June 14, 2007, 02:38:11 PM »
I have a little problem. Not sure if this will help narrow it down.

On Channel 1 the Mute led is shares function with overload detection. If i press the mute button, the led lights brightly. If I remove mute (this just started happening) the led is still lit, just not a bright.

The section of the schemo is



The way I see it the red LED D104 has current flowing even without the mute switch. I'm suspecting the opamp U102A is not functioning properly.
The entire schemo is from gyrafs DIY page at the bottom. This is page 4 of the entire pdf.

Any comments of my sluthing????


kazper

1604 mackie mixer question
« Reply #1 on: June 17, 2007, 10:58:59 AM »
Could the mechanical switch for the mute button possibly be not working?
Intentionally left blank

SSLtech

1604 mackie mixer question
« Reply #2 on: June 17, 2007, 11:13:49 AM »
DC offset at the output of U102. Causes the LED to light slightly.

Fairly common on those things.

Keith
"A waist is a terrible thing to mind"
Quote from: PRR
Ah, but that was 1999; we don't party like that any more.

da_ardvark

1604 mackie mixer question
« Reply #3 on: June 18, 2007, 11:05:35 AM »
Thanks for the feedback. It's kind of weird because this problem doesn't seem to cause any noise, and appears intermittant. Meaning at times the light will dim, and eventually go out at times.

I dont' think its the mute switch bucause it still functions properly, but I guess I can't rule it out entirely.

I think I'm going to leave well enough alone for the moment. I'll keep my eye on the problem and see if it worsens.

SSL, can you suggest substitues for U102 that would be better suited?

Thanks again

CJ

1604 mackie mixer question
« Reply #4 on: June 18, 2007, 06:48:34 PM »
Neve 1073 might work better.  :twisted:
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

dale116dot7

1604 mackie mixer question
« Reply #5 on: June 18, 2007, 07:30:26 PM »
ESD damage through the LED or mute switch is possible. Also, check out any electrolytic caps just upstream of U102 - look for DC offsets in the various stages before this one to see if the problem comes from there. Also, an open-circuit 'pull-to-ground' resistor can create these problems as well.


-Dale

BYacey

    Where dogs wear thermal underwear, Alberta, Canada
  • Posts: 769
1604 mackie mixer question
« Reply #6 on: June 21, 2007, 02:55:27 AM »
Check your power supply regulators for correct tracking, could be one rail is out a little compared to the opposite one.
Bill Yacey
"Adjust R116 for least smoke"


 

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