Quad Eight MM71 trouble

[ubxf]

Hello,
i have a few Quad eight MM71 that i just took out of storage they all work except for a couple. I changed the electrolytics and followed the signal through from the input to the third opamp . I get signal on pin 9 that goes up and down with the fader but nothing on pin 7 and nothing on pin 2. I swapped the AM4 opamp  with one a took out from a CN28 i had but still no luck.
The voltages on pin 5 and 12 are good. Besides hiring someone who knows what they are doing : ) could you suggest something else i should try. Many thanks

 

[mjrippe]

Are both of the non-working units doing the same thing?  Are you sure the AM4 you are subbing in is good?  Did you double check all the new caps are right way round?  Not sure what else to look at at this point.

 

[ubxf]

Yes both are doing the exact same thing, all the caps are the right way but the AM4 is a pull from a module that is of unknown origin. I'm very hesitant to desolder an AM4 from one of the working ones. Is there a way to test the AM4 ? or can i sub something else for it just to see if it works

 

[mjrippe]

Unless you want to take the time and materials to build a test jig, you would have to put the "spare" AM4 into a known working module to test it, at which point you would have a known good AM4 already pulled...

 

[ubxf]

I would build a test jig but what part of the circuit should i include

 

[mjrippe]

Honestly, I don't know.  I am not intimately familiar with the AM4.  My point was that it is easier to pull a known GOOD amp.

 

[ubxf]

Ok Thanks i will try to build the test set up based on the components i see on the schematic and see if it works

 

[orphanaudio]

Here is our current AM-4 series pinout sheet. We have opamps in stock if you need them as well as schematic copies for all versions of QEE gear. As I rarely have time to visit the forums, please contact us directly through the website for any parts, document or technical support needs.


Thank you,

Ken Hirsch / Director of Engineering
Orphan Audio www.orphanaudio.com
Quad-Eight Electronics www.quadeightelectronics.com
Electrodyne Audio www.electrodyneaudio.com (a division of Orphan Audio)

"Education is the cure for everything"