Langevin AM16 Racking help

[dustbro]

Hello All!
I'm having a heck of a time racking up some Langevin AM16 preamps, and I can't figure out what I'm doing wrong.  I have 4 modules here all doing the same thing. I connect power and my rails drop from 24V to 3V.  I've tried 2 different PSU's, so I don't think that's the issue. From the schematic it looks like I connect +24V to pin M and ground to K.
HELP!!

 

[PRR]

How do you know they are healthy? Sure sounds like a box of "to be fixed" board that never got fixed.

Current is supposed to be 55mA in "low" (110mA in high). http://www.benmook.com/tech/documents/Schematics%202/Schematics%202/Langevin%20AM-16.pdf

 

[dustbro]

How do you know they are healthy?

Good question!  I don't. ... but I automatically ruled out unit failure since 4 were exhibiting the same behavior.  Welp ...  time to get schwifty!

 

[emrr]

PSU and module chassis has ground reference?

These ring heavily, and need at least a 1k output load resistance. 

 

[mjrippe]

It is possible that C1 is bad on all four modules...easy to check.

 

[emrr]

It is possible that C1 is bad on all four modules...easy to check.

Yes, those should go on principle. 

 

[Rob Flinn]

Are you connecting all 4 modules simultaneously ? If s,o you may have a fault with 1 module only.  If so try 1 module at a time with the psu's.    Another problem that connecting all 4 modules may have is if the PSU's don't have the AMps to supply 2 modules.

If you are connecting them indvidually for testing & all modules work then please ignore the above....