API 312 oddity

[pucho812]

Got a Brent averel 312 that is behind oddly. If I hook it up to my test jig which is a bench supply and an edge connector I have it working, with the ap I can run a -20dBU 1k sine wave into it and get +14dbu on the output with gain pot at lowest setting.  The wave looks clean and the pot works as it should. I can get upwards of 30dBu at the output.

But the moment it goes into a chassis, it does not work at all. I get a lot of noise, the opamp gets warm to touch and no gain control.  This is with 2 different API racks.
I suspect a faulty opamp.  But hard to find as it works in the test jig. According to the bench supply current draw is what I would expect to see.

 

[pucho812]

nevermind, found it. It was opamp related. faulty solder joint...  8)

onto the next one.

 

[ruffrecords]

Interesting. So, do you think it was basically mechanically related? That is, fitting it into a rack flexed the PCB is such a way that the dodgy joint went open or hi-z?

Cheers

Ian

 

[pucho812]

Interesting. So, do you think it was basically mechanically related? That is, fitting it into a rack flexed the PCB is such a way that the dodgy joint went open or hi-z?

Cheers

Ian

good question. When I removed it from the rack(put in after bench testing first time.  it exhibited the problem that was in the rack. pushing on the circuit board and joint caused it to go away. perhaps years of use has had the board flexing enough to cause intermittent issue.  I reflowed the joint and was good. Pushing on the same spot and no intermittent problems like the second round of testing.