AML 52F50 issues

[MHProd]

Hi everyone,

I just finished building a pair of 52F50 and attempted to calibrate them but quickly ran into an issue...

One calibrated fine.

I started the other one, adjusted the bias to 130mA and then as I was trimming the output, my meter went close to 0 suddenly.

Checked the probes, checked the input and then I started to smell something "hot", I checked the the bias resistor and it was drawing 345mV... Tried to turn the bias down (or up) and no effect on the reading.

I might have fried something but since there are no voltage test points in the manual, I'm not sure where to start...

Thank you for your suggestions!

 

[andYz00m]

How are you measuring the bias voltage? Are you using the R156 method? Or do you have a power supply that can read current draw?

Myself and many other users have found the R156 method to be unreliable.
Also see this thread.

 

[MHProd]

Yes, I'm measuring it across R156. It worked fine initially but like I said, I lost my output signal and it started to smell like hot plastic. The bias trimmer doesn't change anything and it's now drawing almost three times the specs... I was getting a very stable reading over the resistor on both units. Now this one just shows 345mA...

Thanks, I had read this thread before posting.