SSM2167: Chinese module AGC problem

I cannot make PCBs for MSOP devices so I bought some modules through Ali Baba. Several suppliers offer the same module. It works correctly with 1:1 compression but not with any other resistor value from Pin 8 to Vcc+ (3 V). It stays in 1:1 mode. For 10:1, I am using 180k. In view of the wide availability of these modules, I wonder if anyone else has made them work or found the problem and cured it. What can I do in the way of probing the module to try to find what is wrong.

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    •  Analog Employees 
    on Jan 20, 2020 5:15 PM

    Hello LMW,

    From looking at the picture, R2 is the compression ratio resistor. I would remove it and use an ohm meter to see what the resistance is from pin 8 to +Vcc. It should be close to open. 

    Then make sure the far side of R2 is indeed connected to +Vcc. Other than that there should not be much more to it than that? 

    Make sure you are putting in a signal that is loud enough to go over the threshold. If you are never reaching the knee point of the compression curve then it would be 1:1. 

    So those are my first thoughts. 

    Dave T