{Collins} Directional Coupler Problem

I picked up a nice looking 312B-4, was touted as working ... but the Power
Measurements are wacky.

Now, I have an HP Power Meter that just came back from the Cal Lab so I
am confident my power readings are OK.

Now, I put 110 watts (@ 21 MHz) through the coupler and get the following

Forward: 200 Watts   reads around 80 Watts
              2,000 Watts  reads around 60 Watts

I reverse the coax cables to read the Reverse Scale.

Reverse: 200 Watts  reads around 40 Watts
             2,000 Watts  no reading, nothing

I checked the resistors in the coupler, reading from the terminal strip (first I disconnected the leads) to the junction post in the coupler. I used a cal'ed
Keithley 196.

All readings were within a few %.

Any ideas what can be wrong ??

Thanks, Dick, W1KSZ

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