[Elecraft] KPA500 Question

[ws6x.ars at gmail.com]

"When I engage OPER the input signal is attenuated by ~20 dB."

Thanks to all for the prompt and informative replies. Apparently the culprit
has been found. Several reported the exact same issue, one as recently as
one week ago. According to one reply, an Elecraft Tech told him, "This is a
known failure mode." (Not very encouraging!)
Here is a copy of an Elecraft repair report:

Reported problem(s):
Receive signal is attenuated when in operate. Receive signal is normal when
in standby.

Problem(s) found:
Confirmed problem. Found that D8, D9 and R7 in the T/R circuit had failed.

Repair(s) performed:
Replaced D8, D9, and R7 on the LPF board.

Looks like my KPA500 is in for some "belly up" treatment!
One thing has me a bit puzzled though. If this is a known weakness, why
hasn't Elecraft designed a "beefed up" mod? My amp had 5 updates / mods done
while it was at the factory. This "known failure" was not one of them. 
Thanks again, for all the help!
Jim - WS6X