[Elecraft] KPA500 not responding to K3

[Ben Collins-Sussman]

OK, new test results, followed by an inexplicable resolution to the problem!

I'm comparing the two elecraft-specific DB15 cables here, with the
suspicion that one of them is broken or defective.

1.  *Physical observation*

The K3/KPA cable has all pins present.
The KPA/KAT cable has pins 1, 6, 7 missing.  But it looks deliberate, and
those pins are not used anyway (according to documentation.)
I do not see any bent pins on either cable.


2. *Communication directly between radio and amp*

When I connect the radio and amp directly together using the K3/KPA cable,
three things work:

   - the amp follows the radio's band-switching.
   - placing the amp in OPER causes the radio to print 'KPA500' on the
   screen.
   - keying and amplification works properly.

When I connect the radio and amp directly together using the (slightly
suspect) KPA/KAT cable:

   - the amp follows the radio's band-switching.
   - keying and amplification works properly.

The only unusual thing here is that switching to OPER causes no message on
the K3 screen.


3. *Communication with tuner as 'middleman'*

When I connect the K3/KPA cable from radio to tuner, and connect the
KPA/KAT cable from tuner to amp, things don't work.  The radio and amp do
not communicate at all.

When I *reverse* the two cables above, *everything works perfectly.*


4. *Conclusions*

   - The cables are supposed to be wired identically, and yet they behave
   differently.
   - My problem is now solved, and I don't know why.  :-)