[Elecraft] Grounding gear

[Ron]

Hi gang,
             I know grounding has been flogged on this Reflector before but 
I have a question to ask the collective about a problem I have struck.
A while ago, I managed to convince an interested party to buy a second hand 
K2/100 complete with KAT100, that came on the market at a good price. I knew 
the set as I had built it myself and had every confidence in it, however not 
long after the new owner took delivery, I received a report that it had gone 
"bang" and smoke had come out of it, and it wouldn't work anymore on the 
KPA100. The amplifier was sent up to me and it was found that 2 of the  T/R 
1N4700 diodes  were short-cct...the smoke had been provided by R40 burning 
out.
The amplifier had been previously been bought up to the latest specs, but 
C64 hadn't been changed to the larger value now specified, so I suspected 
that must have been the culprit. I replaced the diodes, resistor, Cap,and 
ZVN4424's (just in case) and tested the amp as OK on anything I had here.
The amp was returned and has run for a month or so, until I received notice 
that it was playing up again.
The problem arose on the same antenna as before, which is a 40/20m vertical, 
that apparently the KAT100 has always had a bit of trouble finding a match 
on, and once again, when TUNE had been initiated, all the LED's on the ATU 
lit up and the set locked up.....it was apparently tried a couple of times 
before the fuse in the 13.8v lead blew. It sounds to me like RF feedback 
upsetting the rig and causing the amp to oscillate?
Now.....in this particular shack, the chap does not ground his gear, but 
rather uses counterpoises on his long wire ( connected to where I am not 
sure) and radials on the vertical ( which I presume are above ground as it 
is a roof mounted vert), but no ground wire connected to the K2/100 or 
KAT100.
Am I right in assuming a "ground" connection on the K2 "may" help? ( 
Elecraft provide the terminals?)....I would have imagined the set shouldn't 
"take off" under any reasonable circumstances, but when RF feedback (as I 
suspect) comes into the equation anything can happen.
Any ideas??
Regards.....Ron ZL1TW