Re: KPA/KAT500 Mystery Fail - solved

[kd4iz]

Thanks to some (kind advice and well deserved goading) from Mike, K6MKF and Ken, WA2LBI – I worked out the issue – unfortunately the fix appears to be a visit to ICOM repair if access to components is as bad as I fear.

 

For the general edification of other ICOM 7XXX owners:

Two KEY control lines go from the ICOM 7100 and 7300 rigs to the KPA/KAT500 combo.

1. The ICOM Molex connector KEY line is part of the TUNE/operate trigger function to the KAT500 along with the START line.  
2. Pin #3 (HSEND) of the 13 pin DIN connector is the KEY function used by the KPA500 KEY line input. It is a bi-directional line.

 

Normally, HSEND appears to float at about 6 volts. If this line is pulled low by external equipment, the transceiver is keyed. When the transceiver is keyed, the line is pulled low, keying external equipment. Maximum line current 200ma. This is what the 7300 was doing… so all was OK there but... My 7100 showed an HSEND float voltage of 2.3V and did not drop to ground when the rig was keyed – apparently the keying circuit is smoked. Looks like there is a diode in between the circuitry and the connector (hope-hope). Not sure why this blew because these puppies have been in use with the KPA500 and relatively trouble free for a while from what I understand… probably operator error/shuffle static damage on my part. Glad it wasn’t a KAT/KPA500 issue.

 

Thanks for your patience,

 

KD4IZ

Jack Spitznagel

FM19oo

 

 

 

From: Ken Winterling <[hidden email]>
Sent: Sunday, March 10, 2019 11:33
To: [hidden email]
Cc: Elecraft Reflector <[hidden email]>
Subject: Re: [Elecraft] KPA/KAT500 Mystery Fail

 

Jack,

 

I assume the two cables you use are the RF coax cable and the PTT keying line, correct?  The keying line should connect from the rig, then to the KAT500, and finally the KPA500.  This allows the KAT500 to disable the keying for the KPA500 during tuning or high SWR conditions.

 

It is possible that with moving the cables between the two rigs the keying line cable has been damaged.  I have seen this before where a cable works fine in one jack but not in another.  It is a matter of the cable being in just the right position.  If you rotate it slightly it goes OC (Open Circuit).

 

To simplify troubleshooting I would eliminate the KAT500 and plug the keying line directly from the IC-7100 into the KPA500.  Put the amp on a dummy load.

 

You said the '7100 doesn't key the KPA500.  You can check the KPA500 display for an asterisk (*) on the left side indicating that the amp is receiving a keying signal (contact closure to ground) from the rig ('7100).  If you do not see that asterisk (*) then the amp is not  being keyed by the rig.  Try a different cable to the rig.  

 

If that doesn't work then try leaving the keying cable plugged into the amp and unplugging the cable from the rig.  Touch to ground the center conductor of the end of the cable you removed from the rig.  It should key the amp and show the asterisk (*) in the display.  If the amp keys with the cable grounded then it it time to look at the keying jack/circuit of the IC-7100.

 

Let us know what you find.

 

Ken

WA2LBI

 

 

 

 

On Sun, Mar 10, 2019 at 10:28 AM <[hidden email] <mailto:[hidden email]> > wrote:

All,

I have been using the KPA500/KAT500 combo with an IC-7300 and an IC-7100 for
around a year now. They are cabled and configured as per the Elecraft device
manuals. The cabling is identical for the two transmitters (actually, I use
the same 2 cables for both). All has been working properly with both radios
until very recently. The amp and the tuner continue to behave properly with
the 7300.

 

The KAT500 continues to work perfectly with the 7100, however the
KPA500 no longer band switches when I change bands on the 7100 and key up.
In addition, the amplifier will not key. The 7100 still can put out full
power with the KAT500 in line. I have not changed any setting in any of the
3 devices to my knowledge. It is like the KPA500 has become deaf to the
IC-7100.

After switching back and forth and looking at all device settings, I am
baffled at this point! Is there anything in the way of rig to amplifier line
signals that could inhibit band switching by the amplifier but not by the
antenna tuner?

Thanks for your thoughts.

KD4IZ

Jack Spitznagel

FM19oo

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