Icom: IC706MKIIG problem starting AH04

[KA5Z]

Hello,
The radio has ceased triggering the AH-4 tuner. One time CPU reset on the radio cured the issue for a day, now no reset seems to help. Noted that the THSTART line from radio is at low logic level. a 2.2K resistor can pull the line up. Briefly shorting the THSTART line to gnd does not trigger the AH4 KEY line. Any thoughts on next steps to take? Thanks very much.

 

[AK9R]

I can only think of the basic stuff that you've probably already tried: verify the integrity of the power supply to the radio and make sure the tuner connector contacts are clean and not bent out of shape.

 

[KA5Z]

Thanks for reply. Yes, all the usual checks. There is a concern that the cable length may be excessive, however, the setup has performed well in the past. My next step will be to open the AH-4 and disconnect the START line to see if the AH-4 pulls the line up, or only the radio does the pull up. Assertion is pull to logic low. I'm hoping that the radio is not damaged, as there are no transient suppressors on the cable, which runs mostly on the ground before entering the house and thence to the radio.

 

[AK9R]

I've run AH-4 tuners from Icom base radios, not the 706, with as much as 100 feet of control cable. No problems.

 

[KA5Z]

Problem solved!

Further investigation at the AH-4 (mounted outside) revealed that the 13volt conductor in the cable was not providing 13 volts! Measured only 2 volts! Replaced the cable, about a 35 foot run, and the system now operates normally. The AH-4 provides the pullup for both signal lines, START and KEY. The IC-706MKIIG provides the pulldown for the START and senses the KEY line state.

Thanks to W9BU for reply to my first post on radioreference!

Richard KA5Z