[AMPS] IC-756PRO/HF-2500 Problem

[Tom Rauch]

> With HF-2500 in Operate position, and RF Power turned to zero on 756PRO,
> when I key 756PRO in SSB, receiver sensitivity drops to almost nothing
> (most of the time). Only consistent way to bring is back is to turn amp to
> Standby, then switch to CW mode and key 756PRO with CW key (with or
> without RF Power). Sometimes whole system works okay, but mostly I lose
> receiver sensitivity. I have to go through the above procedure to be able
> to hear receive signals. Sometimes just keying the mic, with the amp in
> Operate position works, but mostly that doesn't clear the problem. System
> is the 756PRO, HF-2500 and Vectronics HFT1500 tuner into 80 mtr dipole.
> SWR is 1:1 (no reflected power). New ground system. New 8 ft. ground rod,
> 6 feet away.. No RF floating around. Some kind of relay problem in the
> 756PRO. Relay to ground output from HF-2500 goes to relay to ground
> connection on 756PRO. Strange that only going to CW position and hitting
> the key once is the only thing that consistently clears the problem.

Your symptoms are common for a bad connection in a T/R relay, 
roller inductor, connector, or almost anything else.

Does it do this with the Vectronics tuner on bypass? (By the way, 
the Vectronics tuner is MUCH too small for the HF2500.)

A clue might be clicking the mic with the amp in the operate 
position fixes the problem. Assuming the mic gain is down at zero, 
and the rig is not putting out  transients when you click the mic, 
that would indicate a relay problem in the amplifier.

What happens if you unplug the relay line from the amplifier? Can 
you "scratch" the relay line on ground with the amp on operate and 
restore the receive signal? If you can, it's almost certainly in the 
amp.

I doubt the problem is in the rig. You might bypass certain pieces 
of external equipment to see if you can find the problem. It could 
even be in a coax connector.
 
73, Tom W8JI
w8ji@contesting.com

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