[ICOM] 756 ProII low power

[Paul Ferguson]

Thanks for the suggestions. 

I am using the supplied Icom cable (about 9 ft long) and my power supply is an 
Astron 35M. It has been working fine for several years.

I removed the 756ProII top and made some measurements. Here all the voltage 
measurements from the power supply to inside the transceiver made transmitting 
on 24 mHz, where power output is only about 50 watts. The two voltage readings 
for each point are at idle current then at key down:

At the power supply output lugs:  13.74, 13.72

At input (power supply side) of the fuses:  13.66, 13.35

At output of the fuses:  13.64, 13.28

At the circuit board inside the transceiver:  13.62, 13.14 

Power Supply current goes from about 3.5A at idle to 16A at transmit on 24mHz.
 

When I transmit on 10 mHz or lower, power output is 100+ watts. Power Supply 
current goes from about 3.5A at idle to 21A at transmit. Measuring inside the 
transceiver the voltage is 13.62 at idle, and 12.97 at transmit.

I am getting a voltage drop between the power supply and inside the transceiver 
of 0.6 to 0.75 volts. Would this amount of voltage drop cause the transceiver 
to have problems generating full power out above 10 mHz?

I inspected the cable, pins, fuses and did not see a problem. I also tried 
wiggling all connections while making measurements, but could not see changes.

73,
Paul
K5ESW

> Paul: It does little if any good to measure your power supply voltage at the PS
> end of the cable. You also do not mention if you are using the oridinal Icom
> power cable which can sometimes drop a lot of voltage not only in the cable but
> in the series fuses as well. Rhis is why the Icom PS-125 uses very short power
> leads with no series fuses in the power leads. I know it is a pain to slip back
> the boot covering the end power connector at the rig, and measure the voltage
> there or remove the top cover and measure the voltage at the back inside of the
> radio.To not do this first is like replacing Ohms law with Voodoo.73, Larry
> K4LXV. ---- Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net Icom
> Users Net: Sundays, 1700Z, 14.316 MHz Icom FAQ: http://www.qsl.net/icom/