[ICOM] 756 ProII low power

[Simon Watt-Wyness]

Hi,
Sounds almost if it is something like a relay in the TX low pass filter
area. If you get full noise on the lower bands but only 50 or so on TX
with 16A drain tells me that final board still ok. Maybe check other
bands between 10MHz & 24MHz to see what behaviour is there. Form there
you maybe able to isolate a crook relay or path through the LPF out to
the antenna.

Oh and another thought... How are you measuring the power? External
Meter or the one in the radio? If internal, it's not switching between
antennas between 1 & 2 by any chance? The rig O/P power will be down due
to SWR protection if no antenna connected to one of the ports..

Just my 5c worth.

Cheers,
Simon ZL1SWW


-----Original Message-----
From: icom-bounces at mailman.qth.net [mailto:icom-bounces at mailman.qth.net]
On Behalf Of Paul Ferguson
Sent: Monday, 25 February 2008 12:29 p.m.
To: ICOM Reflector
Subject: Re: [ICOM] 756 ProII low power

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/


----
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/
===
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