Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: icom 756 pro 3 low power  (Read 3197 times)
N4ZY
Member

Posts: 81




Ignore
« on: April 12, 2013, 12:02:08 PM »

my icom 756 pro 3 has low power 68 watts.i have been searching for a internal adjustment to try to improve. . on schematic it shows r 507 hp output power adjustment.i can find on the circut board where r507 should be. but there is no var resitor at that point.just the mounting holes ?? any help!!!!
                       Jim n4zy
Logged
W5DXP
Member

Posts: 3553


WWW

Ignore
« Reply #1 on: April 12, 2013, 12:16:03 PM »

my icom 756 pro 3 has low power 68 watts.

Is that into a 50 ohm dummy load or what?
Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
N4ZY
Member

Posts: 81




Ignore
« Reply #2 on: April 12, 2013, 01:51:07 PM »

that is in to dummy load and 3 different antennas
Logged
W4VR
Member

Posts: 1191


WWW

Ignore
« Reply #3 on: April 12, 2013, 01:55:05 PM »

has the power output always been that low or is this something new?
Logged
G4IJE
Member

Posts: 243




Ignore
« Reply #4 on: April 12, 2013, 02:22:22 PM »

Is it the same on all bands? It might a filter issue. And you've definitely measured something nearer 100 watts in the past, using the same meter, cables, dummy load etc, that you are using now?
Logged
K5WLR
Member

Posts: 91




Ignore
« Reply #5 on: April 12, 2013, 02:48:25 PM »

You also might want to check the fuses and the power plug on the back of the radio. The fuse holder Icom used on these radios have a tendency to get loose with age and they develop some resistance. I had fuse holders that turned dark brown from the heat this generated. The female connections on the power plug can splay out from repeated connections and disconnections, causing a similar drop in voltage to the radio, which in turn will cause low output.

Hope this helps!

73!  Cool

Will Rogers
K5WLR
Logged
WA3SKN
Member

Posts: 5457




Ignore
« Reply #6 on: April 12, 2013, 03:36:38 PM »

Does the audio sound "clean" or distorted?

-Mike.
Logged
W5DXP
Member

Posts: 3553


WWW

Ignore
« Reply #7 on: April 13, 2013, 07:18:21 AM »

Please don't get upset at me for asking stupid questions: Is the power output potentiometer fully clockwise? Is the built-in antenna tuner turned off? Are you reading the power output from the IC-756 panel meter or using some other power measurement device? Are you using CW/RTTY mode, i.e. not SSB or AM?
Logged

73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
N4ZY
Member

Posts: 81




Ignore
« Reply #8 on: April 13, 2013, 07:30:55 AM »

i believe the audio could be better
Logged
N4ZY
Member

Posts: 81




Ignore
« Reply #9 on: April 13, 2013, 07:57:58 AM »

power out put read from rig,bird 43 100 watt slugalso 1000 watt slug,drake W-4. readings within 5 watts of each other
Logged
N7SMI
Member

Posts: 326




Ignore
« Reply #10 on: April 13, 2013, 07:59:51 AM »

I had a similar issue with my Pro 2. I sent it off to Icom and they returned it with a note indicating they made several adjustments to the power, ALC, and other pots. It works like a champ now.
Logged
N4ZY
Member

Posts: 81




Ignore
« Reply #11 on: April 13, 2013, 08:05:07 AM »

w4vr.. it hasbeen since  i had the rig repaired for no rig to computer talk. no rtty/psk.  i checked that part of rig when i got it back from shop. BUT did not pay attention of power out put
Logged
K8AC
Member

Posts: 1465




Ignore
« Reply #12 on: April 13, 2013, 10:34:32 AM »

Depending on the vintage of the Pro III, there were two different PA boards used.  So, if you have the diagram for the wrong board, that's why you can't find the pot.  I ran into the same problem a few years back.  In what mode do you see the reduced power output?  If you haven't done this already, measure the output in CW mode with the key closed.  I had one Pro III that showed lower output in SSB mode (80 watts max) when fresh from the factory, but full power in CW and RTTY.  I sent it to Icom on the west coast and they returned it a few weeks later saying they could find no problem.  I put it back on the bench in the same test setup and mysteriously the output was now 100 watts as it should have been in the first place.  My testing was done with an accurately calibrated audio signal generator and precision wattmeter.  I suspect that there was something misadjusted from the factory and the service guys just ran through the PA adjustment and all was well.  I'm pretty sure that the Pro III service manual was eventually updated with the correct diagrams for the MOSFET PA boards that came later.

Logged
K5WLR
Member

Posts: 91




Ignore
« Reply #13 on: April 18, 2013, 10:04:55 AM »

Any updates? Just curious.... Cool
Logged
KE3WD
Member

Posts: 5694




Ignore
« Reply #14 on: April 18, 2013, 01:07:00 PM »

The OP never really stated what mode of transmission was being used for this "test" - if the mode was SSB, and not CW or FM, then the 60W figure coupled with a non peak-reading wattmeter would actually be about right. 

The past few years there seems to be a plethora of operators who do not seem to understand the workings of SSB, that it contains little to no Carrier and that reading the output wattage requires modulating the mic and use of a peak-reading wattmeter to see the full 100W. 


73
Logged
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!