[ICOM] PRO III bias setting

hamop k5yy at cox.net
Mon Aug 13 18:33:07 EDT 2012


Larry.
  IF you get a chance, is it possible to "copy" and then "paste" that page 
4-4 that has your bias setting explanations? The page 4-4 in the older 
service manual that NS0I linked us to has it all in one page, including the 
current measuring points. But, each PRO III version is different, the 
earlier ones were bipolar whereas my unit is a later one with MOS FETs. Your 
explanation is for MY vintage it appears. That one complete 4-4 page would 
be nice to have if easy to copy for me. Again, I appreciate your comments on 
the quiescent bias condition of the 4 devices with the 4 specific pot 
adjustments. I just wonder WHERE do they suggest you measure current to get 
that magic 1 amp static current? Are there spots to unsolder to put in a 
small ammeter to measure or are there some easy access to the current paths? 
hi
  THANKS so much again!
San K5YY

-----Original Message----- 
From: Larry Benko
Sent: Sunday, August 12, 2012 12:05 PM
To: icom at mailman.qth.net
Subject: Re: [ICOM] PRO III bias setting


I have the service manual in pdf format and it is 24MB. Chapter 4
describes all the adjustments.  Page 4-4 says measure idle current and
adjust R14 driver) for an increase of 1A, then adjust R16 (driver) for
an increase of 1A, then adjust R65 (final) for an increase of 1A, and
finally adjust R67 (final) for an increase of 1A.  Procedure was started
with all pot. fully CCW.

This would imply that all 4 devices in the driver and final section have
a quiescent bias of 1A.

Larry, W0QE





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