Newsgroups: rec.radio.amateur.misc
Path: elroy.jpl.nasa.gov!decwrl!csus.edu!netcom.com!wa2ise
From: wa2ise@netcom.com (Robert Casey)
Subject: DR1200 InterMOD reduction mod file
Message-ID: 
Keywords: intermod
Organization: NETCOM On-line Communication Services (408 241-9760 guest)
Date: Fri, 30 Apr 1993 02:03:57 GMT
Lines: 40


copied from packet:
  Msg# TSF   Size  Date  Time  Arrived #Rd  Seq #      Msg ID      Route
   612 BF    2607 21-Apr 1643z 24-Apr    0 (002799 - 28806_W0LJF ) []
  K0ZL   ==>  MODS@USBBS
  "DR-1200 INTERMOD REDUCED"

                    ALINCO DR-1200 INTERMOD REDUCTION

CAUTION: THE FOLLOWING PROCEDURE INVOLVES DESOLDERING SMD (SURFACE MOUNT
         DEVICES).  IF YOU ARE NOT QUALIFIED TO WORK ON SMD DEVICES OR
         DO NOT HAVE THE PROPER EQUIPMENT, DO NOT ATTEMPT THIS MOD!  SEEK
         PROFESSIONAL TECHNICAL ASSISTANCE.  THE ORIGINATOR OF THIS
         MODIFICATION IS NOT RESPONSIBLE FOR ANY LOSS INVOLVING THE 
         PERFORMANCE OF THIS MODIFICATION.
         
CAUTION: THIS RADIO EMPLOYS STATIC SENSITIVE DEVICES.  SUITABLE MEANS SHOULD
         BE EMPLOYED TO ASSURE A STATIC-FREE ENVIRONMENT PRIOR TO BEGINNING
         WORK ON THIS RADIO.

1.  REMOVE POWER AND ANTENNA FROM RIG
2.  REMOVE BOTTOM COVER
3.  LOCATE C-19, LEFT SIDE FRONT OF BOARD (CLEARLY LABELED, NEAR Q3).
4.  REMOVE C-19: SUCK UP THE SOLDER AND CAREFULLY PRY AWAY
                 FROM BOARD WHILE STILL WARM.
5.  SAVE THE CAPACITOR IN CASE YOU GOT THE WRONG PART!
6.  REASSEMBLE THE RADIO, NO RETUNING NECESSARY.

This capacitor connects D1 (back to back diodes) to the first IF line.
D1 is supposed to be a "limiter".  Unknown why Alinco chose to put in 
such a limiter, as the integrated IF chip IC-1, an MC3357, has a built-
in limiter.  Also, the Kenwood TM-231 which uses nearly the same layout and
circuit, doesn't have such a ciruit.

While the intermod hasn't gone away entirely (I'm not done with it yet!), it
has diminished enough to make the rig usable on packet AND voice now.

73 de Bill, K0ZL@W0LJF.#NECO.CO.NOAM
===============================================================================
Note: I haven't tried or verified this. proceed at your own risk.  WA2ISE