From: parnass@cbnewse.cb.att.com (Bob Parnass, AJ9S)
Subject: Re: R7000 relay replacement with solid state switch?
Organization: AT&T Bell Laboratories, Naperville, IL
Date: Sun, 6 Sep 1992 23:07:04 GMT
Summary: speed up the R7000 scan rate

In article <t0nn0p-.crisp@netcom.com>, crisp@netcom.com (Richard Crisp)
quotes another person on the Icom R7000 :

> "Some users have reported that a further improvement in scanning speed can
> be obtained by connecting a 470 ohm resistor across R18 on the R7000
> logic board."  ...
> Perhaps if anyone does try it before I get
> around to doing it, they will be willing to share their experiences
> with the net? I will when I do it.
> 
> -- 
> Richard Crisp                 Cupertino, Ca.                crisp@netcom.com
> (415) 903-3832 wk  "Time for a clean sweep of Congress"
                                                   ^
                                                   |
Don't forget the executive branch! ----------------+   :-)

Now, addressing the scan speedup --  It's true, and here's a reprint
of the article I  published in Monitoring Times a few years back:


             MODIFY YOUR ICOM R7000 TO SCAN AND SEARCH FASTER

                            Bob Parnass, AJ9S

       This article describes how to increase the scan  and  search
       speeds  of  the  ICOM  R7000  receiver  by up to 60% without
       noticeable performance degradation.

                                Background

       The front panel SCAN SPEED control  on  the  R7000  receiver
       allows  the user to adjust the speed of scanning and search-
       ing operations, as well as the rate at  which  the  priority
       channel  is  sampled.  Rotating the control counterclockwise
       decreases the speed, and rotating it clockwise increases the
       speed.

       When the SCAN SPEED  control  on  my  R7000  (serial  number
       001400)  was  turned fully clockwise, the radio would scan a
       maximum of  about  8  channels/second,  or  search  about  8
       increments/second.   As the following table shows, the stock
       R7000 can scan about as fast as  a  Radio  Shack  PRO-30  or
       PRO-2003.

            TABLE 1.  Maximum Scan Rates of Selected Receivers

          _____________________________________________________
         |             Scanner               Maximum Scan Rate|
         |                                |  (channels/second)|
         |________________________________|___________________|
         | Kenwood TR-2600                |         1.2       |
         | Radio Shack PRO-30             |         8         |
         | Radio Shack PRO-2003           |         8         |
         | ICOM R7000 (stock)             |         8         |
         | ICOM R7000 (after modification)|        13         |
         | Regency M400                   |        13         |
         | Bearcat 20/20                  |        15         |
         | Bearcat 300                    |        15         |
         |________________________________|___________________|



                           R7000 Scan Circuits

       The scan rate of the R7000 is determined, in part, by a sim-
       ple  clock outside the microprocessor.  The front panel SCAN
       SPEED rheostat and resistor R18 (and other components in the
       LOGIC UNIT) control the speed of this clock.  The clock out-
       put is connected to what appears to be an input port on  the
       microprocessor.   The  upshot is that we can affect the scan
       rate without affecting the other  chores  performed  by  the
       microprocessor.

       The modification consists simply of soldering a 470,000  ohm
       resistor  across the leads of resistor R18 on the LOGIC UNIT
       circuit board.

       How was the value of 470,000 ohms  chosen?   Experimentation
       with  different  resistor values showed that for values both
       above and below 470,000 ohms, the R7000 scan rate decreases.
       Not  having  the  R7000 Service Manual, I assume this can be
       explained by the firmware within the microprocessor  associ-
       ated with the scan rate input port.1

       Adding the 470,000 ohm resistor in parallel with R18, rather
       than just replacing R18, has a few advantages:

         1.  The modification is easily undone, returning the radio
             to stock condition.

         2.  The LOGIC UNIT board does not have to be  removed,  as
             would  be the case if R18 was unsoldered from the foil
             side.


                         Making the Modification

       Accessing this circuit board is not difficult, and  involves
       the same steps used when installing the optional Remote Con-
       troller or Speech units.

       Use a towel to cover your work area to avoid scratching  the
       R7000  cabinet.  Unplug the R7000 from the AC line, and turn
       the radio upside down.  Remove the bottom cover by  removing
       the 12 screws holding it in place.

       Remove the 4 screws holding what ICOM terms  the  "partition
       panel".   Pictures  on pages 32 and 34 of the R7000 Instruc-
       tion Manual show the partition panel.  After  removing  this
       panel, the component side of the LOGIC UNIT circuit board is
       accessible.

       Locate R18, a 270,000 ohm 1/8 watt resistor, near  connector
       J5.   You  may wish to remove plug P5 from J5 temporarily if
       it gets in your way.  Carefully solder a 470,000 ohm  resis-
       tor  in parallel with R18.  I used a 1/4 watt resistor as it
       was the smallest on hand.

       Reassemble the radio, connect it to AC  power  and  antenna,
       and enjoy.

       In the modified R7000, the scan and search rates  are  still
       adjustable  using  the SCAN SPEED control.  With the control
       turned fully clockwise (maximum speed), the  modified  R7000
       scans  at  about 13 channels/second and won't miss weak sig-
       nals.


       __________

        1. Perhaps the firmware polls the scan rate input port
           infrequently.  Another possibility is that the scanning
           pulses interrupt the processor, and the interrupt
           firmware is limited in its ability to process frequent
           interrupts.

-- 
==============================================================================
Bob Parnass, AJ9S  -  AT&T Bell Labs  -  parnass@ihlpm.att.com - (708)979-5414
             Don't use "team" as a euphemism for "committee." 
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