

Article 13545 of rec.ham-radio:
Path: philabs!philmtl!uunet!ginosko!gem.mps.ohio-state.edu!tut.cis.ohio-state.edu!att!cbnewsc!parnass
>From: [email-masked] (Bob Parnass, AJ9S)
Newsgroups: rec.ham-radio
Subject: Longer battery life for the Regency MX-4200/MX-4000
Keywords: scanner radio, NiCd battery charging
Message-ID: <[email-masked]>
Date: 18 Aug 89 19:16:57 GMT
Organization: AT&T Bell Laboratories
Lines: 100
Posted: Fri Aug 18 15:16:57 1989

x
              GET LONGER BATTERY LIFE FROM YOUR
              REGENCY MX-4000 OR MX-4200 SCANNER

                   by Bob Parnass, AJ9S

   The discontinued Regency MX-4000 and MX-4200 are  battery
   operated,  20  channel  scanners manufactured in Japan by
   AOR.  Both scanners contain a low battery warning circuit
   which disables the scanner when the battery voltage falls
   below a preset level.

   A freshly charged battery pack should  last  at  least  5
   hours  before  needing  a  recharge.   Ron  Smithberg, of
   Joliet, IL, complained of getting only 2 hours use from a
   set  of  freshly  charged  NiCd batteries in his MX-4200.
   This article describes how we increased his usage to over
   7 hours between charges.

   Both MX models are powered by a pack of 4 AA  sized  NiCd
   batteries.   The  battery pack is nominally 4.8 volts and
   has a rated capacity of about 500 mAh.  The scanner draws
   about  100  mA  when  squelched.  A good rule of thumb is
   that a NiCd should be recharged when  its  voltage  falls
   below  1.0 volts per cell.  Using this heuristic, the MX-
   4200 battery pack should be recharged when it falls below
   4.0 volts under load.

   The low battery circuit on Ron's MX-4200 was  misadjusted
   to  shut  down  the  scanner prematurely when the battery
   voltage fell below 4.7 volts.  I readjusted the low  bat-
   tery threshhold to 4.0 volts.

   You can use the same procedure, but  you  will  need  the
   following equipment:

      o An adjustable, regulated DC power supply, capable of
        furnishing between 3 and 5 volts at 500 mA or more.

      o An accurate means  of  measuring  voltage  from  the
        power  supply.  A digital voltmeter with an accuracy
        of 5% or better is preferred.

      o A #1 Phillips screwdriver.

      o A Small, slotted screwdriver or alignment tool.

   The low battery sensor  threshhold  is  controlled  by  a
   potentiometer.   Here's how to readjust the sensor to 4.0
   volts:

    1.  Turn the scanner off.
    2.  Connect a digital voltmeter  to a well regulated  DC
        power supply and adjust the supply to 5.0 volts.
    3.  Connect the power supply to the  snap  terminals  on
        the  scanner that would normally connect to the bat-
        tery pack.  Be  sure  to  observe  proper  polarity.
        Connect  the  positive  lead  of  the  supply to the
        female snap, and the negative lead to the male snap.
    4.  Turn the scanner on.
    5.  As you watch the scanner's  LCD  display,  gradually
        reduce  the power supply voltage until the scanner's
        low voltage warning begins to flash.
    6.  Read the digital voltmeter.  If it reads between 3.9
        and  4.0  volts,  no further adjustment is required,
        just disconnect the supply and reconnect the battery
        pack.
    7.  Otherwise, turn off and disconnect the power supply,
        and continue.
    8.  Turn the scanner upside down, and place it on a soft
        cloth so as not to scratch the case.
    9.  Remove the bottom tilt foot from the scanner.
   10.  Remove the battery pack.
   11.  Remove the 4 Phillips screws holding the  case  bot-
        tom, then remove the case bottom.
   12.  Reconnect the power supply to the scanner and set it
        to 4.0 volts.
   13.  Turn the scanner on.
   14.  Locate a small gray  potentiometer  on  the  printed
        circuit  board.   The  potentiometer looks something
        like a gray plastic Phillips  screw  head.   If  the
        scanner  front  panel is facing you, the pot will be
        just behind the keyboard on the  left  side.  (Don't
        confuse  this  pot  with  the 3 pots along the right
        edge of the board.  The battery voltage  sensor  pot
        is not near any other pot.)
   15.  Slowly adjust the potentiometer to the threshhold at
        which the low battery indicator begins to flash.

   This procedure worked with great success on  an  MX-4200,
   and its battery life was increased from 2 to 7.5 hours.

   I would like to thank Rick Meyer, WB9UFL, for finding the
   potentiometer  in his MX-4000, and Ron Smithberg for let-
   ting me experiment with his MX-4200.

-- 
============================================================================
Bob Parnass, AJ9S - AT&T Bell Laboratories - att!ihuxz!parnass (312)979-5414