From: parnass@cbnewse.cb.att.com (Bob Parnass, AJ9S)
Subject: Re: BC200xlt battery mod: not required??
Organization: AT&T Bell Laboratories, Naperville, IL
Distribution: usa
Date: Fri, 8 Jan 1993 14:05:12 GMT
Summary: conservative battery warning ckt bad in EARLY 200xlts only

In article 3088, kevin.jessup <kevin.jessup@mixcom.mixcom.com>
cited this article:

 >    *****************************************************
 >    ALL USERS OF THE BEARCAT 200-XLT HANDHELD SCANNER HAVE PROBABLY HAD
 >    PROBLEMS CONCERNING SHORT BATTERY PACK LIFE.  BATTERY INDICATOR COMES
 >    ON TOO SOON........

The out of tolerance Zener diode in the low battery warning circuit
was troublesome in *EARLIER* vintage 200xlts.  It's *NOT* a problem
in all 200xlts.

 > The unit's date of manufacture code indicates that it was made in July
 > of 1992.

That Zener diode shouldn't be a problem in your scanner.

To determine if the battery warning ckt is too conservative,
power the 200xlt with a good, adjustable voltage, regulated DC power
supply instead of the NiCd.   Use an accurate digital voltmeter to
monitor supply voltage.  Start with the supply adjusted to
7.2 volts and gradually decrease the voltage.  If the warning
circuit activates above 6.0 volts, I'd say it's too conservative.

The Uniden battery pack contains 6 AA cells.  A NiCd cell is about
out of gas when it's voltage is below 1 volt.

Kevin, it sounds like either you have a bona fide battery or
charging problem or are expecting too long a life between
recharges.


 > Well, that was simple enough to do (and un-do).
 > 
 > But...it made no difference that I could tell and I am certain I shorted
 > out the correct zener diode.  (I have the 200xlt service manual and I
 > used to work as an electronics tech.)
 > 
 > So here's the problem...
 > 
 > Just before doing the mod, I let the scanner run till the flashing low
 > battery indicator came on.  I then let it continue to run till the CPU
 > shut the unit down.
 > 
 > I immediately removed the battery and performed the mod.  (It took only
 > 5 minutes).  I reassembled the unit and attached the battery.
 > 
 > As expected, the unit turned on and there was no low battery indicator.
 > Unfortunately (and to my surprise) the unit ran only 3 more minutes till
 > the audio output became so scratchy sounding that it was unreadable.  This
 > was at a low volume setting too.
 > 
 > It seems to me that the diode mod was not needed and that, in fact, the
 > zener diode used in the unit  was at a proper voltage for correct low
 > battery detection.  The unit and the battery are in near-new condition.
 > The unit's date of manufacture code indicates that it was made in July
 > of 1992.
 > 
 > Could it be that Uniden has corrected the problem (an improper zener
 > diode, or associated comparator circuitry) with the newer units??
 > 
 > BTW, the Uniden service manual does not list the zener's voltage but
 > does give a number: HZK3CLL01-TR.  The schematic DOES list test points
 > at either end on the zener.  These voltages are shown as 7.8 (at the
 > cathode) and 4.5 (at the anode).  This gives a zener voltage of 3.3V.
 > Can anyone confirm these numbers on older versions of the service
 > manual?
 > 
 > -- 
 > Kevin Jessup, kevin.jessup@mixcom.mixcom.com
 > 
 >         "Friends don't let friends run DOS."
 >                           -- Microware
 > 
 > 
-- 
==============================================================================
Bob Parnass, AJ9S  -  AT&T Bell Labs  -  parnass@ihlpm.att.com - (708)979-5414