The BC2500XLT is officially discontinued as a product. However,
due to the requirements of FCC Part 15.121 subpart A , Uniden
modified the production of the BC2500XLT on its last production
run. This model can not be modified to pick up cellular reception.
All previous units should be modifiable. You can tell if your
BC2500XLT is non-modifiable by checking the date code on the back
plate of the scanner. If the date code reads "OGID"
(7/94) then the unit is not modifiable. If anyone finds
this not to be true or has other information about this scanner,
please contact me at the email address at the bottom of this document.
This set of instructions describes the procedures to modify the
BC2500XLT handheld scanner to pick up the deleted cellular range
of frequencies. After performing this modification, the BC2500XLT
will have continuous coverage from 760 to 1300 MHz. In addition,
when searching in the cellular bands, the scanner will step in
the appropriate 30 KHz steps.
You should have a low-wattage soldering iron with a fine tip,
a small, slotted screwdriver, a maginfing glass, and a bright
light. It also helps to have steady hands!
Taking the case apart
First, remove the antenna and battery pack. Remove the two black
screws on the back of the scanner. These are on either side of
the belt clip. Also remove the two silver screws at the bottom,
"under" the battery pack. Put these parts in a safe
The case is held together by friction tabs. They are tight along
the sides, right at the top of the battery compartment. Try using
a small slotted screwdriver and slide it down the sides of the
scanner in the groove. With a little (very little) force, you
should able to snap open the case. Try not to damage the plastic.
Lay the scanner down on its face (on a soft surface) and carefully
pull the back plastic cover off. The back cover comes off about
3/4 of an inch below the top of the scanner. The piece of plastic
the molds over the top back of the scanner (the piece that has
the speaker and headphone jacks stays on.)
Removing the circuit boards
You'll see three circuit boards stacked on top of each other.
The top two are held together by silver brackets on either side
of the boards. Take your slotted screwdriver and slide it under
the edge of one of the silver side bracket at the bottom. Then
use the screwdriver to pry up gently. This will lift the double-board
and lift the pins out of the black, 11-pin molex connector that
is part of the bottom (third) board.
Lift the double-board circuit board "sandwhich" by the
brackets and completely disconnet the molex connector. Now, the
plastic part of the case on the top will separate from the front
of the scanner. It may stick a little because there are friction
tabs on either side of the volume/squelch knob. Apply a downward
pressure to the top of the scanner (at the knobs) if it is sticking.
Lift the entire sandwhich up. It is connected by a ribbon cable
to the bottom board. Be careful not to stretch the ribbon connector
as you lay the board along side the radio.
Performing the mod
You now need to locate the microprocessor chip. It's the biggest
IC chip on the bottom board. It is labeled "Uniden UC-1513A."
With the scanner in a normal "antenna-to-the-top" orientation,
you'll find a group of surface-mounted resistor chips below the
microprocessor. These chips are tiny! About the size of
a large grain of pepper. However, if you look at them with a magnifier,
you'll see that they're labeled "104."
There are two rows of SM resistors. The top row has two chips
and the botton row has three (see the diagram below).
To perform the actual modification, you need to unsolder the left-most
chip in the bottom row (labeled "R" in the diagram).
To unsolder the chip, place your small-tipped soldering iron against
the left or right edge of the chip and apply a slight pressure.
The combination of heat and pressure will unsolder the chip and
slide it off it's pad. You will want to move it with your tweezers
to the open pad to its immediate left (labeled "X" in
the diagram) and solder it back in place. The hardest part will
probably be placing the resisitor on the new pads and keeping
it there while you resolder it.
| | | | | UC-1513A | | | | | Legend: |Number of pins on diagram may be wrong.| p = solder pad |Make identification by resistor matrix.| c = a component | | R = resistor to move ----------------------------------------- X = new location | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | ---------| | | | | | | | | | | --------| | | | | | | | | | | --------| | ----- | | | ---- | | \ | | | / \ | | \ p | p-c-p p | p-c-p | / | / / / | | | | | / | / | / | p X p-R-p p p-c-p p-c-p p ^ ^ | |-Move resistor "R" to the left to "X"
Reassembling and testing
Next, reassemble the scanner. Start by placing the molex pins
in the connector and then put the circuit boarrd unit back in
Close up the case.
You can test the mod by entering 869.000 MHz and then pressing
the LMT key. Then enter 894.000 and press LMT again. Finally
press the SRC key. The scanner should start searching,
however, there is a good chance it will be searching in improper
steps. To make it search in the correct 30 KHz steps, press the
decimal key twice. This sets the increment to 30 KHz. However,
nothing appears in the display for the step increment, since the
BC2500XLT doesn't use this increment for any other range.
Note, however, that there is a birdie at 870.39 MHz. In addition,
the BC2500XLT may lock up on other frequencies in the cellular
range and lock up on the digital contral channels. To get a continuous
search, you may have to constrain the range to be less than the
full cellular base range.
Watching this thing search through cellular at 100 cps is awesome!
Good luck and have fun!
Thanks to Bob Grove for the first description of this mod and
to Russell Keating for the ASCII diagram!