Classic Bearcat 855XLT 800mzh Scanner
The Bearcat 855XLT is one of Uniden's "classic" scanners - no longer made but still in demand today - especially the earler ones manufactured before 1994. These early, desirable Bearcat 855XLTs are becoming very hard to find on the used market today.
Summary:
According to Marc Saxon in "Scanner Scene" in Popular Electronics,
November, 1995 the BC-200XLT, BC-205XLT, and BC-950XLT are all
modifiable. The BC-2500XLT can be modified if the manufacturing code on
the unit does not end in OBID, other codes ending in D are ok. The
BC-700A, BC-700XLTA, BC-760XLT, BC-855XLT, and BC-890XLT are all
modifiable if the manufacturing code on the unit does not end in D. No
other Bearcat scanners can have their cellular reception unblocked.
I purchased a BC855XLT and successfully modified
it by simply experimenting. The date code does NOT end in a D. This
document contains the results of my experiments with this scanner.
Before Modification After Modification
29 - 54 MHz 29 - 54 MHz (or 66 - 88 MHz)
108 - 174 MHz 108 - 174 MHz
406 - 512 MHz 406 - 512 MHz
806 - 956 MHz (cellular blocked) 806 - 956 (continuous)
50 channels 5 banks of 10 each 100 channels 5 banks of 20 each
Keyboard Hacks:
I tried all 385 possible combinations of three keys held down while
turning on power. Only three significantly different behaviors were
discovered:
MANUAL-0-E Load test frequencies
SCAN-0-E Clear all channels to frequency 000.000
Mark all channels as locked out
Clear the search frequency limits
(forget) Clear all channels to frequency 000.000
Mark all channels as NOT locked out
Clear the search frequency limits
(if anyone -really- thinks this is a useful
feature, I have written down somewhere what keys
these were and could look them up)
Hardware Hacks:
First, unplug the power from the back of the case, and remove any
antenna connection. Turn the unit over. Carefully remove the five
screws holding the case closed. As you open the unit, be careful as
there are thin wires connecting circuit boards on the top of the case
(the microprocessor/control board) and the bottom of the case (the
receiver proper). The wires leading to the speaker should be
disconnected (be sure to pull on the connector, not on the wires).
Now lay the botttom of the case on the left, and the top of the case on
the right, with the circuit boards uppermost, and the back of the case
(with the power and antenna connectors) away from you. Look carefully
at the microprocessor board (on the right) and locate the parts and
jumpers as shown on the diagram.
(s) +-----------------------------------------------+
| (wires) (wires) | +-------+ |||||| Jumpers |||||||| |
| D201 |||||| 12345 |||||||| |
| | |||||| ||||| |||||||| |
| V |||||| ||||| |||||||| |
| - |||||| ||||| |
| | |
| |
| |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| |
+-------------------------------------------------------+
In this diagram, (s) represents the speaker, (wires) means several
colored wires going to the other board, D201 is a diode marked D201 on
the board, and Jumpers 12345 means bare wire jumpers which I
(arbitrarily) numbered 1 through 5. The tildes (~) represent a large
section of the board which is not depicted.
Each jumper has two ends. The end near where I have Jumpers and 1-5
marked on the diagram I will call the "top". The other end (down toward
the rest of the board, or the front of the case) I will call the
"bottom". The "bottom" end of each jumper can either be connected
across the top of the board (the way it is shipped) or to an alternate
pad located on the underside of the board. Look below and determine
which of the options you wish to change, and move the corresponding
jumper to the alternate connection point.
Carefully remove the (was it 11?) screws holding the processor board to
the top of the case. Carefully remove the processor board, and turn it
over, from right to left. This leaves the notch for the speaker at the
"upper right". You can now locate the pads underneath the jumpers. Each
jumper passes through the board, and is soldered to a pad. Just above
these pads are other pads, one for each of the jumpers which I numbered
2 through 4. To change the state of any of these four jumpers, cut the
jumper on the top side of the board, and jumper the "bottom" end to the
corresponding pad on the underneath side of the board, thereby
connecting it to its alternate location. Remember that the jumpers are
now numbered 54321 from left to right.
Jumper Connection Effect
------ ---------- ------
2 Across Top enables 806-960 MHz frequencies
Underneath disables 806-960 MHz frequencies
3 Across Top enables 29-54 MHz, disables 66-88 MHz
Underneath enables 66-88 MHz, disables 29-54 MHz
4 Across Top enables 50 channels 5 banks of 10 each
Underneath enables 100 channels 5 banks of 20 each
5 Across Top disables cellular frequencies
Underneath enables cellular frequencies
The reception on 66-88 MHz was nothing spectacular, but it was ok.
Probably changing some coils in the front end would improve reception.
One could add a switch to change this at will. But note that I found
that modifying any of the jumpers cleared all frequencies when the
processor was next powered up.
I don't suppose anyone wants to completely -disable- all 806-960 MHz
reception, so I'll assume that you will perform the modifications to
jumpers 4 and 5, possibly 3. This table summarizes the results:
Before Modification After Modification
29 - 54 MHz 29 - 54 MHz (or 66 - 88 MHz)
108 - 174 MHz 108 - 174 MHz
406 - 512 MHz 406 - 512 MHz
806 - 956 MHz (cellular blocked) 806 - 956 (continuous)
50 channels 5 banks of 10 each 100 channels 5 banks of 20 each
Turn the processor board back over, and carefully rethread the screws
which hold down the board into the holes, and tighten them. It is best
to turn them backwards in the holes until the threads re-engage. If you
do not do this carefully, you will soon have holes which take a larger
size screw. You have been warned. Also do not overtighten. Tighten only
enough so that the board is held snugly.
Now fold the case back together, and re-attach the speaker wire. The
connector only goes back one way. Be sure not to pinch any wires
between the halves of the case. Also watch for bundles of wires wrapped
around or stuck between the volume and squelch controls.
Carefully insert and tighten the five screws holding the case together,
following the instructions listed above for the screws holding the
processor board. Reattach the antenna and power supply.
Disclaimer:
Intercepting transmissions in the cellular band is illegal.
The reader is responsible for determining the suitability of attempting
modifications.
In other words, you are responsible for whatever you do to or with your
scanner, and I am not.
Concerning Modifications of the
Uniden Bearcat 855 XLT scanner:
Summary:
According to Marc Saxon in "Scanner Scene" in Popular Electronics,
November, 1995 the BC-200XLT, BC-205XLT, and BC-950XLT are all
modifiable. The BC-2500XLT can be modified if the manufacturing code on
the unit does not end in OBID, other codes ending in D are ok. The
BC-700A, BC-700XLTA, BC-760XLT, BC-855XLT, and BC-890XLT are all
modifiable if the manufacturing code on the unit does not end in D. No
other Bearcat scanners can have their cellular reception unblocked.
I purchased a BC855XLT and successfully modified
it by simply experimenting. The date code does NOT end in a D. This
document contains the results of my experiments with this scanner.
Before Modification After Modification
29 - 54 MHz 29 - 54 MHz (or 66 - 88 MHz)
108 - 174 MHz 108 - 174 MHz
406 - 512 MHz 406 - 512 MHz
806 - 956 MHz (cellular blocked) 806 - 956 (continuous)
50 channels 5 banks of 10 each 100 channels 5 banks of 20 each
Keyboard Hacks:
I tried all 385 possible combinations of three keys held down while
turning on power. Only three significantly different behaviors were
discovered:
MANUAL-0-E Load test frequencies
SCAN-0-E Clear all channels to frequency 000.000
Mark all channels as locked out
Clear the search frequency limits
(forget) Clear all channels to frequency 000.000
Mark all channels as NOT locked out
Clear the search frequency limits
(if anyone -really- thinks this is a useful
feature, I have written down somewhere what keys
these were and could look them up)
Hardware Hacks:
First, unplug the power from the back of the case, and remove any
antenna connection. Turn the unit over. Carefully remove the five
screws holding the case closed. As you open the unit, be careful as
there are thin wires connecting circuit boards on the top of the case
(the microprocessor/control board) and the bottom of the case (the
receiver proper). The wires leading to the speaker should be
disconnected (be sure to pull on the connector, not on the wires).
Now lay the botttom of the case on the left, and the top of the case on
the right, with the circuit boards uppermost, and the back of the case
(with the power and antenna connectors) away from you. Look carefully
at the microprocessor board (on the right) and locate the parts and
jumpers as shown on the diagram.
(s) +-----------------------------------------------+
| (wires) (wires) | +-------+ |||||| Jumpers |||||||| |
| D201 |||||| 12345 |||||||| |
| | |||||| ||||| |||||||| |
| V |||||| ||||| |||||||| |
| - |||||| ||||| |
| | |
| |
| |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| |
+-------------------------------------------------------+
In this diagram, (s) represents the speaker, (wires) means several
colored wires going to the other board, D201 is a diode marked D201 on
the board, and Jumpers 12345 means bare wire jumpers which I
(arbitrarily) numbered 1 through 5. The tildes (~) represent a large
section of the board which is not depicted.
Each jumper has two ends. The end near where I have Jumpers and 1-5
marked on the diagram I will call the "top". The other end (down toward
the rest of the board, or the front of the case) I will call the
"bottom". The "bottom" end of each jumper can either be connected
across the top of the board (the way it is shipped) or to an alternate
pad located on the underside of the board. Look below and determine
which of the options you wish to change, and move the corresponding
jumper to the alternate connection point.
Carefully remove the (was it 11?) screws holding the processor board to
the top of the case. Carefully remove the processor board, and turn it
over, from right to left. This leaves the notch for the speaker at the
"upper right". You can now locate the pads underneath the jumpers. Each
jumper passes through the board, and is soldered to a pad. Just above
these pads are other pads, one for each of the jumpers which I numbered
2 through 4. To change the state of any of these four jumpers, cut the
jumper on the top side of the board, and jumper the "bottom" end to the
corresponding pad on the underneath side of the board, thereby
connecting it to its alternate location. Remember that the jumpers are
now numbered 54321 from left to right.
Jumper Connection Effect
------ ---------- ------
2 Across Top enables 806-960 MHz frequencies
Underneath disables 806-960 MHz frequencies
3 Across Top enables 29-54 MHz, disables 66-88 MHz
Underneath enables 66-88 MHz, disables 29-54 MHz
4 Across Top enables 50 channels 5 banks of 10 each
Underneath enables 100 channels 5 banks of 20 each
5 Across Top disables cellular frequencies
Underneath enables cellular frequencies
The reception on 66-88 MHz was nothing spectacular, but it was ok.
Probably changing some coils in the front end would improve reception.
One could add a switch to change this at will. But note that I found
that modifying any of the jumpers cleared all frequencies when the
processor was next powered up.
I don't suppose anyone wants to completely -disable- all 806-960 MHz
reception, so I'll assume that you will perform the modifications to
jumpers 4 and 5, possibly 3. This table summarizes the results:
Before Modification After Modification
29 - 54 MHz 29 - 54 MHz (or 66 - 88 MHz)
108 - 174 MHz 108 - 174 MHz
406 - 512 MHz 406 - 512 MHz
806 - 956 MHz (cellular blocked) 806 - 956 (continuous)
50 channels 5 banks of 10 each 100 channels 5 banks of 20 each
Turn the processor board back over, and carefully rethread the screws
which hold down the board into the holes, and tighten them. It is best
to turn them backwards in the holes until the threads re-engage. If you
do not do this carefully, you will soon have holes which take a larger
size screw. You have been warned. Also do not overtighten. Tighten only
enough so that the board is held snugly.
Now fold the case back together, and re-attach the speaker wire. The
connector only goes back one way. Be sure not to pinch any wires
between the halves of the case. Also watch for bundles of wires wrapped
around or stuck between the volume and squelch controls.
Carefully insert and tighten the five screws holding the case together,
following the instructions listed above for the screws holding the
processor board. Reattach the antenna and power supply.
Disclaimer:
Intercepting transmissions in the cellular band is illegal.
The reader is responsible for determining the suitability of attempting
modifications.
In other words, you are responsible for whatever you do to or with your
scanner, and I am not.