PRO-43 ENHANCEMENT
MEMORY EXPANSION & "FADE-AWAY" LIGHT
Brett Bennett 4/12/94
bbb@kuhub.cc.ukans.edu
Copyright 1994 B&D Electronics All Rights Reserved
INTRODUCTION
The following document details two enhancement
modifications that are possible on the Radio Shack PRO-43 scanning
radio. The first modification doubles the factory standard memory
capacity, allowing you to enjoy an additional 200 channels of memory,
plus 10 more monitor memories. After completing the first
modification, it is a fairly simple matter to add a 7 to 10 second delay
feature to the LCD back-light lamp circuit. I designed and performed
these modifications on my PRO-43 and they do work. As I understand
it, there (has been/is being) presented in WORLD SCANNER
REPORT a similar memory expansion. I have not seen this
modification and for all I know it is a better way of doing it. What is
presented is a 'clean-room' design of my own that to the best of my
knowledge is the only one to also offer a time-delay for the LCD back-
light. Having said that, let me say:
I ASSUME NO RESPONSIBILITY FOR ANYTHING THAT
MIGHT HAPPEN TO YOUR RADIO SHOULD YOU OR
ANYONE ELSE ATTEMPT THESE MODIFICATIONS.
WHILE REASONABLE CARE HAS GONE INTO THE
PREPARATION OF THE FOLLOWING DOCUMENT, I CAN
NOT GUARANTEE THAT THERE ARE NOT ERRORS.
The procedure described below is very complicated, and
involves the soldering and desoldering of very tiny components and
the cutting of printed circuit board traces. While the procedure is not
irreversible, it will leave permanent scars inside your scanner. It
should only be attempted by someone with moderate to advanced
electronics experience. I don't think it should be attempted by, to
quote someone else, a "weekend technician." If as you read through
this you feel intimidated by the jargon and required procedures or if an
electronic schematic looks like a strange piece of modern art to you,
then this might not be the 'mod' you are looking for. The following
document will assume you have obtained the materials listed below,
especially the Service Manual, and you have studied the circuit in
some detail. I will not describe in great detail where every component
is or where every solder point on the logic board should be placed.
Having the Service Manual, and having studied the drawings therein
will allow you determine to where it is I refer.
REQUIREMENTS
1 - PRO-43 Service Manual. (Tandy Parts # MS-2000300 - approx.
$6.00)
1 - CD4053 - Triple - SPDT analog switch - Surface mount package
(DigiKey #CD4053BCM-ND - approx. $1.50)
2 - 93C67 EEPROMs (Tandy Parts # MX-8050 - approx.
$13.00/each)
1 - 100k x 5 resistor network. Common lead type. (DigiKey # Q5104)
1 - UN2111 PNP transistor (Q1 on Logic PCB. Tandy Parts # )
1 - 1 uF 16v capacitor.
1 - 10 MOhm 1/8-1/16W resistor.
Misc.:
Wire wrap wire-30 gauge. (Radio Shack)
Grounded soldering iron with approx. 1/32" tip or smaller.
Desoldering Equipment.
Digital Volt Meter. (Used to double check your VCC and Ground
connections, pre-check switching assembly)
Utility knife with fresh sharp small blade. (Needed to cut traces.)
Strong hand held magnifying lens. (Needed to check solder joints.)
+5-10 Volt bench power supply. (Used to check switching assembly.)
Anti-Static work place and grounding wrist band.
Very fine needle nose pliers, wire cutters.
THEORY
When studying the schematic for the PRO-43 one sees that
the channel memory is organized using two 93C67 EEPROMS. As is
common in microcomputer designs, the memory is all connected
together on a common bus, with the individual memory devices being
selected with a Chip-Select (CS) control line. The 93C67 are
particularly simple, in that they are serial devices, only requiring 4
signal lines. (Data In, Data Out, Data Clock and CS) This inspired
me to consider the possibility of adding two more EEPROMs, creating
in effect a second 'bank' of 200 channels. One could then, presumably
with the flip of a switch, choose between the original 200 channels,
and a second bank of 200 channels. (In theory, this could continue to
600, 800, 1000 etc. channels. In practice however, space is very tight
in the PRO-43, and getting anymore memory installed would be very
tricky.)
Switching two CS lines between two pairs of EEPROMs
requires the equivalent of a DPDT switch. While it might be possible
to do this with a mechanical switch, the physical implementation of
this could prove to be very difficult. Rather than use a DPDT switch, I
chose to use a CD4053 triple 2 channel analog
multiplexer/demultiplexer. This CMOS analog 'mux/demux' can be
viewed as a triple SPDT switch. Two sections of the CD4053 are
wired in such a way as to act as a DPDT switch. The advantage being
that a DPDT switch can be controlled with a SPST switch, and no
actively switching digital signal lines need leave the area of the CPU.
At this point one is still faced with the need of a mechanical switch to
control the CD4053, albeit, only a SPST switch is needed. It was
suggested to me by someone on the Internet, that the 'Keylock' switch
might be a good candidate. And indeed it is! While it might be nice,
once in a while, to be able to disable the keyboard, it is more than a
fair trade to give this up for more memory. Thus I used the Keylock
switch to control the DPDT switch made from the CD4053.
Good design dictates that the state of all signal/control lines
are always in a known state. The 93C67's CS lines are active high
leading to the need for pull-down resistors on all 4 CS lines. This
insures that the 93C67's not currently being used will have their CS
lines pulled to ground. I accomplished this with 100K ohm resistors
connected between the CS line and ground. Physically I implemented
this using a resistor array (SIP package) containing 5-100K resistors
all having one common lead. The 5th. resistor is used to pull-down
the CD4053 control lines making up the DPDT switch. This is
necessary when the Keylock switch is in the open position (unlocked)
since the line must be driven low.
This leaves a SPDT switch in the CD4053 not being used.
Studying how the lamp circuit works shows that the keyboard light
switch grounds the base of Q1 to turn on the lamp. Using the CD4053
to act as the switch to ground, and placing a large RC time constant
circuit on the control line of the CD4053 will allow for a time delayed
lamp modification. Because the input impedance of the CD4053 is
extremely high, a small valued capacitor and large value resistor will
work. In my design I used as 1 uF tantalum capacitor and a 10 MOhm
resistor to form the RC time delay. The Pro-43's keyboard light
switch is connected across the capacitor to discharge it when
depressed. This causes the CD4053 to switch on, grounding the base
of Q1. After the switch is released, the capacitor begins to charge
through the 10 MOhm resistor. When this voltage reaches
approximately 1/2 VCC the CD4053 switches off, and the lamp goes
out. (One caveat: When the radio is first turned on, the capacitor is
discharged and therefore a lamp timing cycle will begin with each
power up.)
PROCEDURE
**REMEMBER TO ALWAYS WORK AT A STATIC FREE WORK-
STATION, INCLUDING THE USE OF GROUNDED SOLDERING
EQUIPMENT AND THE WEARING OF STATIC REMOVAL
BRACELETS.**
The first step is to build the switching assembly. To build
this first tin the leads of the surface mount CD4053 and the resistor
array. Following the connections shown in the schematic (figure 1),
attach short (3/8" to 1/2") pieces of wire wrap wire between the 5
resistor leads of RA1-NEW and pins 1,2,3,5, and 9-10 on the CD4053.
(You should always: Size, cut, strip, tin and trim the wire before
soldering it to the CD4053. Doing this makes it fairly easy to get good
solder connections.) Connect the common lead of the resistor array to
pins 6,7,8 and 12 of the CD4053. If done correctly you will have the
resistor array laying flat on its side with its leads facing the CD4053 as
shown in figure 2. This makes the assembly very thin. Inspect the
solder joints with a magnifying glass, and give them a gentle 'tug' to
make sure they are securely soldered. The PCB board drawing on
page 19 of the service manual is an actual size drawing. Check to see
that your assembly will fit into the area just above IC1 and to right of
IC2.
Soldering to the pins of RA1-NEW, connect 4 - 2.5" lengths
of wire to the resistor leads going to pins 1,2,3&5 of CD4053 (This
makes up the 4 switched lines going to the CS pins.) Connect a 5"
length of wire to the resistor pin connected to pins 9&10 of the
CD4053.( This will go to the Keylock switch.) Attach a 2" piece of
wire to the resistor lead attached to pins 6,7,8 & 12 of the CD4053.
(This will be the ground connection.) Attach 3 - 4.5" long wires to
pins 4,15,&16 of the CD4053. These will be the two poles of the
switch and the VCC connection respectively. Finally attach 2 - 5"
wires to pins 11 & 14 of the CD4053 if you intend to also add the
lamp timer modification. At this point you should have a strange
looking device with 11 wires sticking out of it. DOUBLE CHECK
YOUR WORK AND SOLDER JOINTS AT THIS POINT.
The next step is to check the operation of the switching
assembly. Using a 5-10 volt power supply, apply power to the
assembly. Using a DVM, check to see that there is continuity between
pins 4&5 and pins 15&2 while the control line (the wire attached to
pins 9&10) is not connected to anything. And also check to see there
is NO continuity between pins 4&3 and 15&1. If that checks, attach
the control line to VCC. There should then be continuity between pins
4&3, and 15&1 and no continuity between 4&5 and 15&2. Next
check for continuity between pin 14 and ground when pin 11 is
grounded. The resistance between 14 and ground should become
infinite when pin 11 is then connected to VCC. After check-out put
the assembly aside in a static proof container.
Using extreme care bend all the leads, EXCEPT FOR PIN 3,
of one of the 93C67 so that they are pointing as straight DOWN as
possible . Bend pin 3 so it is sticking straight out from the body of the
chip. These leads are very fragile and I suspect they will only accept a
single bending before breaking,. After the leads are bent, carefully tin
all leads. Put the EEPROM back in its carrier, and repeat on the
second EEPROM. The next step is to prepare the scanner for the
switch assembly. From here on out, "The cheese becomes more
binding," so work carefully and think about everything twice before
doing it!
Remove the battery compartment lid and battery. Remove the
4 case screws and the back of the case. Disconnect the two wire
connectors on the RF board. Desolder the antenna feed line and its
ground connection. Remove the 6 screws holding down the RF board
and remove it from the audio board. Disconnect the speaker wire from
the audio board, and remove the 2 screws holding it to the front of the
case. Separate this from the front of the case. Desolder and remove
the RF-shield from the logic board. Wash your hands to remove as
much skin oil as possible! Remove the screws holding the logic PCB.
Turn the unit over, and with your hand supporting the PCB lower it
from the case front. The reason for this is that the LCD assembly will
stay with the board. If during this process the LCD and its backing
glass do separate, handle them as little as possible. Also note the
back-glass has a white frosted side. The frosted side, the light diffuser,
is placed away from the LCD panel. Remove the rubber keypad, and
locate the two traces running to the Keylock switch. Using a sharp
utility knife, cut both of these traces near the switch, examine the cuts
with a magnifying lens to make sure the switch is severed from the
rest of the board. Avoid touching the keypad contact area as much as
possible. Checking to make sure dust has not entered the LCD view
area, put the logic PCB back in the front of the case and secure it with
its screws.
Locate IC2 and IC3 EEPROMs on the logic board. Add to
each of the pins on both chips a small amount of solder. This will be
necessary to attach the new EEPROMs. Of course you must make sure
that you form no solder bridges. At this stage I suggest you re-install
the audio board and RF board. (There is no need to solder the RF
shield back on, nor should you resolder the antenna connections.) By
holding the battery in place and slipping the battery lid into proper
position, it is possible to power up the radio without bothering with the
case back. Check to see that all keys are functioning correctly except
for the Keylock switch, and that the display looks normal. You are
now ready to begin the 'fitting' of your switch assembly into the radio.
Locate the area just above IC1 and to the right (as being
viewed from the backside of the radio) of IC2&3. There is a relatively
open space here where the CD4053 and resistor array can lay. Cut a
piece of thin card board stock to be slightly larger than the area taken
up by the switch assembly. This will serve as an insulator between the
logic PCB and the assembly. Keeping the assembly in its final
position, start sizing the lengths of the wires. The wires connected to
pins 1&2 of the CD4053 must reach IC3 pin 3, and the wires on pins
3&5 of the CD4053 must reach IC2 pin 3. Remember when cutting
these down to leave enough extra wire for stripping, tinning and final
trimming. The wire connected to pin 15 of the CD4053 must be long
enough to reach the TRACE on the PCB going to IC3 pin 3. Likewise
the wire on pin 4 of the CD4053 must reach the trace running to IC2
pin 3. The switch control wire (pins 9&10 of the CD4053) must reach
down to outside most solder pad on the Keylock switch. VCC, pin 16
of the CD4053, is sized to reach the 82 ohm resistor R26 located next
to Q1. The ground connection can be made on the large copper area
under the switch assembly after scraping a small area of solder-mask
off. After the wire lengths have been determined, strip and tin the
ends of all the wires and set the assembly aside.
Using a sharp knife, cut the trace running from IC1 to pin 3
of IC2. Repeat this for the trace running from IC1 to pin 3 of IC3. On
either side of the cuts, scrape off a 1/8" area of solder mask and tin the
exposed copper. Be careful not to damage any of the surrounding
traces or components. Place the switching assembly in its proper
location and solder the ground wire to the solder-mask free area you
made near IC1. Attach VCC (pin 16 of the CD4053) to the top of
R26. Attach the pin 5 wire to the cut trace that runs to IC2-pin 3, and
attach the pin 2 wire to the cut trace running to IC3-pin 3. Next attach
the wire on pin 4 of the CD4053 to the trace running to pin 18
(previously running to IC2-pin 3) of IC1. Likewise connect the wire
on pin 15 to the trace connected to pin 19 (previously running to IC3-
pin 3) of IC1. If done correctly you now have 4 wires running to the
four 'new' connection points made by cutting the two CS line traces.
Connect the wire tied to pins 9&10 of the CD4053 to the outside (left
side) conductor of the Keylock switch. Attach a new piece of wire to
the center conductor of the Keylock switch. Size and connect the other
end of this wire to center lead of IC5. (IC5 is low battery detector for
the CPU. The center lead of this is connected to 5 volts which is
sufficient to switch the CD4053. Later we will need to attach another
connection to R26, and squeezing 3 wires to this single point would be
tight so I used the 5 volt bus for switching.)
Place the insulator under the assembly and tape a corner in
place so it will not move. Cut another cardboard insulator big enough
to cover the switching assembly, and place this on top of the logic
PCB. Bending the currently disconnected wires (pins 1,3,11,&14) in
such a way that they don't short to anything (or each other) , install the
audio board back in to the radio. Install the RF board and prepare to
power up the radio. Making sure the Keylock switch is in the
UNLOCKED position, turn the radio on. It should begin to scan
normally. (Believe me you will breathe a big sigh of relief when it
does!) Turn the radio off, move the Keylock switch to LOCKED
position and turn the radio back on. You should see it either scanning
frequency 000.0000 or the frequency field will be blank, with the
channel counter incrementing. After a few seconds, the frequency
number always blanked out and the am/fm indicators blinked
randomly on my radio. If you are unable to make the radio scan
correctly, there is something wrong with the switch assembly or your
connections.
The next step is to install the new memory. The leads on the
new memory are not long enough to reach the leads of the factory
memory. Trying to solder bridge the gap is difficult accomplish
without also bridging adjacent pins. The best way I found to do this is
to use tinned wire wrap wire. So the first step here is to tin about 6" of
stripped wire wrap wire. Remove one of the new 93C67s from its
carrier and place it on top of IC2, making sure that the extended pin 3
is over pin 3 of IC2. Put a droplet of solder on the tip of your
soldering iron. While holding down the memory with a finger, apply
the soldering iron to one of the corner pins of both ICs. The droplet
should 'jump' over the gap between the pins and solder them together.
Check both sides of the EEPROM to insure that all pins are accurately
aligned. For the remaining straightened pins, proceed as follows:
While holding the tinned wire wrap wire against the lower
and upper pins, apply a freshly cleaned soldering iron tip to the gap
area of the joint. The extra solder you earlier placed on the factory
EEPROM will then be available to flow along the wire and solder to
the pin of the new EEPROM. CHECK the joint with a magnifying
lens. After a visual conformation of the joint, clip the wire close to the
pin of the newly installed memory. If you like go back to the first pair
you soldered and lay the wire into the molten solder. Repeat for IC3.
Attach the wire connected to pin 3 of the CD4053 to pin 3 of
IC2-NEW, and connect the pin 1 wire to pin 3 of IC3-NEW. Install
the cover insulator over the switch assembly and prepare for a power
up. With the Keylock switch in the Unlocked position power up the
receiver. After insuring that the factory memory is still working
correctly, power down, switch to the Locked position and power up
again while holding down the 0 key and the Clear key. You should
now see the radio scanning frequency 000.0000 for all 10 banks
repeatedly. Press the PGM key to stop scanning and enter a valid
frequency value and press enter. Press PGM, then the DOWN-
ARROW, then PGM again. The frequency you just programmed
should now be on the display. (At this point feel free to cheer! YOU
have just added 200 more channels to your PRO-43. The next step
will be the icing on the cake!)
This next step requires you to lift the BASE of Q1 from the
logic PCB. (I found this to be very difficult, in fact, I ended up
destroying Q1. Thus the extra Q1 in the parts list.) Desolder and lift
the Base lead of Q1 from the logic PCB. Solder together one lead of
R2, the positive terminal of C1 and the wire from pin 11 of the
CD4053. Also from this junction, connect a wire to the solder pad on
the logic PCB where Q1's base was connected. The area to the right of
the Keylock switch provides a space where these components can lay.
Connect the base of Q1 to the wire connected to pin 14 of the CD4053
switch assembly. The other end of R2 is connected by wire to the top
of R26, this provides the charging voltage for C1. The negative lead
of C1 can be connected to the RF shield ground pad near the Keylock
switch. (Check that the RF shield will fit in place over C1. If it will
not, place C1 so that its body is just below the bottom of the shield.
Insulate the R2-C1 combination with electrical tape. Tape the switch
assembly's top insulator cardboard in place and install and solder the
RF-shield back onto the logic PCB. Prepare the radio for bench power
up.
Turn the radio on, the lamp should come on. After 7 to 10
seconds the lamp should go out. Check in a darkened room to insure
that the lamp completely extinguishes. Depress the light switch on the
keyboard. The lamp should immediately light, and stay lit for 7 to 10
seconds after it is released. Install all the remaining screws for the RF
board, solder the antenna lead and ground connections, and replace
the case back.
USAGE
The light feature is self explanatory, and quickly finds itself
useful in darken conditions. As noted earlier an unfortunate side-
effect of the lamp circuit design is that the lamp will illuminate for 7
to 10 seconds every time the scanner is first turned on. (Maybe this is
a feature to some.) Switching between active banks requires a little
more thought. The safest way of changing banks is to: Turn the
scanner off, switch banks, and then turn the scanner back on. But
sooner or later you will switch banks while the scanner is on. When
this happens you will see a curious event. The radio's CPU will
continue to scan from the previously selected banks, but the
frequencies scanned will now be those from the on-line EEPROM.
This makes sense, since the CPU has no knowledge that its memory
resources have been changed. Pressing the Manual button, followed
by the Scan button, will cause the CPU to reload the scan banks that
were last saved in the currently selected EEPROMs. Also any monitor
frequencies that were stored are recalled. This allows you to set up
two different frequency configurations, one in each bank of EEPROM.
To change between them on the fly, just flip the Keylock switch, press
the manual button, followed by the scan button. The only time I can
foresee there being a problem is if some how one were to flip the
switch while the CPU was doing a write to EEPROMs. Keeping this
in mind you should never have any problems.
There are a couple of 'gotch-ya' that can happen when
switching memory banks without cycling power. The PRO-43 loads
the list of all locked-out channels only when it is first powered up.
(This makes sense if you think about it. While I don't know for a fact,
I assume that the Lock-out information for each channel is stored
together with that channel's frequency in the EEPROM. If the CPU
didn't pre-load the list of locked out channels, it would have to
constantly re-read each channel to determine its lock-out status.) The
side-effect of this is that it can cause the radio to appear to be
randomly locking and unlocking channels when switching memory on
the fly. The only realistic solutions appear to be to either cycle power
when you switch memory banks, or use Lock-outs very sparingly. The
Priority channel assignment is also loaded only when power is first
applied. This can make the radio start checking the wrong frequency
when memory is switched and the priority feature is used. The best
way around this problem seems to be to assign the same channel
number to be the priority channel in each memory bank.
CONCLUSION
Performing the described modification will provide the owner
of an already excellent hand-held scanner, the convenience of a total
of 400 channel memories and 20 monitor locations, doubling the
factory capacity for under $40.00. It also provides a "fade away" LCD
back-light with a 7 to 10 second delay. The bank switching nature of
the design allows for the user to program two unique 'personalities'
into the scanner selecting between them with the Keylock switch. The
modification while complicated can be performed by any person with
moderate to advanced electronics experience.