Modifying the PRO-43

Copyright 1992, 1996 by Howard Bornstein  
(Revised: October 18, 1994)
(Revised: August 8, 1996)  

This document may be freely distributed for all non-commercial purposes as long as it is distributed unchanged and complete.

This document describes how to perform three modifications to the stock PRO-43 Scanning Receiver. These mods will:  

o Restore the base and mobile cellular bands in the 800 MHz range
o Restore the 54-88 MHz range
o Drastically reduce the volume of the PRO-43 beep sound  

When you restore the cellular bands, the scanner will automatically search at the correct 30 KHz increments while in the cellular bands. The 54 to 88 MHz coverage is primarily used for TV audio in the US (channels 2 through 6), but is used for police and other services in parts of Europe.


Due to the requirements of FCC Part 15.121 subpart A, Radio Shack has modified the production of the PRO-43 and come out with a new model, the PRO-43A. This model can not be modified for cellular reception. The other two mods, 54-88 Mhz restoration, and the beep delete, are still possible on the new units.

You can determine if your PRO-43 is fully modifiable by looking at the FCC ID number on the back plate. If it reads: AA020-300, then it is modifiable. If the ID number ends with an "A" (i.e. AA020-300A) then the unit is not modifiable for cellular.  

Why delete the beep?
When you press the keys on the PRO-43, it responds with an audio beep to let you know that the key has been "accepted" by the scanner. This kind of feedback is usually desired, particularly since the keyboard of the PRO-43 doesn't provide tactile feedback. Then why kill the beep? Because the beep volume is fixed on the PRO-43 (that is, it is not set according to the volume control knob), and, at the same time, the volume is not equalized between the speaker and the headphone jack. Because of this, while the beep volume is not a problem with the speaker, when you listen to the scanner using headphones or through an amplified system like your car stereo, the beep has the effect of a concussion grenade!

The mod reduces the beep volume from the speaker to a very soft level (you have to be in a quiet room to hear it) and to the headphone jack to a comfortable level.

Some things to consider before killing the beep:

If you kill the beep, you won't get (from the speaker) the normal indication that the batteries are very low. In the case of the PRO-43, because it stores your channel frequencies in permanent EEPROM memory, you won't lose anything if your batteries go dead. All that happens is you probably won't notice for a while that the scanner is not scanning anymore.

Another positive side of killing the beep is that when you use alkaline batteries, you may have as much as three full hours of usage after the scanner thinks that the batteries are low. This mod keeps you from going batty listening to that beep for those three hours.  

You do lose, however, the feedback the scanner gives you when you enter an incorrect entry. Say you are going to program in the frequency 455.675. You enter in the 455 but don't hit the decimal point properly. If you could hear the beep, you would notice it stop beeping after pressing the second 5 (because it thinks you are entering a channel number that is outside of its range). Without the beep, you have to rely entirely on the LCD display to tell that something is wrong. Not a big deal, but there are several kinds of operations that the PRO-43 helps you with that are similar to this one.  

Performing the modifications:
You should have experience soldering and should feel comfortable working with very small parts to perform these mods.  

You will need a small Philips screwdriver, a small slotted screwdriver, small needle-nose pliers or tweezers, a low-wattage soldering iron, and a solder sucker or solder wick. A magnifying lens of some sort (eyeglasses or lamp) and a high intensity lamp are highly recommended!  

All the references to positions assume that you have placed the PRO-43 with the keyboard side down and the antenna at the top.  

1) Remove the antenna and the battery pack. Then remove the 4 black Philips screws from the back of the case. Put these and all other screws in a secure area.  

2) Pull the back case off. The case will separate near the front of the scanner, revealing the stacked circuit boards inside. Place the scanner down on its face. You will encounter three circuit boards. The top board is the one you will see looking directly down. There is a second board in the middle, and the third board is the board that has the keyboard attached to it. The top and second board are connected together and will move as a unit.  

3) Remove the six small screws from the top circuit board. Place these screws in a secure place.

Fig 1 

4) The top and middle boards are connected at the bottom left by a small black 4-pin connector. Take your small, slotted screwdriver and use it to carefully pry up the black connector at the bottom of the top circuit board. A good place to pry up the board is above the metal shield on the left, bottom edge of the board. Once you lift up the top board by freeing this connector, you can shift the top board slightly to the left and right. By shifting this top board to access the screws underneath, you will not have to desolder the antenna connections.  

First, shift the top board to the right so that the Philips screw on the lower left edge of the middle circuit board is exposed. Use your small Philips screwdriver to remove this screw. You may need to use your needle-nose pliers to grab this screw once it's loosened.  

fig. 2

5) Shift the top board to the left so that the screw at the lower right edge of the middle board is visible. Use your small Philips screwdriver to remove it. You may have to angle the screwdriver slightly to get to the screw. The needle-nose pliers may also make it easier to remove the screw. Store these screws with the others.  

6) Once both screws are removed from the middle board, the whole unit of the top and middle board will lift out and "fold" over to the left. In order to lift up, you have to disconnect two connectors along the right edge of the middle board. There is a small connector near the top right of the board and a longer one along the middle right edge. Again, use your slotted screwdriver to carefully pry these connectors loose.  

(To delete the beep)
7) After you've folded the two boards to the left, look at the bottom of the second board. In the upper half of the board, nearer to the left side, you will find a small surface mounted resistor with the number "471" on it. To defeat the beep sound, you need to remove this resistor. Heat the connectors on each side and use the sucker or wick to remove the solder. Even after you remove the solder, the resistor may still stick to the board. Try using the edge of an Xacto knife to pry it up if it sticks. Otherwise, use your tweezers to pick it up. Try not to destroy it, since you can re-install it if you want to restore the beep. Tape this chip to the back of a business card or something similar for safe keeping.  

8) Now look at the bottom circuit board. There are a set of five diodes that affect how the scanner scans. They are covered by the metal RF shield. Desolder all four tabs that hold the RF shield in place. Use your screwdriver to put a slight upward pressure on the shield near the tab you are heating and it will pop right out. Remember the orientation of the RF shield so you can put it back the same way when you re-assemble the scanner.  

9) After you remove the RF shield, locate the row of diodes. The labels are not quite lined up with the diodes themselves, so be sure you can identify which diodes are which. In a normal US PRO-43, you will see diodes 1, 2, and 4 installed. Diodes 3 and 5 are not present. These diodes are extremely small so you will have to be very delicate in handling them.  

(To restore cellular)
10) Remove the solder on each side of diode 4, using the solder wick or solder sucker. With tweezers, carefully lift diode 4 off the board. These are surface-mounted components, so the leads are not soldered into holes in the board but are attached directly to the surface of the board. If you use pliers, be extremely careful, because you may crush the diode. You will still get cellular restored, but you will not be able to place the diode in D3 to restore 54-88 MHz.  

(To enable 54-88 MHz)
11) If you were able to lift the diode off intact, place it over the pads in the space for D3. Keep its orientation the same as it was on D4. Carefully solder the diode in place.  For your information, the diode matrix performs the following functions:  Diode 1, if removed, disables the keylock switch. If in place, enables the keylock switch. Diode 2, if in place, enables the 30-54 MHz range. If removed, disables 30-54 MHz. Diode 3, if in place, enables the 54-88 MHz range. If removed, disables 54-88 MHz. Diode 4, if removed enables the cellular bands. If in place, locks out the cellular bands. Diode 5, if in place, steps the cellular bands in 12.5 KHz steps. If removed, steps in 30 KHz steps.  

12) Resolder the RF shield on, being careful to replace it in its proper orientation.  

13) Take the top and middle circuit board unit and fold it back to the right, lining up the pins for the right edge connectors.  

14) Replace the screws in the middle board, again, by shifting the top board to the left and right. You may need to seat these screws in their holes using your needle-nose pliers or tweezers.  

15) Insert the black connector at the bottom of the top board, and replace the 6 screws in the top board.  

16) Replace the back case, replace the 4 black screws, replace the battery pack and the antenna.  

To test the unit:
Enter the following key sequences:  


Now press the up arrow. The scanner should now be able to search through the cellular base range. It will use the proper 30 KHz steps.  

Now try:  


Again press the up arrow. The scanner should now search through this low band range of 54-88 MHz. It will step in increments of 5 KHz.  

If you performed the beep delete, you will notice that the beep sound is very quite through the speaker and comfortable with headphones.  

Note on TV audio frequencies:
The range of 54 to 88 MHz is primarily used for TV audio of channels 2 through 6 in the US. TV audio is broadcast on wide-band FM (WFM). The PRO-43 only receives FM in narrow band FM, which means that the quality of TV audio won't be perfect. It should, however, be very understandable, which means that you will be able to listen to the six o'clock news (for example) on some of these channels with no problem.  

TV audio frequencies:  

Channel 2 59.75 MHz
Channel 3 65.75 MHz
Channel 4 71.75 MHz
Channel 5 81.75 MHz
Channel 6 87.75 MHz  

Note on cellular restoration:
There is much controversy about the 1986 ECPA legislation which made it illegal to monitor cellular communications in the US. You should be aware that the law makes it illegal to monitor these communication, not possess a device that can monitor them. In other words, it is not against the law to modify your scanner to pick up these frequencies. It is just against the law to listen to them! Please use good judgement if you make this modification.  

Note about Radio Shack and the modifications:
I certainly cannot speak for Radio Shack, but many scanner enthusiasts have found that making modifications such as these will not necessarily void your warranty. While it might do so technically, it seems that, if the mods are not related to other problems that you have with the unit, Radio Shack may very well fix the unit under warranty and leave your mods in place!

Note however that the PRO-43 has since been discontinued as a product and the original digital boards that supported the cellular mod are gone from inventory. As Radio Shack rarely does component-level repairs, it is likely that a new, non-modifiable digital board may be swapped in during a repair. You may want to make arrangements with Radio Shack not to swap the digital board if they would ordinarily do so and try to find someone to repair your unit at the component level.  

Thanks very much to Jeff Goldman, Bob Kelty, Gary Ross, Todd Handley, R.G. Schaffrath and others who helped pioneer these mods and discover what makes the PRO-43 tick inside.  

Howard Bornstein
Design EQ
[Home Page][Radio Products][Misc Scanner Info][Radio Links]