Modify your ICOM R7000 to scan and search faster		
 	Author: Bob Parnass, AJ9S	
	

This article describes how to increase the scan and search speeds of the ICOM R7000 receiver by 60% without noticeable performance degradation.

Background

The front panel SCAN SPEED control on the R7000 receiver allows the user to adjust the speed of scan- ning and searching operations, as well as the rate at which the priority channel is sampled. Rotating the control counterclockwise decreases the speed, and rota- ting it clockwise increases the speed.
When the SCAN SPEED control on my R7000 (serial number 001400) was turned fully clockwise, the radio would scan a maximum of about 8 channels/second, or search about 8 increments/second. As the following table shows, the stock R7000 can scan about as fast as a Radio Shack PRO-30 or PRO-2003.
TABLE 1. Maximum Scan Rates of Selected Receivers

      _____________________________________________________
     |             Scanner               Maximum Scan Rate|
     |                                |  (channels/second)|
     |________________________________|___________________|
     | Kenwood TR-2600                |         1.2       |
     | Radio Shack PRO-30             |         8         |
     | Radio Shack PRO-2003           |         8         |
     | ICOM R7000 (stock)             |         8         |
     | ICOM R7000 (after modification)|        13         |
     | Regency M400                   |        13         |
     | Bearcat 20/20                  |        15         |
     | Bearcat 300                    |        15         |
     |________________________________|___________________|
R7000 Scan Circuits

The scan rate of the R7000 is determined, in part, by a simple clock outside the microprocessor. The front panel SCAN SPEED rheostat and resistor R18 (and other components in the LOGIC UNIT) control the speed of this clock. The clock output is connected to what appears to be an input port on the microprocessor. The upshot is that we can affect the scan rate without affecting the other chores performed by the microprocessor.
The modification consists simply of soldering a 470,000 ohm resistor across the leads of resistor R18 on the LOGIC UNIT circuit board.
How was the value of 470,000 ohms chosen? Experimenta- tion with different resistor values showed that for values both above and below 470,000 ohms, the R7000 scan rate decreases. Not having the R7000 Service Manual, I assume this can be explained by the firmware within the microprocessor associated with the scan rate input port.2
Adding the 470,000 ohm resistor in parallel with R18, rather than just replacing R18, has a few advantages:
The modification is easily undone, returning the radio to stock condition. 
The LOGIC UNIT board does not have to be removed, as would be the case if R18 was unsoldered from the foil side. 
Making the Modification

Accessing this circuit board is not difficult, and involves the same steps used when installing the optional Remote Controller or Speech units.
Use a towel to cover your work area to avoid scratching the R7000 cabinet. Unplug the R7000 from the AC line, and turn the radio upside down. Remove the bottom cover by removing the 12 screws holding it in place. Remove the 4 screws holding what ICOM terms the "parti- tion panel". Pictures on pages 32 and 34 of the R7000 Instruction Manual show the partition panel. After removing this panel, the component side of the LOGIC UNIT circuit board is accessible.
Perhaps the firmware polls the scan rate input port infrequently. Another possibility is that the scanning pulses interrupt the processor, and the interrupt firmware is limited in its ability to process frequent interrupts.
Locate R18, a 270,000 ohm 1/8 watt resistor, near con- nector J5. You may wish to remove plug P5 from J5 tem- porarily if it gets in your way. Carefully solder a 470,000 ohm resistor in parallel with R18. I used a 1/4 watt resistor as it was the smallest on hand.
Reassemble the radio, connect it to AC power and antenna, and enjoy.
In the modified R7000, the scan and search rates are still adjustable using the SCAN SPEED control. With the control turned fully clockwise (maximum speed), the modified R7000 scans at about 13 channels/second and won't miss weak signals.