HF Digital Messaging - Emergency / Disaster Relief - Interoperative Communications - Ham Radio
Icom IC-718 Transceiver Quiet Relay Scan Mod
About the modification
The following is a basic overview of a Quiet Relay Scan modification developed for the Icom IC-718 transceiver for use with ALE (Automatic Link Establishment). The same principles could possibly be applied to other radios having similar circuits. Also, please see the related mod, IC-718 Microphone Mute Mod for ALE.
Circuit modification theory
The +13V supply voltage to the transmit bandpass relay driver IC has been cut,
and a transistor has been inserted to control the + voltage to the IC. The base
of this transistor is connected to a point in the circuit that goes to +13V on transmit. The receive bandpass filter bank is controlled by diode switching via another driver IC and this has not been changed. Thus, the transmit bandpass relays are only activated when transmitting. They are completely inactive and silent during receive, and when scanning or changing bands.
Warning
This modification is not approved by Icom! This modification is for educational purposes only. If you decide to risk working on your radio, keep in mind that the warranty may be void when you do this. Don't even attempt this modification unless you are technically qualified to follow it through properly. If you are not technically qualified, it is suggested that you either seek out someone who is qualified to do the mod, or else don't do the mod. If you destroy your radio, it is entirely your fault. No liability is assumed by HFLINK, HFPACK, or the author. You have been warned.
Note
The receive preamp will be rendered non-functional by this modification. The IC-718 preamp famously suffers from overload anyway, so disabling it may be a blessing. The use of Full Break-In CW is not recommended with this mod because it is likely that it will add key clicks when the bandpass relays are being rapidly switched by fast morse keying. This will not cause a problem in other modes such as ALE or SSB or digital.
Tools
1. Pointed tweezers
2. Pointed tip soldering iron
3. 60/40 Lead Solder, multicore, small diameter
4. Magnifying lamp
5. Needle nose pliers
6. Diagonal cutters
Parts:
1. NPN Transistor, PN2222, (2N2222) or similar
2. Small insulated wire, such as wire-wrap
The modification procedure
1. Preparation: Remove the bottom of the IC-718 radio enclosure, and locate the area
of the Main PC Board near J4001. Pull the flex cable out of the J4001 socket, and tape it temporarily out of the way. Unplug the cable from J201 and place it out of the way.
2. While applying the soldering iron, gently lift and bend PINS 9 and 11 of IC3003 slightly up and away until they are free from connection to PCB pads. Do not bend a pin very far, or it will break off.
3. Cut the leads of the NPN transistor to approximately half of the original length.
4. Solder the collector of the NPN transistor to the non-grounded side of SMT capacitor C3002.
5. Solder the emitter of the NPN transistor to the lifted PIN 9 of IC3003.
6. Prepare a wire of the proper length and solder one end of it to the base of the NPN transistor; solder the other end of this wire to PIN 10 of J4001.
7. Prepare a wire of the proper length and solder one end of it to the solder pad that previously was connected to PIN 11 of IC3003; solder the other end of this wire to PIN 9 of IC3002. Leave the PIN 11 of IC3003 floating, it is not connected.
8. Inspect the work with magnification. Plug the cables back in that were previously unplugged. Test the radio on the bench with a dummy load transmitting, and an antenna for reception. Use the band selection and test every band for transmit power to verify that the relays are working.
9. Assemble the bottom part of the radio enclosure. Modification is complete.
©2009 HFLINK. All Rights Reserved.
PHOTO OF COMPLETED MOD (click to zoom)
PHOTO DIAGRAM OF MOD (click to zoom)
SCHEMATIC DIAGRAM OF MOD (click to zoom)
PC BOARD LAYOUT DIAGRAM OF MOD (click to zoom)
©2009 HFLINK. All Rights Reserved.
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©2009 HFLINK. All Rights Reserved.
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