Date: Thu 9 Feb 89 12:02:25-PST From: Brad Horak Subject: Icom IC-900 mods To: MBramwel@business.uwo.ca Enclosed is a list of frequency range extension modifications for the IC-900. They are courtesy of KB1MZ and KA1OKQ. Some mods may enable out-of-band transmission. Transmitting there is ILLEGAL ! These radios are not type accepted so therefore it is ILLEGAL to use this radio out of the ham bands even if you have a license to do so. (ie volunteer F.D. etc). All mods are done at your own risk. This is in NO way an invatation to break the law. The mods are provided for information only..........................73 Gene WA1UXA #Subject: Icom IC900 mods Frequency Expansion Modifications for the ICOM IC-900 All changes are made in the control head. Diodes are arranged in a 8x4 array: A-H, 1-4. As shipped from the factory, the diodes are arranged thusly: X = diode in place ____________________________________ | | X | X | | | | | X | 4 |---|---|---|---|---|---|---|---|--- | | X | | X | | | | | 3 |---|---|---|---|---|---|---|---|--- | | X | | | | X | | X | 2 |---|---|---|---|---|---|---|---|--- | | | | | | | | X | 1 |---|---|---|---|---|---|---|---|--- | A | B | C | D | E | F | G | H | To add recieve coverage on 6 meter and 70 cm bands only: C=cut diode, or remove ____________________________________ | | C | X | | | | | X | 4 |---|---|---|---|---|---|---|---|--- | | X | | C | | | | | 3 |---|---|---|---|---|---|---|---|--- | | X | | | | X | | X | 2 |---|---|---|---|---|---|---|---|--- | | | | | | | | X | 1 |---|---|---|---|---|---|---|---|--- | A | B | C | D | E | F | G | H | 440 Band - to expand coverage from 420 - 470 MHz: Remove diode D25 (3,D) for RX Install diode in (3,C) for TX VCO in 440 module covers a 20 MHz range - re adjust as needed. 220 Band - to expand TX coverage from 216 - 236 MHz: * This mod hasn't been tried and verified. * Install diode (1,C) for TX Remove diode (2,D) - ? 144 MHz Band - to expand TX coverage from 138 - 174 MHz: Install diode in (1,C) 50 MHz Band - to expand coverage from 40 - 54 MHz: Remove diode D32 (4,B) for RX Install diode in (4,A) for TX 28 MHz Band - to expand coverage from 28 - 40 MHz: Remove diode D32 (3,B) for RX Install diode in (3,A) for TX ------------------------------------------------------------ ICOM IC-900 Memory Expansion Modification (Preliminary Rev II) This modification, done to the controller head, will double the amout of available memories to two banks of ten memories per band. Remove the screw from the back of the control head, and carefully open the unit. Remove the five screws holding the "Display B" unit buard to the rear cover, and unplug the white three pin connector that goes to the "beeper". Locate IC2, the 24 pin RAM chip on the back of the board. Carefully cut the small etch between pins 19 and 20. Solder a #30 wire about 6 inches long to pin 19, (address bit 10). Solder a 22K 1/4 resistor to the cathode of D5, (1N4002). This is a good "pullup" voltage. Locate this resistor next to D5, on the top side of the board. Connect the wire from pin 19 of IC2, and another 3 inch long #30 wire to the other end of the 22K resistor. (Trim the wires as needed). The "DIM" switch is connected to two fine etches that go between diode D5 (1N4002)and the rectangular cutout on the board. Carefully cut these two etches, removing at least a 1/16 inch section of each etch. Carefully scrape about 1/16 inch of the green varnish on the "upstream" side of these two etches (one of them is connected directly to the cathode of D5. Bridge these two etches together. (The display will now be only "bright", but this is no real loss, since the display isn't all that bright anyway). On the bottom side of the board, there are three pads for the "DIM" switch, with two of them connected together. There will be a glass zener diode (D2) across this switch. Remove this diode. Solder a short piece of wire from these two pads to a convenient ground point on the board. Solder the 3 inch piece of wire from the 22 K resistor to the third pad of the DIM switch. When the DIM switch is in the "bright" position (down) the memory will contain the original data. If the switch is in the "dim" position (up), then the second bank of memories can be loaded and used. Combined with the RX and TX expansion mods, this is a good way to have the first bank loaded with ham band freqs, and the second bank filled with police/fire/whatever channels. The new bank of memories will read 999.9995 MHz when first called up, and will have to be loaded with the desired frequencies, offsets and PL tones. (This is not a way to open up the RX to receive the 800 - 950 MHz band, unfortunately). Ed Brown KB1MZ Copied from the QRZ! Windows Ham Radio CDROM