Modifications for the ICOM - RogerK

●●●●●●●●●●remove the capacitor (C61) fitted in place of FI3solder in FI3readjust R72 for proper IF gaincut wire PBTV (pin 4, P1/J1, MAIN, yellow) about 5cm from the plug (P1)cut wire AMO2 (pin 3, P2/J18, MAIN, red) close to the plug (P2)cut wire AMO3 (pin 4, P2/J18, MAIN, metal baird) close to the plug (P2)connect PBTV wire (the end not connected to the plug) with AMO2 wire (the end not connected to the plug)connect AMO3 (the end not connected to the plug) to +8V e.g. by tapping (pin 1, J4, MAIN, brown).connect the wire stubs on the plug (AMO2 & AMO3) together is you wish to use external modulation input for PACKET etc.adjust the coil next to X2 (PBT VXO) for correct middle PBT settingThis modification is read 707 times.top of page27-10-1998(IC-275) Modification of cw pass band (BFO)Problem:In these transceivers ICOM has chosen to shift the CW passband up 200 Hz compared to the SSB passband. This makes it moredifficult to copy SSB signals in CW mode.Solution:The extra BFO coil that is added in CW-R is short-circuited, and the BFO is re-adjusted for proper CW RX/TX-tracking and forpreferred USB/CW passband.Implementation:●short-circuit Lcw in the BFO compartment.For readjusting the BFO you need another transceiver (TRX2) with correct tracking.1. Receive on TRX2 and transmit in CW. Adjust the VFO (with the RIT off !) of TRX2 until you have the desired side tone in CWmode. (e.g. 800 Hz - can be found by beating the tone with the side tone oscillator).2. Transmit on TRX2 and adjust Ly (CW-R) until you have the desired side tone in CW mode. (you are setting the ~800Hzdifference between CW-R & CW-T).3. Adjust Lx (CW-T) for preferred USB/CW receive passband.You might have to repeat the tuning once again, as there is some interaction between the adjustments (diode switching for highimpedance RF circuits are not perfect !). If you would like to adjust the LSB passband, this should be done by adjusting thecapacitor C, before adjusting the coils.Note: The BFO coils are switched in successively to give the required offset from the LSB frequency. Therefore adjusting CW-Talso changes USB/CW-R.