Modifications for the ICOM - RogerK

18-06-2000(IC-729) Using two Icom rigs in transceiveAuthor: Richard Mekka - richard@mekka.freeserve.co.uk.MODIFICATION.NETI have an IC729 and a R72 rx in the shack here, and I wanted to try some experiments with using separate aerials for receive &transmit. Getting the two pieces of equipment to "talk" to each other using the CI-V interface was no problem, but try as I mightI could not see a way to prevent a master-master situation i.e. turning either tuning knob caused the other rig to follow.What I wanted was a master-slave set-up; in my case the IC729 to control the R72 but NOT the opposite. This would mean thathaving started a QSO I could use the receiver for split operation, or as a kind of RIT.Initial thoughts consisted of having a switch to break the CI-V line as and when transceive was not needed, but this wasn't veryelegant and would involve lots of switching on and off. Then I had a great idea. What common electronic device lets signals passone way but not the other? Correct! The good old humble diode!A quick lashup proved that my theory was right. The 0.7 volt drop does not effect operation of the data signal in the desireddirection, which is a little surprising as the signal is only a 2 volt signal (unterminated) to begin with. Maybe the fanout isreduced with the diode fitted, but I have been unable to test this.In the end I made up a lead with the diode in series with the coax "inner", inside one of the jack plug covers Don't bother tryingto work out which way round to solder it: if control is the wrong way reverse the lead. It's probably worth marking the lead sothat it isn't used for audio work - might cause a few strange effects!This modification is read 542 times.top of page20-10-2001(IC-729) Modification Icom IC-729: General coverage TXOpen up the radio and locate the pll board, cut diode D5. The board should be located on the left hand side at the rear. Reset thecpu by pressing function and the mw button together while turning the radio off and on again.That will give you tx coverage from 1.6 to 30MHz!This modification is read 661 times.top of page05-10-1998(IC-730) Preventative Maintenance for the ICOM IC-730Though the IC-730 is a good-performing, reliable radio, many of these units have been in service for a number years and arebeginning to show their age. The following preventative maintenance procedures should be done to all IC-730's that come in forrepair. You will find that when you take a few minutes to attend these minor details while the radio is on your bench, your returnrepairrate for the IC-730 will be almost nil.1. On the RF unit, resolder the connectors at J2 and J3 on the RF unit. Due to the relatively thick coax cables on theconnectors, these joints tend to crack with age and cause intermittent transmit and receive problems.2. Make sure the receiver preamp works. If inoperative, replace relay RL1 on the RF unit. Install the factory update to preventrelay failure3. Check transistor Q5 on the RF unit. If it is a 2SC945Q, replace it with the improved 2SC2878B to prevent spurious outputfrom the transmitter and failure of the driver transistors. If Q5 is a type 1636, it doesn't need to be replaced.4. Clean the RIT pot and switch with tuner cleaner. These controls are usually noisy and erratic, making the RIT hard to use.5. Tighten the chrome-plated PC board mounting screws. The type of screw and spacer used in the IC-730 tends to comeloose if the radio is used in a high-vibration, mobile environment. Don't forget to tighten the screws on the logic and IFunits located beneath the main unit.6. Check the bandwidth coupler for proper tightness. Tighten as needed.