Modifications for the ICOM - RogerK

R2 . .> D1 D2> -----------+ .. ..> | -D3-> | -D4-> IC4 | -D5-> -----------+ -D6-> -D7- . .. _ _> D8 D9 _ _> O .. .> C7> X1 |> ________________________________________________________|As far as the following two, I got the impression that the IC-229H did as well at aviation band receive as my IC-2SAT.... Onethought -- since the "CQ" review described as slightly different physical construction, I wonder if there have been some slightchanges during the production run leading to improvements in AM demod performance??This modification is read 1101 times.top of page19-07-1998(IC-229) IC-229H & 9600 bauds (Anglais)After trying to solve this the easy way with no luck, by looking for docs already posted, a few of us have decided to bug this out.A quick call to ICOM put us on the rite track. This non-destructive mod for the IC229h works well for 9600 baud packet. You willneed your schematic that came with your radio. However, our call to ICOM revealed some discrepancies on the schematic in theFM detector stage, primarily the FM detector chip itself.Earlier models had the TOKO TK10487M detector and the newer models have the MOTOROLA MC3372M. ICOM, unfortunately,did not make this change in the schematic supplied with the radio. This document will show the connection points for both chips.Remember to use good quality shielded cable like RG-174u, RG-178u or similar. Most of the points are going to require microsurgery,so get out your pencil point soldering irons and magnifying glasses.1. TXA:On the schematic you will see a block labeled "VCO UNIT". At the bottom of this there is a four pin connector. The third pinis labeled "MOD".This is where you want to inject the TXA from the modem. The "VCO UNIT" in the radio is shielded by a can. Removing this"CAN" to get to the circuits can be a tedious endeavor. So you can find this "MOD" point on the underside of the radio. It islocated beneath a flat metal shield about 1" X 2". After removing this, with the front of the radio towards you, the point canbe found in the right corner towards the front where the shield covered. There will be four solder lands rite in a row fromleft to right. Trace these lands with the schematic to find the "MOD" land. Solder your TXA there. Replace the metal shield.This is as tuff as it gets. I promise!2. RXA:Well this one is easier. If your radio has the TK10487M, solder RXA to pin 11 of this chip. If your radio has the MC3372M,solder RXA to pin 9 of this chip. Either chip can be found on a board in front of the "metal VFO shield can", on the top sideof the radio. You may have to tilt the board a little, but be careful. Don't apply too much heat to the chip or you will have abig problem. I followed the trace away from the chip and attached RXA.3. PTT:This can be found on the mike jack pin 5. I made this an internal connection for neatness. Neatness counts!4. GND:If I need to tell you where to find ground, you shouldn't be doing this mod yourself. Attach all the shields from the abovewires together outside of the radio to modem ground. Attach only one shield internal to the radio, the "CAN" is a good spot.You don't want to cause any ground loops, do you? Protect the other two shields from shorting to anything in the radio.This is why they make heat shrink tubing.You may have to add 5-10mF non-polarized capacitors in series with the TXA and RXA lines. Some modems have included thesein their circuit, so check. Now you are ready to make the connections to the modem. This will have to be left up to you. Thereare too many modems and tnc's out there to list all of the connections to them. But you should have the docs with your modem,so it should be easy. Disconnect the radio from the modem if you use the radio for anything else. Well there you have it. Thisworks great, it is what I am presently using.This modification is read 859 times.top of page