I made these repairs in September of 2013, but a post this morning from another ham with the same problem prompted me to dig up the info and post to hopefully help others with the same problem.
My Icom 756 (not pro model) lost it's CI-V port from energy induced into the CI-V cable during a near lightning strike. I've read where folks have found the problem to be the transistor pair q801 & q802. This is a buffer circuit on the CI-V port input on the rig, prior to the processor. I found them on the schematic and ordered those in. VERY cheap, only a couple of bucks. My problem was, I couldn't physically find them on the main unit board. All of the pdf's I found online are far too blurry to see the part...
I was referred to Scott Malcom at MTS. He was a tremendous source of help, and sent me a couple of pics of the main poard with the parts I was looking for, circled for my ease of location. Super nice guy, really knows these rigs, I'd recommend him for service if you need to send your rig somewhere for repairs.
I replaced q801 & q802. I tested all of the smd resistors in the circuit and found them to all be OK. Once I got the CI-V port transmitting data (nice TTL level data seen on a scope), I tried every possible combination of baud rate setting on the USB port, the rig, and the software...but nothing worked. I verified the rig address (50H), and everything was OK. Really had me scratching my head...I pulled the rig apart 4 times while testing voltages and ruling out problems, bit by bit.
I used a little breakout board and level converter I borrowed from a local ham friend, and went directly from the DB9 com1 port on the computer and could get things to talk. I had installed the drivers associated with the USB CI-V replacement cable I got from Kawamall (same folks the previous cable came from), but it would not talk, no matter what. I got an email from Clint W5CPT that directed me to this link for drivers:
I found, running winXP, the drivers sent from Kawamall with the level adapter cable were a version that was not compatible. I downloaded ver 18.104.22.168 from the link Clint sent over, installed them, and all is now well.
Thanks for the help and feedback from everyone, especially Scott Malcom for assistance locating the transistors on the main PCB and answering several questions and giving his opinion, it helped me work my way through this process and get my rig up and running again.
I've uploaded the bits that might help someone else with a blown CI-V port like I have, and you can find them at:
By the way, I use the ribless programming cable from Kawamall on eBay for my CI-V interface, instead of the Icom CT-17. It works on most all Icom rigs and only costs only about $20.Lastly, I'd recommend, when you disconnect your antennas for protection from an electrical storm. also unplug the CI-V cable from the rig :-)