I searched all over the net looking for info on these radios, and never really found an all-in-one place that had everything that I needed.  One resource that was very helpful was the EFJohnson Yahoo group.  There you can find some diagrams, the actual RSS and other hints and tips as well as the actual radio manuals, which were just recently posted in Feb of 07, but there still weren't any pictures to speak of, which I find very helpful.  So.....  As I am sure there are a gazillion of these radios out there, I'm going to attempt to document some of my findings here.

These mods are going to be based on the 7184 UHF 8-Channel radios, and as I found when going through the stack of radios that were given to me, there was a 7186 in the mix, so there will be some stuff on those as well.

Bottom view of a UHF 7184.  Remove the two screws on the bottom cover, the two concentric knobs on the front panel (Vol/Squ) and slide the case forward to remove it.

Solder side of the Audio/Logic board.  The radio is actually sitting right-side-up in this photo.  

While I was taking all the radios apart to clean them up, I got to about the 4th one, slid the case off, and said to myself, Hey, this one's a little different.  New version?  Nope, different model.  This one's a 99 channel!!

Okay, back to the 7184....  Front of radio.  Channel indicator on the upper left, stack of 4 LED's beside that.

Top GREEN = Busy, RED = Transmit, YELLOW = Message (when the correct CTCSS tone has been received, this LED comes on until the mic is taken off hook and returned, and the bottom GREEN = Monitor/Carrier Squelch.

Radio separated.  Remove 5 screws from the audio/logic board, flop it over and rest it on the two pegs along the edge of the chassis.  Put a couple screws back in to hold that in place, and the radio will be very easy to work on.  (The pegs and where to put the screws will become obvious once you open the radio up.)

Upper half is the Audio/Logic board, bottom half is the RF board.  Receiver front-end tuning are the 5 helicals just to the right of the synthesizer (directly behind the speaker) 

Closer view of the front-end tuning, and synthesizer shield.

Audio/Logic component side.  Most connections for repeater and link use can be found on the ribbon cable, however, COR needs to come from the busy light and TOR comes from Pin 13 of U402, located to the right of the ribbon cable.

The TTL programming connections for the edge connector are:  (Also, see below for further info on programming)

As you look at the picture of the component side of the Audio/Logic board above, with the edge connector on the right, the pin next to the notch in the PC board is PIN 1, working toward the antenna connector, are pins 3, 5, 7 & 9.  Notice Pins 7&9 are physically jumped together at ground potential.

Pin 3 = RX Data

On the solder side of the board, are the even pins.  The pin closest to the notch in the PC board is PIN 2, then working toward the antenna connector are pins 4, 6, 8 & 10.

Pin 8 = TX Data

As I didn't have an edge card connector for my home made RIB, I just soldered my TTL lines directly to the radios while I was programming them.  This turned out to work just fine.

J403 --- The Ribbon Cable -- Pin 1 is closest to the LED display

Pin ---- Description

1 - Filtered RX audio
2 - Channel Step Sw
3 - Mic Audio
4 - PTT
5 - Hanger
6 - Adaptive Filter
7 - Data
8 - Clock
9 - Enable
10 - Lock Detect
11 - TX Audio
12 - T/R select
13 - RX Detector Audio
14 - Squelch Noise
15 - 9V
16 - CPTT
17 - TOT Audio
18 - Ground

COR can be found on the solder pad closest to the front edge of the radio under the 4 LED stack on the audio/logic board.

And I've discovered by poking around, that TOR (CTCSS logic) can be located on Pin 13 of U402.  Ground the Mic hang-up button, or better yet, ground Pin 5 of J403 and your receiver will be full-time tone squelch.  Also you don't need the mic plugged in at all now.

I probably should mention that after I interfaced a repeater controller to the radio for COR and TOR, the controller loaded down the radio and things didn't work quite as planned.  So, all that was required was the addition of a couple Mosfets to buffer the radio and now it plays just fine.  Use a couple IFR510 Power Mosfets - Radio Shack P/N 276-2072 or equiv.  Ground the Source lead, connect the Gate to the radio logic points and then, run the Drain to the controller.  Easy, dirt cheap and works flawlessly!

I've also had a few inquiries about the pin-outs of the front panel Mic Jack, so...

J103 - Pin-outs:

Close up of the synthesizer shield.  See that BLUE pot standing on end by the helicals?  That's R163, the TX Power output adjustment.  

Cover removed from the synthesizer.  That silver IC looking thing along the bottom edge is where you may need to either remove or add jumpers to adjust the VCO control voltage.

If you need to re-program your radio, you're going to need the RSS, and a TTL/RS232 converter to put between the radio and your DOS computer.  No windows stuff allowed here.  Run the RP7175.exe application.

I ended up building a Radio Interface Box out of parts obtained from Mouser Electronics from the schematic below.  This diagram came from the Yahoo Group, and as you can see, it's pretty simple.  About 3 bucks worth of stuff and a little solder and you're good to go.

It aint pretty, but there it is...  The homebrew RIB...  And it works just fine!!!!  Also, I found out that this RIB works on Kenwood TK-862G's.  As you look at the front panel of the TK, Pin 1 of the mic jack is on the right and pin 8 is on the left.  The data lines are Pins 4 & 7.

Make sure when you put on the DB9 for the computer connection, that you jump pins 4 & 6, and also jump pins 7 & 8 to take care of any hand-shaking issues.

Schematic of the MAX232 Chip.

RS232 Pin Assignments

CTCSS / PL / CG Tone List

7186 laid open.  Notice there are now two LED channel segments and all the service mount stuff, but otherwise, it's pretty much identical.  Quickly looking, I only saw two immediate differences on the RF board.  The squelch pot for the remote head is present, and there's an ICOM just above the synthesizer shield.

7186 Audio/Logic board.