Ok, I had a look at what I did and would like to give the solution to you guys. There are some pictures which I took, which I would like to send – although I probably can’t put them on the forum. So if you need them, let me know where to send them. (You may manage ok without them) The other thing is that I will make reference to the IC-M800 service manual (NOT the user manual) which I found on the net at:
http://www.mods.dk/manual.php?brand=icom it is a zipped file.
Obviously the usual philosophical ramblings apply about due care etc. to you and your radio.
You will need:
A small Phillips screwdriver.
Small wire cutter
Solder + fine tipped iron
A utility knife
The service manual
A cable to connect the two units together for this mod. Any small type electrical cable is fine. It needs three cores. Perhaps something like signal cable normally used to wire home alarm systems could be used. Although I didn’t do this, perhaps a cable with a screen would be a good idea. (With the screen grounded).
Now for the modification:
First take the remote unit and place it face down with the rear facing you. You can unplug the power connector if it is still plugged in.
Now remove the 6 long screws that hold the two halves of this unit’s cover together.
Gently separate the halves of the cover.
If you look inside the bottom cover, you will see the fibre optic jack unit (the unit on a small circuit board that is connected to the external connector which takes one end of that fibre optic cable.)
You can see it in PIC1.jpg – (Ignore that thick black cable which is the cable to be fitted.) In this pic the two halves are lying open next to each other. My finger is above the jack unit.
Now you need to remove the jack unit. To do this, look on the outside of the bottom half at the connector which takes one end of the optic cable – (it says ‘RF UNIT’ next to it)
Remove the two screws which hold the metal plate. This will reveal two more screws. See PIC3.jpg Here the metal plate is held hovering above the connector and you can see the two more screws to remove.
Now remove these two screws and the jack unit circuit board will be released from the casing.
Now look at PIC4.jpg. Here I am holding the jack unit.
Look also on page 6 – 1 of the service manual. See under the heading Jack Units - There is the picture of the circuit board.
Note the connector J15.
Cut the red wire which goes to pin 2 of J15. (This wire is marked ‘FOR’ on the schematic which stands for Fibre Optic Rx)
In PIC4.jpg, You can see the tail of this red wire which has been cut. Ignore this wire (you could put some tape over the end)
Now take your 3 core wire to be used in place of the original fibre optic cable. You will probably need to make an entrance hole for this wire in the back of the remote unit casing. Perhaps do it at this stage and thread the wire through to observe how you will route it to the jack unit board.
In my case I used a three core household wire with these colours:
Grey – let’s call this wire 1
Orange – let’s call this wire 2
Green – let’s call this wire 3
Look at PIC5.jpg
Here I have connected green (wire 3) to pin 4 of J15 (this is shown as ‘FOT’ on the schematic which stands for Fibre Optic Tx).
So now, carefully solder this connection (wire 3) onto pin 4 of J15 – careful not to short to the adjacent copper.
Next take grey (wire 1) and connect it to ground which is the largest copper area of the board. See PIC5.jpg, Here I connected it to the negative of C92 (see the service manual layout picture again to find C92)
In PIC5.jpg you can see it just before it goes into that white gunk (actually epoxy glue) on the right hand side. You can see the grey wire coming out further on the right hand side.
You are done with the connections to the jack unit board. I put some two-part epoxy glue to ensure that the wire s wouldn’t wear loose over time. You may have a neater idea.
Now take the other end of that red wire that you cut in the beginning, it will be going to the large circuit board of the remote unit. Connect it to the third wire of your 3 core lead. (In my case it is the orange wire – wire 2). In PIC5.jpg it is connected and covered with some shrink sleeving. The orange wire disappears into some insulation tape (I think I taped it for some reason) and the thick black wire snakes out of a hole in the bottom of the casing.
If you haven’t done so, thread your wire out of the hole which you forced yourself to make in the remote unit casing.
So now you are done with the remote unit. Perhaps leave things open until all is working. We still have to do the connections to the main unit.
So now we need to open the main unit. Turn it upside down (the fibre optic connector should be near the top) and remove the 6 screws which hold the bottom half of the main unit casing. The casing is in two un-equal halves. The smaller half is now uppermost and you need to remove this one. (don’t need to remove the feet) You should see something similar to PIC6.jpg The board which you will wire to is called the connect unit in the service manual under the heading 6-2 TRANSCEIVER (1) (on page 33 of 91 of the pdf document)
The connect unit board in PIC6.jpg is the small one whose solder side is uppermost in the picture.
See PIC7.jpg for a slightly blurred close-up of it. Locate J1 in that picture of the connect unit in the service manual. Now find J1 on the actual board – NOTE that the actual board is upside-down and the service manual picture shows the top view (component side).
Now you need to possibly make another hole in the bottom casing to feed in the other end of the 3 core wire.
You need to connect wire 1 (grey) of the 3 core wire to J1 pin 1
You need to connect wire 2 (orange) of the 3 core wire to J1 pin 2
See PIC7.jpg
Now for the green wire (wire 3) – Look at the service manual picture of the board. Look at the optical connector (in front of it says ‘Remote Controller’). The connector is labelled IC3 (it is actually part of an integrated optical transceiver). Viewing this picture, note that D2 and R5 go to this connector and that they are all connected together via a more-or-less triangular shaped copper area.
(If need be I’ll scan and annotate a picture from the service manual). In fact they connect to the second from right hand pin of IC3 as viewed on the picture in the manual.
What you need to do is to locate this pin on the actual board – perhaps this is easier, and then identify the triangular shape copper bit. (Remember to think upside-down between the picture and the actual board.
Now what you need to do is to cut with a utility knife, part of this triangular copper area so as to isolate the pin of IC3.
Now connect wire 3 (the green wire in PIC7.jpg) to D2/R5 by soldering onto the copper. The isolated pin of IC3 should be going nowhere.
Now you should be up and running. Ensure all is ok and then power up both units for a test.
See how that goes – you can contact me for any un-clarities in my explanation
73
Russell – ZS1RUS