Orion 900MHz Ham Radio Modification

The Orion will transmit on both 902 repeater inputs and 927 outputs in talk around or simplex mode. To get the 902 TX one must do a hardware modification to force the VCO into the proper range. It will be up to you to figure out how to program the radio onto 902 and 927MHz. I figured it out and so can you.

Once you have the radio programmed on the ham bands and working on 927MHz TX and RX but you have the VCO unlock on 902MHz TX you are ready to modify the radio. Use ESD safe work practices so you don't fry the radio you wish so badly to have work. Other than basic hand and soldering tools, you will need one item to complete this mod....A piece of small gage wire!


Hardware Modification:
1.Remove the PA and set it aside to get it out of the way.
2.Remove the top and bottom covers and internal shields.
3.If a dash mount radio, remove the control panel from the front.
4.Remove the VCO circuit board and set it aside. 
5.Remove the Logic circuit board and set it aside.
6.On the Logic side of the chassis you will see a raised boss that is the heat sink for the 7805 regulator chip. Set the chassis in front of you with the boss to the right. On the side of the boss facing you (towards the front of the radio) drill a 1/16” hole right along the boss on the front side about 1/8-3/16” of an inch from the end of the boss. This is where the VCO control wire you add will pass through the chassis.
7.Place the VCO board front and center on your bench, componet side down with the connector to the Logic board closest to you. The VCO adjusting caps should be towards the bench on your right hand side. Locate the surface mount resistor and capacitor near two plated through holes in the board. These will be towards the right edge with nothing between them and the far side of the board. They will be near one of the holed for VCO board shield mounting. The cap is marked 102 and the resistor marked 472. They share a common connection. This line is the “Synth Band 1” line from the micro. The resistor is the current limiter for the transistor this line drives. It is high for talk around VCO and low for repeater input VCO. We will be pulling this line low to make the radio lock at 902-903MHz. We can do this without damage to the micro since this resistor is in the circuit. Carefully solder a length of small, insulated wire to the right hand side of the resistor (the trace leading to the cap and the plated through hole).
8.Run the wire through the hole you drilled in the chassis and reinstall the VCO board. Do not let the wire loop up or collect under the VCO board. Gently pull it as you place the board.
9.On the Logic side of the chassis, run the wire around the 7805's heat sink boss and out the cutout in the chassis for the PA connections. Reinstall the Logic board, keeping this wire out of trouble under the circuit board.
10.With the Logic board side up, and the front of the chassis towards you, locate TR716 on the Logic board, near the back of the radio. There are two identical transistors one above the other. This one is the one farthest back. They have 3 leads on the right side, and one larger one on the left. Bring your wire up and around the back of the board and solder it to the center pin on the right side. This is output 1 that you will use to control the VCO. 
11.Locate J703 and consider cutting the traces that lead to pins 3 and 4. This output 1 appears on pin 22 on the 37 pin connector. By cutting the traces, you ensure that nothing will be connected and damage the modified circuit.
12.Reinstall the shields and covers. Reinstall the PA deck.

This completes the hardware modification.

Radio programming (No, not out of band. You already did that on your own):

1.Under “Control Unit Keypads” select the control unit your radio has an assign one button to “MAC1” (macro 1). You will use a macro to select talkaround and toggle the VCO.
2.Under “Macro Keys” select “macro 1” and “press”. In the box next to the number one select “Talk” and “Press & Release”. This selects the talk around mode. In the box next to the number two select “AUX1” and “Press & Release”. This will toggle the output line we use to control the VCO.
3.Under “External IO” in the area that relates to AUX 1 select “Follow WHC Icon”, Aux 1 output = 1, Aux 1 active = high, and finally check the aux 1 repeat box.
4.Program the radio with this information
This completes the radio programming for the VCO control.

Now when you press the key you assigned to macro 1 you will hear two beeps. The first one is the radio going into talkaround, the second is the output changing state. Press it again to go back to repeater mode and ground the VCO control line we added.

See how easy. Not bad for a couple hours of work.

73 de K6ZRX