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MAYCOM EM-27
Maycom EM 27
This describes how to add more channels to the Maycom EM 27
Converting the Maycom EM 27 UK 80 Channel Version to the 400 Channel version,
and additional channel programming information
There are two methodes, the first method I found at http://www.c-and-l.freeserve.co.uk/ this is a site that is well worth a visit if you want to buy CB related parts in the UK, and is also the basis of the second method that I created, the first method will cause the radio to always turn on in the 80 channel mode, the second will always be in the 400 channel mode (it has not been tested yet, if you try it and it works, let me know).
Method 1
Fix a 12v double pole changeover relay to the PCB with double sided tape.
Remove the 0 ohm resistor link from pad 2.
Wire up as shown in the diagram.
Solder a diode across the relay coil and leave the legs long enough to wire to the radio.
The cathode is soldered to the cathode of the diode on the PCB as shown.
Anode goes to a suitable ground point.
At switch on, the radio will be in 80 ch mode.
Press M1 and M5 and it will reset to 400 ch mode.
Check that it transmits over the full range.
Adjust the two coils shown if required.
Method 2
This is a simpler mod to do as you do not need to install the relay.
Just remove the jumper resistor (it is a zero Ohm chip) from pad number 2 and put it on pad number 7.
The radio will now be in 400 channel mode.
You may need to tune the coils pictured above to get full coverage.
Bonus Info !
The picture below is a programming diagram that shows the chip positions for all of the programming modes !
bmzalewski