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 Magnum 257 Radio Modification


This modification applies to the Titan II RPSY-485
as well as the Magnum 257, 357, 457, and the 
Superstar 4900 Mobile, and Pro-Star 400 Mobile.
Disclaimer: This is for informational purposes only. All 10 meter and export CB radio mods, adjustments, tune-ups, channel/frequency expansions, modulation, power adjustments are related modifications are done at your own risk!

To have either 10 meter only or expanded operation.

  1. Hook up radio to power and turn on for a minimum of 10 seconds.
  2. Turn off radio and disconnect from all power sources.
  3. Remove Botom cabinet cover.
  4. Remove (unsolder) Diode D2. This is the only Non-Surface mount component found in this area.
  5. Reset the radio CPU by temporarily shorting the two front panel circuit board pads located near Just Right of Black Potentiometer.
  6. Hook the radio back up to power and turn on the radio.
  7. Press the FUNC button, then press and hold the CALL button for approx. 3 seconds. The band indicator will appear on LCD.
  8. Use the CALL button to select bands.
  9. To switch between channel and frequency display, press the FUNC button and press the CALL button.
  10. When turned off and on again, the radio will always default to original 10 meter settings. To automatically return to last used frequency and mode, press the FUNC button and then press and hold the CALL button for approx. 3 seconds.

Microphone configuration

Pin     Description
1       Audio
2       Receive
3       Transmit
4       Ground = Channel Down, 2.2K ohm to Pin 3 = Channel UP
5       Ground and Switch common
6       13.8 Volts. Watch it, this is not current limited.

RV-1    S-Meter Signal Strength
RV-4    AMC, AM Modulation
RV-8    RF Output Meter
RV-9    ALC, SSB Modulation and Peak Power.
RV-14   FM Carrier Power
RV-16   AM Carrier