Magnum 357DX Conversions

As mentioned in this month's review of the Magnum 357DX, there are different conversions that can be performed on this radio. Two will be covered in this article. Remember to always disconnect electronic equipment from the power source before doing any modifications. The most common and simplest conversion is cutting the diode lead on the front panel CPU PC board. You can see the diode location in the photo below. After the diode is cut and before the power is applied to the radio, short out the two Reset Pads illustrated in the photo below. The conversion is now complete. Every time the radio is turned on, the radio comes up in the 10-Meter only band. All the functions operate as described in the Operating Manual. To toggle to 10 & 11-Meter operation, momentarily press the CLAR/FUNC control, then hold the CALL button for 3 seconds and release. This will be required each time the radio is powered on until an 11-Meter frequency is programmed into memory. If an 11-Meter frequency is in memory, simply load it in as described in the Magnum 357DX review or Operating Manual. The diode conversion retains the three position STEP command in the 10-Meter only band. Each time the step button is pressed, one of the digits on the LCD frequency display right of the decimal point flashes. Either the UP/DOWN buttons on the microphone or the frequency selector on the front panel will change the digit from 0-9. Only that digit will change under this command. The next digit to the left will remain unchanged while in this mode. The operator can select and change the 1KHz, 10KHz, or the 100KHz digit while it is flashing. To exit the STEP command simply press the step button until there are no flashing digits or momentarily press the microphone PTT switch. The second conversion is the full coverage conversion. The down side to this conversion is that the radio can't be toggled back to the 10-Meter only operation and none of the commands associated with this operation can be accessed. The up side is the radio powers on with the last frequency used without the addition steps required in the first conversion. You must decide which is best for your needs. To perform the full coverage conversion a resistor must be added to the circuit traces shown in the photo below. The diode need not be cut, but if it is already, it won't have any effect on this conversion. The spacing of the pads are for a SMT 1/10 watt resistor. The value required for this conversion is 47KOhms. Good soldering skills are needed to perform this modification. The pads are delicate and will lift off the board with excessive heat. A low wattage small tipped iron is essential. If you choose to use a standard resistor, a 47K 1/8 Watt is preferred for it's small size, but a 1/4 Watt is OK. It's recommended that the circuit traces be followed to other components already attached to them and the standard resistor be soldered to them at those points for added strength. Mounting a standard resistor to the pads meant for the SMD part means the resistor will have to be mounted vertically and the additional stress in mobile operation could and most likely would damage these circuit traces over time with the vibration of the moving vehicle. After the resistor is added and before the power is applied to the radio, short out the two Reset Pads illustrated in the photo below. The conversion is now complete. Bob F

Magnum 357 DX Front Panel Printed Circuit Board

January 2002 Web Edition