Hardware Hacking

Cobra 150 GTL CB Channel Modification

One of the easiest mods to do.  Next to the CPU is a surface mount resisitor R138, gently remove this to open the new channels.

Resulting frequencies ranges are 26.065 MHz  - 29.695 Mhz

Frequency Expansion

240 Channel Operation

1)Put away the Golden screwdriver! No tools needed for this mod.
2)When Turning on the radio hold in the DW and channel 9 buttons.
3)To get to the 10 meter band hold in the LCR and MIC buttons.
4)To change bans press the channel 19 button.
5)Repeat this process to return to regular 40 Channel CB.

Unlocking the Clarifier

1) On the back of the clarifier pot follow the blue wire to the PCB.
2) Cut the blue wire about 1 inch from the PCB.
3) Find jp-44 and solder the blue wire to it.(its the 8vdc source)
4) Cut the resistor on the bottom of the clarifier knob.
5) Solder a wire from where the resistor was to ground on the PCB.
6) Finally jump D-40 and cut D-42.You should now have about 6Khz of slide.

Peak and Tweak

RV-7 AM Power
RV-8 SSB Power
Q-24 Audio limiter

Frequency Expansion

1) This is one of the more difficult mods out there.
2) Open the bottom cover of the radio .
3) Find the PLL Board. Its the one with the 64 pin chip on it.
4) At the front of this board by the PLL chip ther are 2 resistors R540 and R539.
5) Cut them.
6) Close the radio up. Turn it on.

Tweak and Peak

Audio limiter - R247
AM Power - VR 111
SSB Power - VR 103

RIT Modification

1)Remove top and bottom covers.
2)On the top of the main board find D140.Cut it.
3)Solder one end of a 10 OHM resistor to the location in the picture below.
4)Take a 7.5v zener diode and solder the end without the band to the small brass shield.
5)Now solder to other end of the diode to the open end of the resistor.

6)Find the PC Board that is behind the RIT Knob

7)Cut the trace as you see in the picture above.
8 )Solder a wire(See the green wire in the pics) from the point that the diode and resistor meet togeteher to the bottom of the board where you made the cut.

Aligning the RIT

1)Place the radio so that the smaller PC Board is facing up.
2)Turn it on and dial up 28.000 MHZ and put the rit dead center.
3)On the samller PC Board locate J502.(upper right)
4)Pull the grey cable off the board and connect it to your frequency counter.
(Sorry you can’t use them $49 dollar specials from copper.
You have to have a frequency counter with a probe on it)
5)Hook up the probe and if it should read 38.695 +/- 100 Hz.
6)If not then adjust L501.
7)Put the radio back together.You shound have about 6KHz of slide.

Channel Expansion

1)Remove top cover.
2)Behind the numder pad there are 2 black jumpers on a small board.
3)Move both of them from pin 1&2 to 2&3.
4)Find another jumper spot behind the channel display.If there is no jumper there then you can either put one ther or solder to 2 pins together.
5)Close up the radio and turn on.
6)Use the #1 buton to change bands.

Adjustments

RV1 RF Power Meter adjust
RV2 Squelch Level adjust
RV4 AM Carrier adjust
RV5 Modulation adjust
RV7 Modulation Meter adjust
RV11 13.8 Volt
RV12 S-Meter Adjust Both AM and SSB.
RV14 SSB ALC adjustment.
RV50 Clarifer Center adjust

Audio limiter

Remove small transistor under fm board next to diode D24.

Channel Expansion

1) Remove covers.
2) Locate a small PC board on the right side near the front.
3) There is a set of pins with a jumper over pin 1 & 2.
4) Remove this jumper and place it on pins 3 and 4.
5) Close up the radio and turn it on.

Adjustments

RV5 = AMC control
RV6 = ALC control
RV4 = AM/FM power
RV7 = Transmit Meter adjustment