Hardware Hacking

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

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

Clarifier Modification Version 1

STEP 1 Remove top and bottom cover.

STEP 2. Prepare a small gauge jumper wire Tin both ends.

STEP 3. Remove the 1K ohm chip resistor on the radio front panel (it is R306 see pic below for a diagram)

STEP 4. At the removed resistor location, solder the prepared jumper to the pcb pad nearest the center of the radio.

STEP 5. Solder a 1K ohm 1/8 watt lead resistor to the other end of the jumper (a 1/4 Watt will be OK).

STEP 6. Solder the free end of the resistor to the emitter lead (lead nearest the rear of the radio) of Q61 (which is the main voltage regulator).

STEP 7. Turn the radio over so the bottom of the pcb is facing up and the front is closest to you.

STEP 8. Locate chip resistor R63 (a 1 KOhm) and remove

Explaination:
The 8V RX only supply is removed from the clarifier by removing R306, the jumper that is attached to the pad supplies the clarifier with a constant 8V, this allows the clarifer to work in TX as well as RX, the 1K 1/8th watt resistor is installed to protect the power supply.

R63 is removed to……

(As you can see there is some text missing from above, it may be because some people can not find R63 and it may be due to a slight design change, if you can help with this let me know)

Clarifier Modification Version 2

REMOVE: R306, R105, D27&27A
JUMPER: R305, D27A

R306 is 1Kohm & is located on front PCB, R305 is 6.8Kohm and is located on front PCB, R105 is on the Main PCB bottom, D27/27A is a three legged Diode located on the Main PCB bottom.

Prepare a 6″ jumper wire and attach a 1/8 watt 10Kohm resistor to it (insulate the connection).

Connect one end to emitter of Q61 (leg nearest rear of unit).

Connect the other end to the solder pad nearest the center of the radio that was left vacant by the removal of R306.

Tune AM, LSB, USB with T14, 15, 16 to same location on clarifier.

Center clarifier by tuning can that is nearest front Main PCB left corner next to the crystal.

This transformer has different numbers in different production runs as do T14-16.

Once clarifier is centered it should slide 10KCs but may drop out on one end or the other so be careful!

The unit I modded put out a solid 25 watts PEP SSB and I did not do the NPC mod because it was not going to be used on AM very much.

BTW, you can increase the mic gain by changing the value of R138 to 150Ohms instead of 270Ohms, play with this value because too much gain will cause oscillation.

Good luck with all of this.

Take your time to study the schematic and the radio until you have identified all the components in the clarifier circuit before you begin the mod.

These radios are all slightly different depending upon time of their production run.

240 Channels

Press and hold “DW” and “9″ then turn radio on. Select bands by using the “CH99″ button. To set for 28Mhz to 29.7 Mhz press and hold “LCR” and “MIC” then turn radio on. To switch back to 40 channel mode repeat process.

Modulation boost

One Chip resistor R138 controls mic gain, decreasing the value of the resisitor increases the gain. Its best to use 270 Ohms, but the value can be as low as 150 Ohms.

CAUTION!!

If too much gain is used oscillation may occur.

Various Mods

To disable the power limiter remove Q33.

NPC mod: Connect a 1N4001 diode/100ohm resistor in series.

The diode cathode(banded end) goes to the collector (center leg) of Q75.

The other end goes to the junction of R228 & R243.

Modulation limiter can be defeated by the removal of chip resistor R148.

Optional: Use VR10 to set the driver bias to 50ma.

Check that the final bias is at least 100ma.

Remember there are 2 finals. You will have to use a schematic to locate components.

There are two printed ciruit boards for the 77-285.

You must first determine which you have.

Circuit board “A” This board can be identified because D18 has been cut.

To restore full power simply resolder D18 or replace it.

Circuit board “B” On the “B” circuit board D18 is intact (has not been cut out).

To restore full power, locate D18 and trace the etch. Put a solder bridge between the open pads.

Channel Conversion

STEP 1. Take the bottom portion of the case off and unplug the speaker.

STEP 2. With the bottom of the case off, turn the radio over and in this position the Midland name should be upside down. Tilt the chassis forward toward the face plate. As you look at the inside panel the LC7232 IC chip should be readable and pointing toward you (upper right corner).You need to open solder bridges 5 and 6 from left of the chassis(bottom left).

FM Conversion

Removable battery pack.
Remove casing.
Locate solder pads (there are only two that look like jumperable pads).
Solder the top two together.
You now have FM