Cobra 25, 29 Uniden PC 66, 68, 78 Talkback Mod

This is a easy $1 mod to add talkback to your CB Radio.
This will work for the following radios with no problems.

Cobra 25
Cobra29
Uniden 66
Uniden 68
Uniden 76
Uniden 78
and many more.

All you need is a simple resistor added to the bottom of the board, near the Ext and Pa speaker jacks.

Find the 2 solder points, closest to the rear of the radio, directly above the EXT and Pa jacks.
These are going to be the Negative or Ground side for the audio.

Solder a 1/4 or 1/2 watt resistor between these two solder points. Make sure that the resistor itself does not short out anything on the board or touch anything else. You can wrap it in tape, heat shrink or just keep it lifted slightly above the board.




Use a 100-500 ohm resistor.
The Lower the resistance is, the Louder it will be.
A 100 ohm will be Louder than a 470 ohm.
I like to use a 220 for most mics, or a 470 for good power mics.
You can also wire up a 1K variable pot to adjust the volume level.
You can also use a switch to turn it on/off, just wire it in series.
Ive used the Norm/Ch9/Ch19 switch as a Off/Low/Hi with 2 resistors, to make it adjustable for different mics or volume levels.


Thats it! Just 2 solder points for basic talkback.

XM Radio Mod / Hack - Pioneer GEX-FM903XM

This is the mod /hack for the Pioneer GEX-FM903XM tuner.

Open the case with the 4 screws.
Remove the screw for the heat sink for the Voltage Regulator transistors.
Remove the screw in the center of the board.
Twist the metal pieces along the edge of the board that are used as hold downs.


You can tap the audio in 2 different places.

#1. Tap near the 8pin IC near the center of the board, on the top.
There are 2 surface mount resistors, one above and one below the IC. They are both Grey in color . Tap the left side of each.




This will give you your Left and Right channel + audio.
You can get ground - from one of many place. You can use the center screw in the middle of the board, or one of the metal lids over the DIGITAL or ANTENNA modules.



#2 spot is on the bottom of the board.
There are some test points on the top left of the board.
Locate the 3 test points labeled:
RCH AGND LCH




These are the Right Channel, Audio Ground and Left Channel.
Simply tap all 3 of these for audio.


That is all there is to it, for getting RCA audio out of the Pioneer GEX FM 903 XM tuner.

Cobra 148 GTL Audio and Power Mods.

A simple way to really increase the audio of a Cobra 148 GTL CB radio is to find R126 and jumper it. It is a 10K ohm resistor about 1" to the LEFT of the MIC jack.
Do NOT remove the TR25 Mod Limiter on this radio, as it will sound like crap later.

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To add extra channels install 2 switches in the radio, or use the HI/LOW and BRT/DIM switches on the front.
My friend wanted 2 new switches on the rear, so thats what I did with this radio.

You will need 2 SPST switches.

Find the PLL IC and find pins 10, 11 and 12 and the large Ground trace near pin 10.

Wire Switch 1 to Pin 10 (pin goes to nothing) and also to GND pad.
Wire Switch 2 to pin 11 and pin 12.
Be very careful to not use too much heat on the IC pins, and they are fragile and you can damage the PLL chip. Use a 30watt max solder pencil.

Uniden PC 66 and PC 68 Audio and Power Mods

Here is a simple $5 way to crank your Uniden PC 66 or PC 68 radio to be a loud talker.

Parts you need.
35volt 220uf Electrolytic Capacitor
10 Ohm, 1watt resistor

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1st we'll do the audio.
There is no internal VR# adjustment pot to turn up on this radio, just on the front.
Doing a few small mods opens it up about 40% more audio. You may not need any power mic after this mod.

On the PC 66 look right below the mic connector.
On the PC 68 its on the front right side, near the edge fine these 4 parts.
R76 Remove and add Jumper wire across this.
R78 Remove (Added resistance on audio line to ground)
Q14 Remove (Mod Limiter)
C97 Remove (Filtered Audio to Ground)

This basically opens up the restrictions on the audio pre-amp circuit.

If you plan to use a good power mc, you might need to leave C97 in to reduce RF squeal or hum.
Some people prefer to leave the mod limiters in, to reduce splatter, but for a LOUD radio, I a remove it on this model.

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Next is the power output.
This is a touchy subject for some people, but I prefer to use "swing kits" in my radios.
I like to have my radio deadkey low, and swing high when I talk.
This add a lot more audio and "punch" to your voice.
What it basically does is lowers your output when your not talking, and raises it when you do talk. This reduces the power load on the radio, due to poor design, and "reserves" some power for your audio.

To add the swing kit, find JV17 in the back of the radio, in front of the Final.
Remove this jumper wire.

Now install your 35volt, 220uf Capacitor in this spot. Use the NEGATIVE side in the hole towards the BACK of the radio. Insulate the wire with tape or heat shirnk tubing to prevent it from shorting the metal nearby.

Now flip the radio upside down.
Find where you remove the jumper wire, and install the 1W, 10 Ohm resistor.

Now that you have installed everything, tune the radio. On most of these radios, you dont need to adjust the L10 coil, but some radios are off a little bit from the factory.
Spread the coils on L8 apart slightly.


You can also replace the c2028 Final transistor with a high power 2sc1969. This will be a great mod, if you can happen to find them, as they have been discontinued and are getting harder to find new.

That's it!
Thats the secret to tuning up a Uniden PC 66 or PC68.
Save yourself $20-50 at a radio repair shop, if you want to do this work yourself.