Low modulation fix Baofeng UV-5R using built in VOX preamp transistor

If your baofeng UV-5R radio suffers from low transmit audio or low modulation this modification will help in improving your modulation problem. This fix will use your radio VOX preamp transistor to amplify the audio from the radio electret condenser microphone. Using this modification will disable your VOX function so don´t do this modification if you want to use your radio VOX function. As I have no use for it and I am not satisfied with the VOX sensitivity, I preferred this modification which was originally done by PA3FYM. This modification is different from I recently published modification by DG2IAQ which simply replaces and remove some of the capacitors on the UV-5R board.




The modification by DG2IAQ can be found here: https://drive.google.com/file/d/0B0…





If you want to retain your VOX functionality follow the modification by DG2IAQ. Since I have no use for the VOX function and the surface mount devices are difficult to source here locally, and the available components I have are too big to fit under the UV-5R LCD I will do the modification by PA3FYM which just require a single resistor with a value of 500-1000 ohms to couple the transistor emitter to ground. I use a donor board of an old VGA computer card to source the resistor and I found a 900ohms surface mount resistor which is just perfect for this modification. It is important to have the right tools for the job as it is difficult to work with surface mount devices and the UV-5R board is easy enough to damage with an over heated soldering iron, but of course you can do it with soldering iron alone with a little difficulty. I have a rework station and a little experience in handling surface mount devices, but still it is not a walk in the park.


Donor board a VGA card, twizzer, sharp blade, soldering paste, flux. screw drivers and rework station

The modification of PA3FYM. (Do this at your own risk). The schematic of UV-5R radio can be downloaded from the link here on my Google Drive.

PA3FYM
PA3FYM low modulation fix using UV-5R VOX preamp

The transistor involve in this modification is a 2SC1623 general purpose audio frequency amplifier on SOT-23 package mark as L6 on the UV-5R board. We need to lift the emitter and connect a 500-1000ohms resistor to ground. I found a 900 ohms resistor from the VGA donor board and itś just perfect for my use.

The data sheet of the transistor can be found from this link for reference:

A knowledge in reading the schematic is useful when cutting the tracks on the PCB between the inductor L44 and capacitor C137. The track is in the middle of those two components.

voxmod

This is my modification magnified

Modification on my UV-5R radio

Make sure to test your modification before assembly to make sure your radio will still work. So I did…

perfect

So luckily the operation is perfect and radio is still able to power on 🙂

I have tested the changes and the radio is now sensitive in picking up my audio even if the radio is more than 6 inches from my mouth.

The original thread of the modification can be found from this site:

Good luck on your radio modification. Cheers! de DW1ZWS.




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