Baofeng BF-666/777/888 audio mod + frequency adjustment

While I regarded the short review of the Baofeng BF-666/777/888 series as a side note, my readers apparently did not. Comments and questions rolled in, and it’s still one of the most read articles to date.  Personally I think they are quite fun to own; $25 isn’t much, and my dogs can’t destroy them while we’re playing in the park. After the first batch I bought another lot of them, branded Baofeng BF-666S, and distributed them amongst other hams.

Audio distortion
I immediately noticed that the RX audio was a bit raw and mentioned that in the review. It didn’t bother me much. A few days ago Tom PA2TSL bought two of my remaining BF-666S radios. He knew of the flaws, but couldn’t stand the audio distortion in the end. He started to experiment (strange folks, hams, trying to perfect a $25 hand held… it must be in our genes). We both looked at a few waveforms on our oscilloscopes and saw small, yet distinct ragged edges.

Finding the fix
The first thing Tom noticed is that the audio was fine on an external speaker. This could imply that the internal speakers are low quality, but when he connected an audio source to the internal speaker, it was fine too. Puzzling. Impedance problem? Something else? We discussed these findings on 2 meters, but all we could do was guess.

Tom checked the circuit board again and noticed something strange. The internal speaker wasn’t connected to PCB ground, while the external speaker was. After soldering the speaker wire to PCB ground, the problem was gone. This is what you have to do.

Remove belt clip and the 2 screws at the bottom.

Remove knobs and nuts

Carefully lift and pull the PCB out. Take it easy, the speaker wires are short.

Remove wire from position 1 and solder it onto position 2 (PCB ground)

Before – After

Tom also noted that one of the Baofengs was off frequency by a generous margin. Also easy to fix, see below. Don’t adjust this trimmer unless you own an accurate frequency counter.

While you’re at it, you might want to check the frequency accuracy.

Various notes

  • Don’t expect the Chinese voice to get much better – the sample is low quality by nature. Listen to other stations instead.
  • All PCBs we looked at needed some serious cleaning with alcohol. Strange white stuff there.
  • After the mod we both checked if there wasn’t a catch with programming or anything similar. We couldn’t find any. Have fun with the mod!

Hans PD0AC, Tom PA2TSL

Wouxun KG-UV920R volume mod

There aren’t many HAM operators yet who own the Wouxun KG-UV920R, but the first mods already surfaced. This one is might be interesting for people who want to use the radio in the shack. As is often the case with first runs of Chinese equipment, the lowest volume level isn’t really low. I didn’t regard this to be a problem for a mobile radio, and didn’t mention it in my review. Thanks to the efforts of VA3ISP Wouxun came up with a fix.

No details on the original resistor values, nor on the best replacement values, so you’ll have to figure it out yourself.

KG-UV920R Volume Mod. Click for large size.