Category: Fixing

I’ve been getting some complaints recently, about the audio from my Kenwood TM-V71A that I use in the car.

It has developed a ‘motorboating’ sound that sits at the back of my audio.

Strangely, it seems far more prevalent when I’m going through a repeater. No idea how that could be.

I had this problem a couple of years ago and a search on the internets showed that I wasn’t alone. Lots of people had the same issue with this rig. Research had shown that the culprit was the clock signal travelling between the microphone and the rig itself. That clock signal is needed for the keys on the mic to work.

A potential fix was to try re-crimping the RJ45 plugs on the mic cable. I tried this and sure enough, it worked.

But now the problem was back and I wanted a more permanent solution,

As I never use the keypad on the mic, the obvious solution was to just cut that clock pin. I have had the radio for about 8 years and have never used the keypad, but I know that as soon as I permanently disable it, I’ll need to use it for something.

And, so I decided a switch would be best, so I can disconnect or reconnect the clock wire as and when required.

Searching through my box of switches, I happened across a small tilt switch. I thought this would be a good idea, as the mic is in a vertical position when talking, but horizontal when keying something in. I drilled a small hole in the PCB to take the switch and wired it in: There are two circuit boards in the mic, with some wires going between them. The black wire is the clock wire, so I just cut that and lengthened it to reach the switch.

Turns out, it was a rubbish idea! The switch would activate at 45 degrees (of course!). Luckily, I had a very small slide switch, which fitted between the two boards quite easily. A small hole cut in the side of the mic casing and a dab of Superglue had it looking almost like it had been factory fitted. Almost.

Nonetheless, it does the job perfectly and my audio reports are “excellent” once more.

My Wouxon KG-UV8D stopped working the other day.

Two thoughts crossed my mind simultaneously:

“Oh bugger, I suppose I’ll have to spend out on a new handheld now”.

“Yay!  I can go shopping for a new handheld now”.

Still, being the curious radio amateur that I am, I decided to see if it was fixable.

A quick investigation showed the battery had run out of charge, despite it sitting in the charger for the previous 24 hours.  Hmmm.  I checked the charger, and sure enough, there was no voltage on the terminals.

I was somewhat dismayed when I opened up the charger and could see nothing immediately obvious.  Also, it was nearly all SMD… all too small and fiddly for my liking – I like proper components that you can actually pick up with your fingers.

Also also, I couldn’t find a schematic for it.

But, I started tracing voltages through anyway and it wasn’t long before I found a component with volts and one side and nada on the other.  Either a diode or a blown resistor, maybe.   It had no values shown on it, just the letter H.  A bit of research on the internets and some conversations with some fellow hams suggested it was most likely a 1A fuse. Bridging it with a piece of wire proved that to be the most likely case as the charger started working properly.

I didn’t want to leave the fuse bridged out – fuses are there for a reason after all – but a replacement SMD fuse on ebay was about four quid.  Yes, four quid! For a fuse!

So, I used a 20mm cartridge fuse of the right value, slipped some heatshrink over it and wired that in instead.

Put it all back together and it works a treat. No need to buy a new one.

Whilst trying to find a schematic on the internet, I read of many instances where this charger has failed, so I thought I’d write it up here for anyone who might have a similar issue.