A fellow ham approached me with a defective Kenwood TM-D700A transciever. The unit showed no signs of life. There was no display, and no response to pressing the power button. The only hint was that the cable between the radio and remote head had recently been repaired.
Luckily, I have the service manual for this radio. It was essential in this repair. After checking the obvious (making sure that power was getting to the radio), I decided to check that power was getting to the remote head. In order for the soft power switch to operate, there is a constant supply to the remote head. There should be 9.66v between pins 1 and 4 of the remote head cable. In this instance, there was no voltage at all. A simple power supply around D903, Q910, Q911 and Q913 creates the 9.66v signal from the raw 13.8v. Again, no voltage at all. The supply is protected by fuse F902. This is a 1.8A tiny surface mount fuse. Without the schematic, I probably wouldn’t have found it. It’s located just below the voice synthesizer connector (see rather bad camera phone picture). I was unable to locate such a tiny surface mount fuse, so I replaced it with a 2A picofuse. I carefully bent the picofuse leads to attach to the original solder pads. A small dab of glue gun glue held the fuse up off of the circuit board to avoid any shorts.
After re-assembling the radio, all functionality checked out. I suspect that the original damage to the head cable caused a short which blew this fuse.
THANK YOU!!!! I purchased a Kenwood TM-D700 on e-bay and it would not turn on I was searching for a repair center to ship it to but I found your website and you pointed out the EXACT issue with my radio. I bypassed the fuse (F902) and the radio started working like it should be. I have ordered the Pico fuse that you recommended and am waiting for delivery. Thanks again for a great web site
Hello, I have been searching for some help with my D700. I have checked all the potential problems that I have seen on the internet and my unit doesn’t have those issues. The connecting cable is supplying power to the control head and I have 8.88V after the diode and 5V coming out of the transistor right next to the diode. So from that point, I don’t know what to check or troubleshoot to find the problem. Do you have any suggestions?