ICOM 706 MKIIG FIX

[Happy_Hamer]

I seen this on the net and checked my radio and it was starting to happen.

Today I realized my 706 was not transmitting, after checking the power I had only milliwatts coming out on 2 meters and 70cm, 6m and HF were unaffected.

I started crying softly thinking about the mosfet and me being without radio for a couple of weeks but to my surprise, there is no B+ at the mosfet collector and the device itself is not shorted in any way.

After checking the diagrams and the board layout, I took the board out and I realized the trace that supplies the power to the device is burned, like if the device would have short circuited.

I repaired the trace with a wire, reassembled the board and was happy to see the radio was fine.

What could have caused the trace to burn?

I reassemble the radio, put the cover on and connect... uh oh... SMOKE!

Took the cover out to discover that now the trace burned again but on the upper side of the board (my wire resisted)

Here is the cause:

There is some kind of shielding tape inside the cover that got loose/unglued with time and that came in contact with the collector coil as seen on the pictures.
This is a dead short and it burns the trace without burning the main fuse. I repaired the trace _again_ and remove that piece of tape.

Note the dent on the tape and on the coil, as well as the burned trace. The tape itself felt the heat

 

[Michael Bravo]

You have a good eye Hamer

 

[nightrider]

i agree

 

[Toll_Free]

I had a similiar problem on my (dearly beloved) TS440SAT.


These are the symptoms.

Was tuning it into a three-mag-mount located on a car in the garage. 11 meter antenna on it, 11 meters was the band. Hit tune and ant-tune switches, radio went into tune mode, and all of a sudden just stopped.

Power cycled. No TX, RX fine. Performed hard cpu reset. Upon power up, radio was locked in TX mode. Hit mic button, injected tone into mic and modulation was fine business!

Power cycle again, radio in RX mode. The only way it will TX AT ALL is with antenna tuner on, and in tune mode.

Now, I figured something in the CPU or in the tuner network (like a high-swr tx inhibit switching transistor stuck shorted or something)... hahahaha Yeah,right. Tear ENTIRE radio apart, then get bright idea to test microphone jack.

LOL

Seems Kenwood used the TX/RX switch (a dead key switch, I can only think was used to put radio in TX mode on CW to tune TL-922... WTF else would they put a dead key switch on the radio???) as a binding post as well for the MIC TX switch, the radio TX switch as well as the antenna tuner TX portion. Tear the ENTIRE front faceplate off, three levels, and find a binding post on the back of the TX/RX faceplate switch has shorted to ground. Move it a couple microns away, radio works fine business!

Another bummer found was on the middle sandwich board. Seems one of the inductors lost it's centertap solder... Cold solder joint or something.. Anyway, radio would lose RX, TX and would just motorboat. Flex center board, and problem goes away.

Resolder center tap on transformer, and I'm back in business!

--Toll_Free