The AM Forum

Anyone familiar with this little beast and its power control circuits?  I use it in my car and one day it would not turn on and has been that way ever since.

TNX
~ps

Check the fuse?, DC connection?, tried it on an external power supply? etc.

There is a website that a guy does some improvements to the IC-706 and the very first one is aimed at a power-up problem and how to fix it; but I can't remember the web addy. I stumbled upon it doing a web search. If memory serves me correctly, he was located in Europe.

Phil

I have serviced a few of them and have two, and I don't like working on them very much. That problem could be a variety of things, best get the schematic and if it is not a simple 12VDC issue, start with the power supply to the processor. Note it can be a bad connection on the (-) side as well.

Also,  if you can run the rig from an external 13.8 ish volt PS,  you should hear a fairly silent,  but noticeacle click of a relay when you first turn on the PS.  Think that this is the way Icom protects most of the radio from reverse polarity.  If you do not hear this quiet click,  then there is something in the DC cord,  fuses or very close to the power entry circuitry inside the rig ... if this clearly written (?).

Sure a neat lil compact rig.  Must be fun to bore into the guts of one !  73  GL  Vic

Make sure the faceplate contacts are clean. Mine goes dead a couple times a year in my truck from this.

This may be of assistance -->> http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=17881



ICOM IC-706MKIIG Tech Notes

Loss of "HV" voltage:

If your IC-706MKIIG will not power up (and you've ruled out the DC cable and power supply), check the state of the "HV" line. Sometimes, surface-mount resistor R591 (under the PA Unit) will open, due to a power supply surge. And I have seen quite a few rigs where the rubber pad under the PLL Unit caused corrosion of the "HV" trace. Apparently, some kind of chemical reaction is taking place with the self-adhesive film between the rubber pad and the circuit board. Maybe it only happens in humid or damp environments. I'm not sure. But I've seen this happen to quite a few MKIIG's.

Here is an example of the affected area, with the pad still in place:


Here is an example of the affected area, with the pad removed:


Here is an example of the affected area, bypassed with a jumper wire:


Unstable VCO or PLL Unlock:

Another common problem is VCO instability or PLL unlock. The symptoms can be intermittent distorted or garbled audio, affecting receive and transmit, or complete loss of RX/TX. The MKIIG has four VCO circuits, each one has a trimmer capacitor. Often, these trimmer caps will become unstable. Sometimes, giving the offending trimmer a few twists, then realigning to specs, will resolve the issue (at least temporarily). But replacing the trimmer is often required. And then, it is best to replace all four of them. It's not an easy job, since they are surface-mount types, located inside cramped metal shields.

The reference VCO affects all bands. Its trim-cap is C4 on the PLL Unit.
VCO1 affects 0.03 to 29.999 MHz and 60.0 to 128.999 MHz. Its trim-cap is C306 on the PLL Unit.
VCO2 affects 30.0 to 59.999 MHz and 129.0 to 199.999 MHz. Its trim-cap is C335 on the PLL Unit.
VCO3 affects 400 to 470 MHz. Its trim cap is C367 on the PLL Unit.
To replace trimmer C4, shields MP5 and MP7 can be temporarily removed. To replace the other 3 trimmers, coils L302 and L332 can be temporarily removed, since removal of shield MP12 is much more difficult.



Varying TX output from band to band (HF and 6M only):

If your MKIIG has vastly varying transmitter output from band to band (into a dummy load), suspect surface-mount diode D9 and/or D10 on the Filter Unit. Usually, D9 is the only one at fault. These diodes are in the SWR-sensing circuit. They're accessible without removing the filter board.

D9 and D10 are shown in the top-right corner:


NOTE: If you don't have the skills or equipment to work with static-sensitive surface-mount components, please leave it to a qualified technician.

Mike Nadeau - N1EQ
www.n1eq.com

Last updated: December 27, 2008

The links to N1EQ's site is a good start, if you must/need to send it away, I highly recommend sending to
Mike, N1EQ. Email him first to see what his schedule is. I sent my 706 to get the SWR circuit repaired (SMS stuff is REALLY small... )
3 day turnaround time and decent repair cost....
Just a satisfied customer ....

Good Luck
Rich
n2ry

TNX all for the good info.  Looks like a good place to start.

~ps

Mike resolved a similar power up problem on my Yeasu FT100D a few years back.  He does great work and charges fair prices.  Unfortunately he has decided that he will no longer work on certain Yaesu models, including the FT100D.  Mine presently has a PLL problem very similar to the one described above on HF below 15.000 MHz and in a chunk of spectrum that includes the 2 meter band.  I am probalby going to ship it out to Burghardt in ND, they appear to have a good rep for Yaesu work.  I have tried reseating all the connectors in the radio and examined the master oscillator board for any obvious visual problems, but that's as far as my 57 year old eyes can take it.