Icom IC-736

DDS/VCO bugfix

I came accross the problem here:

As the link may not work in the future I quote the text here:

I have just received confirmation from ICOM Canada that there is a bug in the design of the IC-736 with respect to frequency generation. It seems that although it seems to be a common problem, not all IC-736's exhibit the problem. It seems that there is a "floating" data/address line and at times it floats the wrong direction, giving about 30HZ (maybe 32HZ?) difference in LSB mode. The fix is to solder a 47K resistor between pins 17 and 10 on IC24 on the main board. (bottom of radio, near front). I have not yet tried the fix, as I just got it today.

To see if you too have the problem, try the following test:

  1. switch to AM first and tune to a strong AM carrier, and switch to LSB (once and only once) 40M is a good place to try this.

  2. tune the carrier to about 400HZ tone and listen carefully.

  3. switch to USB and back to LSB quickly. You should hear a different tone. If not, then you are "floating" in the right direction.

  4. switching to USB and back to LSB will not produce any more differences. You must LEAVE SSB mode (ie AM) and come back to LSB for the first time to re-set the "floating" line. It is the LSB/USB/LSB switch that shows the difference in the two LSB received frequencies (by tone only, the display does not change...)

I've tried to post this message about 4 times so far with no apparent success. Hopefully this one will make it....73's and hope that helps someone

Steve, VE3CWJ

I excercised the procedure described above and indeed the frequency jumped of the 30 Hz, or so. The remedy is very simple, read the text above.
I found 100K rezistor is sufficient to do the trick, at least in my case.


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