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Icom IC-736 (IC 736 IC736) DDS/VCO Bug/Fix
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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:
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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.
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tune the carrier to about 400HZ tone and listen carefully.
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switch to USB and back to LSB quickly. You should hear a different
tone. If not, then you are "floating" in the right direction.
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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.
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