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                                                        ICOM IC-738

                                                       EXPD RF .5 - 30.0 Mhz

1- Remove power and antenna.
2- Remove screws and remove cover
3- Locate logic board (front of radio).
4- Locate and move D-15 to near connector.
Diode D-14 is the expanded RX diode make sure it is removed.
5- Reassemble the radio.
6- Reset the microprocessor if required
 

                                  

 

Speed-up the ALC for IC-736 / 738

 Hallo, my name is Claus and the QTH is in Rastatt nr Baden-Baden South-West Germany. I got a IC 736 in December 1994. It is a good rig but had also a lot of misstate. After a time of measuring and testing I found the ALC for transmitting is to slow. So I jacked the circuit why is so. I found a C-R delay in the way from the ALC on the Main Unit. It is the C287(1uF) and the R305(150Ohm). The C change or put out is not very easy. So I change the Resistor 305 in to smaller one. But the result was not better. The best result I had without it! So the C-R combination is not in the work for the ALC. The Resistor 305 is very small but it is easy to put out. On the Resistor is the number 151 printed (150Ohm) but you mast find it on the circuit.

To be wide TX you mast only cut the Diode D15 on the Logic Unit.

The IC 736 works very well at the last half year so I send it out in the PR-news now.

Icom IC-736  / 738 DDS/VCO Bug/Fix.
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