IC-746 FAQ
dielectric. This will make it a lot easier to construct the input and output cables without
melting insulation.
The male PC connector is designed for crimp termination, but it can be soldered as well.
I just stripped the center conductor of the coax and (carefully) soldered it into the center
pin. I made a small pigtail with the braid and tacked it to the top of the shell. Be careful!
It's really easy to apply too much heat and displace the center pin. Once the assembly is
complete, check it with an ohmmeter to be sure it's not shorted.
The female PC connector is really designed for PC mounting, so it's a bit tricky to install
the coax. I took a small piece of #26 bus wire and wrapped it around the ground pins
and tack-soldered the shield to this wire. I then encased the junction in heat shrink
tubing to immobilize the connection.
Although it's a little close, the ends of the completed assemblies with the PC connectors
can be fished through the slots in the rear panel heat sink near the Key jack. The
assembly with the female PC connector is the T/R RX antenna output and the assembly
with the male PC connector is the RX input. Be sure that you have somehow marked
the pigtail assemblies so you know which is.
Once the pigtails are ready, it's time to install them. Pull the coax from J1 on the RF
board; this is the T/R switch RX output line. Reconnect it to the female pigtail cable
assembly. Plug the male pin from the other pigtail assembly into J1 on the RF unit. To
minimize the chances of mechanical problems, I used plastic tie wraps to bundle the
input and output pigtail cables together. Once the RF compartment shield is replaced, it
will hold the cables in place.
To check your work, power up the radio with an antenna connected but no connection to
the pigtail jacks. You should NOT hear signals in the receiver. Momentarily insert the
stripped end of a short piece of hookup wire into the RX input pigtail connector; you
should hear static and possibly signals. If all is well, connect a short RCA-RCA jumper
cable between the two pigtail jacks. You should have normal receiver function.
To insert a bandpass filter, overload protector, etc. in the receiver line, connect it
between the RX antenna out and RX in jacks. To use an external receive antenna,
connect it to the RX in jack.
Hope this is clear. Except for the fiddly process of soldering on the PC connectors, the
procedure is really pretty easy. Let me know if you need further assistance.
Increased MONITOR Volume
Unhappy with the volume level of the MONITOR, some have tried placing a 4.7K resistor in
parallel with R1087 to raise the level. There are more details on the www.mods.dk site at:
http://www.mods.dk/mods.php3?radio=icom&model=ic-746&selectid=2299
LCD Driver Transistor Replacement
Some folks have replaced the transistors that drive the LCD backlight in an attempt to
prevent overloading and burnout. See the question devoted to LCD lamps repairs for all the
gory details.
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2003-02-08
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