Hardware Hacking

For all those who wants a little more of driving power for
an old amp with the new IC-746,here is the way to do it
easily.
Important settings pots within the IC-746 HF/VHF radio.
Remove the twelve screws holding on the bottom cover. With
the Radio laying flat on it’s top remove the bottom cover.

Underneath the radio there is a board named MAIN UNIT
(B5083J) where there are 4 important small pots provided
to increase or decrease the power output in different
bands as follow:

R-989 HF Power output (rated at 100W)

R-991 50 Mhz band Power Output (rated at 100W)

R-993 144Mhz band Power Output (rated at 100W)

R-994 AM Power output (rated at 40W)

R-546 Tx gain,set at factory for best linearity in TX IF
(better not to play with it)

This is the mod for an IC-746 with the diodes in the 1, 2, 4, 6, 9 and 14
position and the description below explains this.

! IMPORTANT !

There seems to be new version of the diode pattern out there with diodes in
the 1, 3, 4, 6, 7, 10, 11, and 14 position and the mod DOES NOT work for
this pattern. If you find this pattern after reading the mod below, DO NOT
try it. It DOES NOT work. If I find the mod for that pattern I’ll try to
get it posted here also.

Remove the twelve screws holding on the bottom cover. With the Radio laying
flat on it’s top remove the bottom cover. Turn the radio so that the front
panel is to your left and the antenna connectors are to your right. Locate
the IC labeled “ICOM HD6433042SF”. About 3/4 of an inch to the right is a
vertical row of diodes. The left hand column of diodes has 7 diodes (14
possible spaces). The right hand row is full with 14 diodes. Remove the
diode in the 6th SPACE from the top in the left hand column. DO NOT remove
anything from the right hand column. This should get you TX from about
100KHZ to 60MHZ and 118MHZ to 176MHZ. Do this totally at your own risk.
Never, ever transmit out of the ham bands or your privileges..

Remove the twelve screws holding on the bottom cover. With the Radio
laying flat on it’s top remove the bottom cover. Turn the radio so
that the front panel is to your left and the antenna connectors are to
your right. Locate the IC labeled “ICOM HD6433042SF”. About 3/4 of an
inch to the right is a vertical row of diodes. The left hand column of
diodes has 7 diodes (14 possible spaces). The right hand row is full
with 14 diodes. Remove the diode in the 6th space from the top in
the left hand column. DO NOT remove anything from the right hand
column. This should get you TX from about 100KHZ to 60MHZ and 118MHZ
to 176MMZ. Do this totally at your own risk. Never, ever transmit out
of the ham bands or your privileges..

GENERAL COVERANGE IN TRANSMISSION.

1) Remove the top and bottom covers of the transceiver.

2) Remove the final power amplifier module.

3) Locate the LOGIC-UNIT on witch there is a back-up lithium battery for the RAM memory.

4) On the LOGIC-UNIT, near the chip called IC6 (TMP82C265BF-2), between the output pin PC06 and the imput pin PA15, find the diode D3.

5) This diode is not an SMD component.

6) Cut the diode D3.

CW Filter Switching Modification for the Icom 737

MODIFICATION

1) Remove the top/bottom cover of the radio as per the manual.

2) Position the radio facing you and locate the resistor R-323 which is
simply labeled “323″ on the PC board just to the left of the opional
455 Khz CW filter. Solder a wire to the end of R-323 which is closest
to the front pannel.

3) Locate J-3 just above and to the right of the 9 Mhz filter F-13.
Attach a wire to the connector or wire going to pin 7. Pin 7 is the
third pin from the right. (The pins are numbered 1-9 from left to right)
You may carefully tack solder a wire to the plug by removing it first.
I used a solid 28 gauge wire and just pushed it into the connector without
soldering.

4) Replace the top and bottom covers.

1, Remove power, antennas etc.
2, Turn rig upside down with front of rig facing away from you, remove bottom cover
3, Looking at the back side of the front panel “logic board” just to the side of center, along the bottom (actually now at the top) you’ll see diode D15, this is a typical non-surface mount glass diode.
4, Clip this diode.
5, Reassemble rig.

Mod complete.