Hardware Hacking

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.

Two published versions for this rig.. If you find the one that works for you please let me know so that I can update this mod.

Remove D8 on PLL Board Or clip D5 opens transmit.

Icom IC-706 Extended RX mod
From OH6LGM
Disclaimer:

I’m not responsible for any damage that may result following these
instructions. Remember also, that this modification voids Your warranty.
—————————————————————————-
Icom 706 doesn’t out of stock listen to frequencies over 148MHz, although
that is advertised. At Least mine didn’t.

Studying the schematics I noticed a front-end filter, that should be
operating in the range of 60MHz - 200MHz. I studied the filter with a
program and noticed, that the passband was 60MHz - 140MHz !! The upper end
was blocked out.

I changed the circuit in a way that enables the radio to work as advertised
by removing Capacitors C53 and C153. Now the filters upper edge is around
230MHz.

This modification doesn’t affect 2m RX in anyway, because 2m has its’ own,
thight front-end, that is used instead of the modified filter, when in 2m
band. HF and 6m aren’t affected either.

The Capacitors are found in the PA UNIT board, behind the external speaker
connector in a relatively easy place.

The job requires cautiousness because the components dislike static and
excessive heat.

This modification works, if the radio isn’t already modified with the
modification, which puts 2m front-end in use in frequencies above 144MHz.

At Least My unit worked well with this modification.
Measured from my IC-706:
Frequency Sensitivity (microvolts /20dB SINAD)
60-140 0.14
144-148 0.12
150 0.18
155 0.15
160 0.2
165 0.3
170 0.4
175 0.6
180 1.5
185 1.5
190 >100mV — deaf!
195 5
200 29