AND REPAIR OF ICOM IC-R70 AND IC-R71 RECEIVERS
March 19 2000
Almost all modification and service instructions required by a
"normal DX listener" have now been added to these pages.
Among others, there's more about battery replacement, display
problems and 12 V DC connection.
article I'll concentrate mainly in the IC-R71, which seems to
be much more common than the older R70. Even though the R71 is
over 10 years old, completely unmodified units show up now and
picture, the original memory card is being replaced by an ICM-1024
memory card - probably already difficult to purchase these days.
With the new card, the number of station memories is increased
significantly and the "muting problem" caused by an
empty battery is fixed.
the battery voltage drops to a critical level, random malfunctions
usually show up. The malfunctions are often mistaken for other
types of faults, so it is advisable to always check the battery
first. For example, in some units, a wrong front-end band filter
will be selected.
modifications are considered mandatory by DX listeners, and the
notch and RF-amplifier have often been modified right after purchase.
There seems to be no reason why the notch shouldn't work also
in AM mode, and similarly, anybody can switch the RF amp on and
off using the front panel switch even on the MW band. Obviously,
Icom considers the AM listener to be an idiot, who thinks that
the RX is faulty if the receiver overloads on MW or if the notch
control is in the wrong position.
the past years, I have modified and repaired over a hundred R71's,
and less than ten R70's. During this time, I have noted some typical
TYPICAL FAULTS IN IC-R7X RECEIVERS
Icom IC-R7X many problems have been caused by bad solder connections
- always keep that in mind when looking for faults.
problem is a large shift of the BFO's frequency. In many receivers
the adjustment range of the BFO's USB trimmer is insufficient.
I have carefully cut off a piece of the ceramic trimmer, to get
a smaller capacitance. The USB crystal is located too near the
af amplifier heatsink, causing a long warm-up time before the
frequency stabilizes. A piece of styrox can be added between the
af power amp heatsink and the BFO frame to reduce heating of the
frequencies should be checked and adjusted when necessary, to
place them correctly on both sides of the IF center frequency.
If misadjusted, zero beat on AM is not at the correct frequency
reading, and the BFO frequency is incorrect with respect to the
IF passband, which is especially noticeable on smaller bandwidths.
is located right behind the audio section when wieved from the
front. The BFO unit can be identified by it's two crystals. Let
the receiver warm up an hour or two before making adjustments
and keep the lid or other object on top of the receiver to reduce
heat transfer. This ensures that the adjustments are made as close
to normal operating temperature as possible.
the BFO, you'll need a frequency counter that is accurate at least
to the 10 Hz digit at 9 MHz (1 ppm). Connect the counter to R139
and set the receiver to USB mode. If the frequency deviates more
than few tens of Hz from 9013.0 kHz, carefully adjust C78 using
a non-metallic screwdriver. You should be able to get within a
few herz of the correct frequency, at least for short term. LSB
frequency is adjusted to 9010.0 kHz with coil L20. If needed,
RTTY mode can be adjusted with coil L22 to 9008.475 kHz. CW mode
has no adjustment; the frequency should be 9009.8 kHz +/- 200
service note promises a 5-fold improvement in BFO stability by
gluing a PTC resistor to the BFO crystal and feeding the resistor
from the 13.8 volt supply rail.
SYNHESIZER FREQUENCIES AND VOLTAGES
to BFO adjustments above, reception quality and frequenqy display
accuracy can be improved by correct adjustment of the synthesizer
section. In older receivers, which may have been in use for 15
years, the synthesizer adjustments may be off their optimal values.
This is easy to check and re-adjust using a frequency counter,
digital voltmeter and an RF voltmeter.
context it may be noted that if you have an Evdis PLAM board,
do not perform adjustments according to the instructions that
come with the Edvis board. This will cause SSB carrier frequency
to be off by 150 - 300 Hz with respect to the PLAM mode. Instead,
you should first adjust the synthesizer in SSB mode according
to Icom's instructions, and after that, adjust the PLAM mode using
only the trimmer on the PLAM board. When adjusting the PLAM, do
not touch trimmer R20 on the matrix board (this trimmer is on
the bottom side of the receiver, right under the VFO).
operation of the main frequency control (VFO knob) may be caused
by malfunctions in the pulse encoder and it's associated electronics.
When the frequency control knob is rotated, this encoder outputs
signals SV1 and SV2 to connector J6 on the logic board, which
resides under a shield plate on the bottom side of the receiver.
checked with an oscilloscope, these signals must be 5 volt square
waves with a 90 degree phase difference. The frequency of the
square waves depends on the rotation speed of the frequency dial.
The phase difference carries information about the direction of
rotation. This same principle applies to almost all modern receivers
with a pulse encoder (optical or otherwise) on the VFO shaft.
case, a frequency dial problem was caused by a bad solder connection
in the tuned circuit between pins CLK1 and CLK2 of IC2 on the
logic board. This made the oscillator run on a much lower frequency
than normal, causing slow and intermittent operation of the main
in the power supply has caused some problems. It is worthwhile
to check the mains transformer primary voltage setting and set
it to the highest voltage available (240 V / 120 V). In the original
circuit, voltage after the rectifier bridge is close to the maximum
voltage of the filter capacitor. The bridge may also run real
hot. It will cause no harm to replace the rectifier bridge with
a larger and better cooled one.
advisable to install insulation tubing over the leads in the mains
primary circuit. These leads run in a confined space between sheet
metal and the PCB's foil side. This can produce quite a catastrophe
if mains voltage is short circuited to the low voltage parts of
the receiver - for example, when a power supply fault causes enough
heat to melt the insulation, or a component lead on the PCB punctures
joints on the power supply PC board have caused various problems
- mainly in the power transistor and rectifier bridge. The construction
is such that especially the power transistor's solder joints are
subject to mechanical stress during transport of the receiver.
of the solder mask around the rectifier bridge's solder joints
should be scraped off to make the solder connections larger and
picture above, you can see the rectifier bridge solder joints
which do not look too good. You can also see how difficult it
is to make the solder flow properly in the small soldering pad
area, so the scraping mentioned above is in order.
receivers, the external 12 VDC connector on the back plate is
not installed at the factory. Installing the connector requires
some clever juggling. Obviously, the hole in the back plate is
not meant for this kind of connector, or the hole is machined
wrong. Using cutters and a file, it is possible to install the
connector. Note that when the receiver is operated from the mains
supply, a dummy plug must be installed in the connector. It's
purpose is to connect the output of the mains power supply to
the receiver. If you do not have the original DC supply lead,
it is possible to use the dummy plug to construct the supply lead.
If you want to do so, first remove the short circuit loop from
the plug. Then connect and external 12 DC supply to the plug,
with positive terminal on the side with a pointed edge, and negative
terminal on the side with a flat edge. The two center pins must
4 - 6 amp fuses in the DC lead. In mains operation, you must re-install
the short-circuit loop.
receivers the display causes disturbance (false signals) in reception.
This problem is often alleviated just by moving around the cables
close to the display to minimize display noise. A factory service
note advises to to cut a blue lead (W6, connected to pin 6) from
the display unit and to insert a choke in series with it. The
manufacturer of the choke is Taiyo Yuden, type LAL04NA820K. You
may also experiment with other chokes in the 1 mH range.
THE MEMORY BACKUP BATTERY
the sheet metal plate on the underside of the receiver. Under
it, you can see a PC board with a daughterboard, which contains
a RAM chip and the battery, which is soldered in place. Icom has
used at least two different kinds of RAM.
the daughterboard by unscrewing the small phillips head screw
and pulling the board out of it's connector. Measure the battery
voltage - for data retention, it should be over 3 volts. The voltage
does not provide an indication of how soon the battery will be
completely drained - this kind of battery will have almost full
voltage up to the end of it's life, after which the voltage drops
replacing the backup battery, connect a 3,5 volt source in parallel
with it, so the RAM will have uninterrupted operating power throughout
the replacement procedure. It is worthwhile to connect the source
far enough from the backup battery, so you won't melt the solder
connections while soldering the backup battery.
cannot obtain an identical replacement for the battery, you can
improvise and use another type of battery, as long as the voltage
battery (and therefore, also the RAM) is already empty, the radio
will not be operative. The RAM board must be sent to a repair
shop for replacement of the battery and reloading of the software.
This shouldn't be very expensive, but it is advisable to check
the cost before sending the board. The board should be back with
you in a few days, equipped with a new program that (at least
in theory) enables you to receive from 0 to 50 MHz.
quality of IC-R71 leaves something to be desired. While not an
expert on this subject, I have in some receivers changed the loudspeaker
coupling capacitor value. Kiwa Electronics (US) has a modification
kit for improving the audio.
COMMON - AND MOST NECESSARY - MODIFICATIONS
IC-R71 modifications in short:
1. The RF-amplifier can be forced on by cutting diode D23 in the
RF-unit, which is located on the right hand side of the receiver.
2. The low band attenuator can be disabled by shorting R11 and
R12 and cutting R13 in the aforementioned RF unit.
3. The notch can be made operative in AM mode by changing the
circuit as in the following diagram.
MEMORY CARD ICM-1024
the Willco Electronics memory card is no longer available as new,
I have attached a few pictures of the connections. In one case,
it turned out that an uninstalled memory module was at hand but
without any documentation.
following picture you can see how the memory module is connected
picture, an example of switch wiring
a list of connections to the IC-R71 receiver
complete documentation is available from the webmaster upon request.
designed several alternatives for switching the IF filters. In
the original circuit, although there's a filter selection switch
on the front panel, filter selection is also controlled by the
mode selection. This is somewhat limiting.
more options in selecting filters, some modifications around IC3
on tha main board are necessary. All filter combinations are not
useful in DX-listening, so the modification presented here is
limited to three choices, which should be quite sufficient. Four
choices could be made available, but this would not provide additional
value unless actual filters were also replaced.
is probably best described as a series of steps as follows. In
addition to tools and wire, two diodes are needed - 1N4148 or
1N914 will do.
is performed on the main board, in the vicinity of IC3 (4051)
diodes D41, D42, D47, D49, D50, D51 and D52
2. cut the cathode leads of D44 and D43, and solder the cathode
of D44 to where cathode of D43 was
3. solder a new diode from pin 13 of IC3 to the cathode of D44
4. cut diode D40 and solder it's anode to IC3 pin 13
5. cut cathode of D39 and solder a new diode from pin 1 of IC3
to where the cathode of D39 was
6. cut diode D33 and solder it's anode to pin 1 of IC3 using an
7. turn the filter switch to position "on"
now have three combinations of filters available. The functioning
of this modification is explained in articles found in the list
of magazine articles (DX-Kuuntelija and Radiomaailma, in finnish).
users have not been satisfied with the performance of the original
IF filters. Relatively high-priced replacement filters are available
for both of the two last IF's. The wide filter can be considerably
improved by replacing it with a narrower one of higher quality.
A suitable bandwidth would be 3-4 kHz, depending on personal preference.
Space is provided on the PCB for a FL-44A crystal filter for improving
the SSB mode. Before installation, the original filter must be
removed. An old Herz brand filter will fit, if you can locate
one; please note that in this case, isolation capacitors must
be installed due to the different internal construction of the
Herz filter. The PCB foils leading to the filter must be cut and
bridged with 10 nF capacitors. The value of these capacitors is
replacing the wide filter with a new and preferably metal-cased
filter, the larger filter will not fit in the original filter's
space. It can be mounted by soldering carefully at both ends to
the shield plate adjacent to the filter area. You'll need to bend
some components to make the filter leads as short as possible.
Connect together the ground pins of the filter and the pin connected
to the filter's case. Use insulated tubing where the filter leads
pass close to other component's leads. You can also install the
filter on the foil side of the PCB, provided that it does not
hinder the board's installation back into the receiver.
filters are Murata CFS- and CFK-455 series models "I"
(4 kHz) and "J" (3 kHz). The CFS-series filters may
be difficult to obtain as new, but they, as well as the Herz filter,
can be found in some modified Trios.