Modifications for the Icom IC-R71

Picture(s) of Icom - IC-R71

19-07-1998 Tricking the ICOM R-71A to tune below 100 KHz English language
19-07-1998 Modifications to the Icom R71A IF filter selection circuit English language
19-07-1998 Here is the R-71 version of the Drake R7/R8 type passband tuning system English language
23-08-1998 R-71A Memory Notes English language
30-03-2001 RAM Card Backup Battery Replacement Instructions English language
18-11-2001 RAM board programming interface & R71A modification English language

19-07-1998 add a comment
Tricking the ICOM R-71A to tune below 100 KHz
Author: Bob Parnass, AJ9S - parnass@megsinet.net.MODIFICATION.NET


The ICOM R71A general coverage receiver is designed for VLF reception down to about 97 kHz.

The following steps will confuse the microprocessorbased controller sufficiently to permit reception down to 0.0 kHz:
  1. If all 32 memory channels contain frequencies, use the FUNC and CLEAR buttons to clear a memory channel.
  2. Place VFO/M switch into the M (Memory) position.
  3. Using all the manual dexterity you can muster, rock the MAIN TUNING knob back and forth, while simultaneously rocking the MEMORY-CH rotary control to switch back and forth between a memory channel with a frequency in it and a clear memory channel.

    Continue rocking both the controls until a frequency of 0.000.0 appears on the digital display.
  4. Depress the WRITE button. This stores the 0.000 MHz frequency in a memory channel.

    You can now rotate the MAIN TUNING knob clockwise to tune up from 0.000 MHz to the frequency you want. Be careful: if you rotate the MAIN TUNING knob counterclockwise, the radio will immediately revert to 29.999 MHz.
To tune below 100 kHz in the future, just recall the 0.000 MHz frequency from the memory channel and use the tuning knob to tune upward. That way, you don't have to use two hands every time you tune to a VLF frequency.

I used a Wavetek 180 sweep/function generator to verify that the R71A is indeed receptive to signals below 100 KHz.

Date: 17-07-2002 User comment From: Paul - G7VAK
Subject: Tricking IC-R71 for LF reception

This simple 'mod' also works on the IC-R71E.
Excellent mod and excellent copy on 60kHz!
73 Paul

This modification has been read 2249 times.

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19-07-1998 add a comment
Modifications to the Icom R71A IF filter selection circuit
Author: Greg Doerschler - gkd@wpi.edu.MODIFICATION.NET


This article may be distributed or reposted freely provided that it remains completely intact.

INTRODUCTION:

Simple modification to the IF filter selection circuit of the ICOM R71A general coverage receiver can provide additional bandwidth selection options in receivers which have been equipped with the optional FL-44A high grade 2.4 KHz crystal filter (or equivalent). In the AM mode, the modification enables a 2.8 KHz bandwidth to be selected in addition to the 6 KHz and 2.4 KHz bandwidth settings which the "FL-44A"-equipped R71A already offers. In the SSB, CW and RTTY modes, the modification can be used to enable the PBT knob to function as either a passband tuning control or an IF-shift control.

The potential benefit of this modification depends to a large extent on how the receiver is used. R71A owners considering the modification should take some time to decide whether it is worth the effort before proceeding. Much of this article discusses the rationale behind the modification and explains its actual effect. The procedure itself - described at the end of the article - is not very complex, but it does involve some delicate soldering and the ability to read schematic diagrams and identify components on the PC boards.

I can attest that my modified R71A performs as indicated, but I assume no responsibility for the outcome of anyone's modification efforts. Make sure you understand and are comfortable with what you are doing, and proceed at your own risk. While not absolutely critical in this case, it is generally smart to have a service manual handy when modifying equipment.

BACKGROUND:

Intermediate Frequency (IF) bandwidth filtering in the R71A is accomplished by filters in the 9 MHz 2nd IF stage and in the 455 KHz 3rd IF stage. The stock R71A comes with the following standard filters:
    2nd IF:  FL-70 (2.8 KHz)       3rd IF:  CFW455IT (6 KHz)
             FL-30 (2.3 KHz)                CFJ455K5 (2.8 KHz)
While the 2nd IF filters are of reasonable quality, the 3rd IF filters are inexpensive ceramic filters. ICOM offers the FL-44A 2.4 KHz high grade crystal filter as an optional replacement for the 2.8 KHz CFJ455K5. Other filter manufacturers have comparable replacements available too. One of two optional (additional) CW filters may also be installed in the 2nd IF; the FL-32 (500 Hz) or the FL-63 (250 Hz).

With only its stock filters, the R71A utilizes the following filter combination in its various modes:
                      2nd IF                  3rd IF
    AM wide...............(none)................ 6 KHz (CFW455IT)
    AM normal............ 2.8 KHz (FL-70)....... 2.8 KHz (CFJ455K5)
    SSB/CW/RTTY wide..... 2.8 KHz (FL-70)....... 6 KHz (CFW455IT)
    SSB/CW/RTTY normal... 2.3 KHz (FL-30)....... 2.8 KHz (CFJ455K5)
At first glance, one might think that it would have been more logical to use both 2.8 KHz filters in the SSB "wide" position (similar to the AM "normal" position), rather than a 2.8 KHz filter followed by a 6 KHz filter. (Since the narrower of the filters in the IF chain really determines the overall bandwidth, the 6 KHz filter is actually doing nothing.) However, if things had been set up this way, replacement of the 2.8 KHz 3rd IF filter with the optional FL-44A 2.4 KHz high grade crystal filter would have restricted the SSB "wide" bandwidth to 2.4 KHz. The SSB "wide" and "normal" bandwidths would then have been virtually identical.

Observe that the installation of the FL-44A does in fact reduce the AM "normal" bandwidth from 2.8 KHz to 2.4 KHz. Here's how the filter chart would look for an R71A with both the optional FL-44A and the optional FL-32 CW narrow filter installed:
                             2nd IF                 3rd IF
    AM wide.................. (none)................ 6 KHz (CFW455IT)
    AM normal................ 2.8 KHz (FL-70)....... 2.4 KHz (FL-44A)
    SSB/CW/RTTY wide......... 2.8 KHz (FL-70)....... 6 KHz (CFW455IT)
    SSB/CW/RTTY normal....... 2.3 KHz (FL-30)....... 2.4 KHz (FL-44A)
    Narrow-all modes......... 500 Hz  (FL-32)....... 2.4 KHz (FL-44A) 
Having the razor sharp 2.4 KHz bandwidth of the FL-44A accessible in the AM mode can sometimes be great for critical DXing, but AM audio at that bandwidth does lack sufficient fidelity for comfortable listening.

With some minor rewiring of the filter selection hardware, the 2.8 KHz AM bandwidth can be restored in "FL-44A"-equipped R71A receivers. This is done by making the AM "normal" setting select the same 2.8 KHz (FL-70) / 6 KHz (CFW455IT) filter pair which is used in the SSB "wide" setting. For experimental purposes, I had temporarily configured my R71 to select this filter pair in the AM "wide" setting in order to make direct receive fidelity and skirt selectivity comparisons against the 2.4 KHz AM "normal" setting.

My findings revealed that with the receiver tuned directly to a broadcast station, both bandwidths produced very similar sounding audio without much fidelity. But by tuning the R71A's main tuning dial 1.5 KHz away from the AM carrier frequency, the 2.8 KHz filter passed the carrier and enough of one of its sidebands to provide halfway decent fidelity. (It was noticeably less than the 6 KHz bandwidth, but still quite usable.) The same trick was also tried with the narrower, 2.4 KHz passband by tuning the main dial 1 KHz off frequency; but even then the fidelity was still too restricted for comfortable listening.

Since the 2.8 KHz bandwidth seemed to isolate noisy AM signals just as well as the 2.4 KHz setting in most of my tests, I had initially considered replacing the 2.4 KHz setting with 2.8 KHz in order to take advantage of the additional fidelity. However, I did encounter some relatively rare instances when trying to tune in a weak AM station adjacent to a strong local broadcaster where the 2.8 KHz/6 KHz filter pair allowed some odd residual noise from the strong adjacent signal to become embedded in the desired signal. The noise was not there when using the 2.8 KHz/2.4 KHz filter pair. This revelation led me instead to devise a way of making both bandwidths available in the AM mode (in addition to the 6 KHz bandwidth).

TECHNICAL DISCUSSION:

For the following technical discussion of the IF filter selection circuit of the R71, you may wish to refer to your schematic diagram or service manual. The filter select IC is IC3 on the main PC board. It has three input pins (pins 9, 10, and 11); the logic state of which are determined by the operating mode (AM, FM, SSB/CW/RTTY) and by the position of the "wide" and "narrow" filter switches on the front panel. The configuration of these settings determines which IC output pin goes high. (Output pins are pins 1, 2, 4, 5, 12, 14 and 15.) Diodes connected from the output pins to the various filters determine which filters are activated by each specific mode-bandwidth combination. There are two output pins (pins 1 and 4) which are only activated in the FM mode. These outputs are unused (not connected to anything) since the optional FM board has its own IF filter which is automatically selected in the FM mode.

The following table from the service manual shows the input-output relationship of IC-3:
                                 INPUT PIN
    MODE                        9   10   11    OUTPUT PIN

    SSB/CW/RTTY normal          L    L    H        14
    SSB/CW/RTTY wide            H    L    H         5**
    SSB/CW/RTTY narrow*         L    H    H        12
    AM normal                   L    H    L        15
    AM wide                     H    H    L         2
    AM narrow*                  L    H    H        12
    FM normal                   H    L    L         1
    FM wide                     H    L    L         1
    FM narrow*                  H    H    H         4

    *  assuming optional filter switch (S1 on main PC board) is ON.
    ** this output was incorrectly listed as pin 3 in the 
           service manual.
There are two wires which send logic data from the filter switches on the front panel to the IC input pins. One goes high when the "wide" button is depressed and the other goes high when the "narrow" button is depressed. The switches are deliberately interconnected in such a way that both wires are low when the switches are simultaneously depressed (just like if neither switch were depressed). By installing two solder bridges on the PC board where the switches are mounted, this interconnection can be defeated so that both wires will go high when the switches are simultaneously depressed. Doing this causes one of the unused "FM" output pins on the filter select IC (pin 4) to be activated in any mode. Installing diodes from this pin to the IF filters essentially provides an additional filter selection option.

I decided that my AM normal "both switches out" configuration would be the 2.8 KHz setting (2.8 KHz FL-70 and 6 KHz CFW455IT), and that the "both switches in" configuration would be the narrower setting employing the 2.4 KHz FL-44A in the 3rd IF. But rather than use the 2.8 KHz (FL-70) filter in the 2nd IF for this narrower setting, it made more sense to use the 2.3 KHz (FL-30) instead since the FL-30's bandwidth more closely matched that of the FL-44A.

There was another advantage to setting the options up this way. The "both switches in" bandwidth selection is the same in all reception modes. Since the FL-30/FL-44A combination was already the "normal" (both switches out) SSB/CW/RTTY selection, I had the opportunity to change that selection without losing access to the FL-30/FL-44A filter combination in the SSB/CW/RTTY modes.

By making the SSB/CW/RTTY "both switches out" setting use only the FL-44A in the 3rd IF (bypassing the 2nd IF filters altogether), the passband tuning control would act like an IF-shift control when this setting was selected. I found this option to be useful when tuning in AM broadcast stations in the SSB mode using ECSS reception. By adjusting the IF shift function so that the passband was centered directly over the AM carrier, the upper and lower sideband components could be heard beating against each other. The main tuning dial could then be adjusted until a "zero beat" was heard; indicating that the signal was properly tuned.

Note that since bypassing the 2nd IF filters does reduce the dynamic range of the receiver, use of the IF-shift function in the presence of very strong signals on nearby frequencies may impair reception (similar to what happens in the AM wide position).

With the above changes done, here's what my filter selection configuration would look like:
                                2nd IF                 3rd IF
AM, wide button in............. (none)................ 6 KHz (CFW455IT)
AM, both buttons out........... 2.8 KHz (FL-70)....... 6 KHz (CFW455IT)
SSB/CW/RTTY, wide button in.... 2.8 KHz (FL-70)....... 6 KHz (CFW455IT)
SSB/CW/RTTY, both buttons out.. (none)................ 2.4 KHz (FL-44A)
ALL MODES, both buttons in..... 2.3 KHz (FL-30)....... 2.4 KHz (FL-44A)
ALL MODES, narrow button in.... 500 Hz  (FL-32)....... 2.4 KHz (FL-44A)**

** This bandwidth is of no use in the AM mode, but there is no way to 
   change it without affecting the other modes as well.
The only negative consequence of these changes is that operation of the filter select switches is a bit more complex, but I found it became second nature very quickly.

PROCEDURE:

There are many possible ways that the filter selection circuit could potentially be modified. I will detail three options:
  1. Implement the modification exactly as I have described above.

  2. Implement the modification exactly as I have described above, except use the "narrow" filter switch rather than the "both switches in" configuration to access the extra bandwidth setting. This may only be done if no optional CW narrow filter has been installed.

  3. Replace the 2.4 KHz AM "normal" bandwidth with 2.8 KHz. Make no other changes to the filter select circuit.
These three options are listed in decreasing order of complexity. Options 1 and 2 produce identical results, except that different filter switch positions are utilized. Options 2 and 3 only require the top cover of the R71A to be removed. Option 1 requires that both the top and bottom covers be removed so that the front chassis can be partially removed to access the filter switch PC board. For option 1, you will need two small general purpose switching diodes. No additional components are required for options 2 and 3. A short length of thin flexible insulated wire will be needed to make a few small jumper connections.

PREPARATION:

Read the procedures and make sure you have all the necessary part and tools on hand. I suggest taking all appropriate anti-static precautions whenever working on radio gear. Be sure power is disconnected from the receiver. Use only a low wattage, fine point soldering iron. It is important to use as little heat as necessary for all solder connections on the top side of the main PC board to avoid melting the solder on the underside.

[Remember, these modifications will only be of potential benefit if the optional FL-44A crystal filter (or equivalent) has been installed. Some dealers also offer 4 KHz filters as replacements for the 6 KHz CFW455IT ceramic filter in the 3rd IF. Installation of these replacement filters should not have any effect on the results of the modifications.]


OPTION 1
CHANGES ARE IMPLEMENTED EXACTLY AS DISCUSSED IN THE PRECEDING TEXT:

  1. Remove the top and bottom covers. Place the receiver (top side facing up) on a stack of magazines or large books at least 2" thick. Only the metal chassis should rest on the stack, not the front panel.

  2. You will see two flathead screws on either side of the receiver which hold the front chassis assembly to the main chassis. Remove only the top screw on each side and loosen the lower ones slightly. Using the lower two screws as a hinge, carefully fold the front assembly down so that the face of the radio rests on the desk. (A soft cloth may be used to prevent scratches.)

  3. Right beneath the back of the S-meter, you will see a PC board to which the wide and narrow filter switches connect. Locate the 12 solder points in a straight row associated with the two switches. There is a slight gap between the switches which contains two additional solder points just above and below those in the line. (The board layout diagram supplied with the service manual is quite helpful in locating the appropriate solder points.) You need to create solder bridges across the outermost set of normally open/normally closed switch contacts for each of the two switches. The appropriate pins are shown below:
              wide switch         narrow switch       bottom of radio
                                                             ^
                              .                              |    XX=solder  
            .  .XX.  .  .  .     .  .  .  .XX.  .            |       bridge
                              .
    
  4. Inspect your work. Carefully return the front assembly to its proper position and secure the four flathead mounting screws. Re-install the bottom cover.

  5. Turn ON the filter switch (S1) on the main PC board. This switch will already be on if an optional CW narrow filter has been installed. S1 is a small slide switch not far from the center of the board.

  6. You may wish to verify that everything is working OK so far. If so, be sure that all tools, etc. are out of harm's way and reconnect power, antenna and an external speaker to the receiver. The bandwidth switches should work the same as before, except that (1) there will be no receive with both switches pushed in and (2) there will be no receive with the "narrow" switch pushed in unless an optional CW filter is installed. Disconnect power again once the tests are complete.

  7. Locate D37 on the main PC board right next to IC3 near the center of the board. Cut the top (cathode) lead of the diode, leaving enough wire on both sides of the cut to make connections to. Bend the wire lead on the diode up. Solder a jumper wire from the cathode lead of D37 to the cathode (top) lead of D39 (located on the opposite side of IC3).

  8. PERFORM THIS STEP ONLY IF YOU WISH TO MAKE THE "IF-SHIFT" MODIFICATION FOR THE SSB/CW/RTTY "BOTH SWITCHES OUT" POSITION, AS DISCUSSED IN THE PREVIOUS TEXT. IF YOU ONLY WANT THE EXTRA AM BANDWIDTH, SKIP TO STEP "I." Cut the top (cathode) lead of D44, leaving enough wire on both sides of the cut to make connections to. Bend the wire lead on the diode up and solder a jumper wire from it to the top (cathode) lead of D42 (located near filter switch S1).

  9. A switching diode must be connected from pin 4 of IC3 to the top (cathode) lead of D36 (located right next to D37). A second diode must be connected from pin 4 of IC3 to the lead sticking out of the PC board which was clipped from D44. If D44 was not clipped in step H, the diode just connects to top (cathode) lead of D44. To make the IC3 connection, tin both pin 4 and the lead which will connect to it; then place the two in contact with each other and heat up the connection.

    I performed this step by first soldering the anode of one of the switching diodes to the anode of the second; right where the lead enters its base. I then cut the anode lead of the first diode to a fairly short length and soldered it to pin 4 so that the two diodes were held in a vertical position just a tad above the IC. I then clipped the two cathode leads very short and ran insulated jumper wires from one cathode to D36 and from the other cathode to the D44 clipped lead coming out of the PC board. However you decide to do it, make sure the IC3 connection does not short out any other pins and make sure the switching diode leads cannot come in contact with any other components.

  10. Inspect your work and verify all steps were done properly. Make sure all tools are out of harm's way and test the modification. If everything works OK, reassemble the receiver. Note that with this modification, the narrow button must be in the "out" position for the FM unit (if installed) to function properly.


OPTION 2
CHANGES ARE IMPLEMENTED EXACTLY AS DISCUSSED IN THE PRECEDING TEXT EXCEPT THE "NARROW" FILTER SWITCH IS USED INSTEAD OF THE "BOTH SWITCHES IN" CONFIGURATION TO ACCESS THE ADDITIONAL BANDWIDTH. THIS OPTION MAY ONLY BE USED IF NO CW NARROW FILTER HAS BEEN INSTALLED IN THE RECEIVER.

  1. Remove the top cover of the receiver.

  2. Turn ON the filter switch (S1) on the main PC board. S1 is a small slide switch not far from the center of the board.

  3. Locate D37 on the main PC board right next to IC3 near the center of the board. Cut the top (cathode) lead of the diode, leaving enough wire on both sides of the cut to make connections to. Bend the wire lead on the diode up. Solder a jumper wire from the cathode lead of D37 to the cathode (top) lead of D39 (located on the opposite side of IC3).

  4. PERFORM THIS STEP ONLY IF YOU WISH TO MAKE THE "IF-SHIFT" MODIFICATION FOR THE SSB/CW/RTTY "BOTH SWITCHES OUT" POSITION, AS DISCUSSED IN THE PREVIOUS TEXT. IF YOU ONLY WANT THE EXTRA AM BANDWIDTH, SKIP TO STEP "E." Cut the top (cathode) lead of D44, leaving enough wire on both sides of the cut to make connections to. Bend the wire lead on the diode up and solder a jumper wire from it to the top (cathode) lead of D42 (located near filter switch S1).

  5. Cut the top (cathode) lead of D46 (located a little toward the front of the main PC board). Make sure the two clipped leads are not touching.

  6. Locate D45 on the main PC board (near IC3). Cut the top (cathode) lead of the diode, leaving enough wire on both sides of the cut to make connections to. Bend the wire lead on the diode up. Solder a jumper wire from the cathode lead of D45 to the lead sticking out of the PC board which was clipped from D44. If step D was not performed, then solder the jumper to the cathode (top) lead of D44.

  7. Inspect your work and verify all steps were done properly. Make sure all tools are out of harm's way. Reconnect power, antenna and an external speaker, and test the modification. You should now have the following bandwidth settings:
        AM wide................ 6 KHz    (CFW455IT)   [no change]
        AM normal.............. 2.8 KHz  (FL-70/CFW455IT) 
        SSB/CW/RTTY wide....... 2.8 KHz  (FL-70/CFW455IT)  [no change]
        SSB/CW/RTTY normal..... 2.4 KHz  (FL-44A) [IF-shift, if step D was 
            or                                    performed]
        SSB/CW/RTTY normal..... 2.3 KHz  (FL-30/FL-44A) [no change, if step D
                                                  was not performed]
        Narrow, all modes...... 2.3 KHz  (FL-30/FL-44A)
    
    If everything works OK. reassemble the receiver.


OPTION 3
REPLACE THE 2.4 KHz AM "NORMAL" BANDWIDTH WITH 2.8 KHz. MAKE NO OTHER CHANGES TO THE FILTER SELECT CIRCUIT.

  1. Remove the top cover of the receiver.

  2. Locate D37 on the main PC board right next to IC3 near the center of the board. Cut the top (cathode) lead of the diode, leaving enough wire on both sides of the cut to make connections to. Bend the wire lead on the diode up. Solder a jumper wire from the cathode lead of D37 to the cathode (top) lead of D39 (located on the opposite side of IC3).

  3. Inspect your work and verify it was done properly. Make sure all tools are out of harm's way. Reconnect power, antenna and an external speaker and test the modification. Your AM "normal" bandwidth will now be 2.8 KHz (FL-70/CFW455IT) instead of 2.4 KHz (FL-70/FL-44A) If everything works OK, reassemble the receiver.

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19-07-1998 add a comment
Here is the R-71 version of the Drake R7/R8 type passband tuning system

Add a jumper wire between the cathodes of diodes D42 and D45 on the main unit circuit board. The cathode end of the diode is marked by a band. The diodes are located near Filter Switch 1 (the switch you set when you add the optional narrow filter). Turn Filter Switch 1 on. That's it.

Usage: select LSB mode and narrow filter position, and tune to zero-beat. Rotate the pass-band tuning control to select between LSB and USB, or anywhere in-between. Select normal or wide filter position and you get the original ICOM PBT.

The mod for the R70 should be just as easy, but you'll have to find the diodes on your schematic. Just jumper the cathode of the diode that selects the optional narrow 2nd IF filter to the cathode of the diode that selects the "through" postion in the 2nd IF.

This modification will bypass any narrow filter you may have installed. It forces the narrow filter selection to bypass the 2nd IF filters, while still selecting the narrow filter in the 3rd IF. The standard ICOM pass-band tuning shifts the 3rd IF passband against the 2nd IF passband:
            No PBT shift           LSB shifted              USB shifted
              __|__                    __|__                    __|__      
 2nd IF      /  |                    /  |                    /  |       
            /   |                   /   |                   /   |       
        ___/    |    \___        ___/    |    \___        ___/    |    \___
              __|__                  ____|                        |____    
 
 3rd IF      /  |                  /    |                      /|       
 
            /   |                 /     |                     / |       
 
        ___/    |    \___        _/      |  \_____        _____/  |      \_
              __|__                    __|                        |__      
result       /  |                    /  |                      /|       
            /   |                   /   |                     / |       

        ___/    |    \___         __/    |  \_____        _____/  |    \___
                |                        |                        |        
             ^     ^                  ^   ^                      ^   ^     
 
            full b/w                narrowed b/w             narrowed b/w 
This mod bypasses the 2nd IF filter, so you have just the 3rd IF filter, which the PBT control can move around relative to the center frequency:
            No PBT shift           LSB shifted              USB shifted
              __|__                  ____|                        |____
 
 3rd IF      /  |                  /    |                      /|    
  
            /   |                 /     |                     / |       
 
        ___/    |    \___        _/      |  \_____        _____/  |      \_
                |                        |                        |        
             ^     ^                ^     ^                      ^     ^   
   
            full b/w                shifted b/w               shifted b/w 
I haven't performed this mod on my R71 (I have to install PBT tuning first - I got one of the ones without PBT), so you're on your own with this one. I expect that the close-in dynamic range will be worse when using this flavor of PBT on the R71, since the 2nd IF filter is bypassed

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23-08-1998 add a comment
R-71A Memory Notes

I have heard that a new company named Willco is going to sell no fail memory for the Icom radios.

Two models, one with 64 channels for around $70 and a 1000 memory channels for around $149 will replace the small battery backup unit. The Willco board will use standard AA batteries. When the batteries die in the Willco unit, the radio won't fail and need servicing as is now the case. (However, the memories would need to be re-programmed.)

Using the lock button and memory switch, one steps through the banks of 32 channels each. One channel in each bank can be used to store the channel number for display to identify the bank number according to the maker.

Willco's address is P.O. box 788 NewLenox Il. 60451

If someone orders one, let me know what you think of it. I am not sure which radios other than the R-71A in which it will work.
David L. Wilson             dwilson@s850.mwc.edu
Department of Mathematics   Phone: H (703)898-1084  W (703)899-4744
Mary Washington College     Amateur callsign:  AC4IU (ex-KD4ASW/KO4EQ)
Fredericksburg, VA  22401   Lat./Long.:  38 15 40 N/ 77 32 51 W

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30-03-2001 add a comment
RAM Card Backup Battery Replacement Instructions
Author: ICOM


In the early 1980s Icom America marketed a group of transceivers and radios that utilized the latest state-of-the-art computer technology to enhance the operation of the radios. This technology improvement allowed hams to afford a reasonably priced high performance transceiver which until then was only available on units costing much more. Features now available to the hams included: higher frequency stability, better frequency resolution, digital frequency display, almost instant recall of saved frequencies (memory channels), quick mode signal processing and built in tones and offsets for the rapidly emerging repeater operation.

Implementation of all these features required a CPU with associated logic circuitry. In the early 80s, the most cost effective way to implement data processing and memory functions was through a DRAM (Dynamic Random Access Memory) to control the CPU. This DRAM was a volatile memory integrated circuit which required a lithium battery to retain its instruction set. The following receivers and transceivers had such RAM units:

IC-271 ; IC-471 ; IC-1271 ; IC-745 ; IC-751/A ; IC-R71A

The lithium batteries in these units typically lasted about 5 to 7 years before replacement was required. This was specifically noted in each of the Owners Manuals for the products.

This lithium battery can be replaced by the radio owner if care is used. The following is a recommended procedure to accomplish this:

Procedure

  1. Disconnect the power cable from the radio, and take the cover off.

  2. Unplug the RAM board and remove it from the radio.

  3. Temporarily solder a 3 Volt DC battery source across the existing battery terminals (see suggested connection points on the circuit board pictures).

  4. Unsolder the old lithium battery and replace it with a new one. (BR2325 1HC, ICOM stock number 945 03112)

  5. Unsolder your temporary 3 Volt DC source.

  6. Reinstall the RAM board into the radio.

Cautions

  1. Do not use an AC powered 3 Volt DC source, your grounded soldering iron tip could short out the battery (+) terminal. Use a 3 Volt battery DC source only (2 alkaline cells for example).

  2. Do not solder the external DC wires directly to the lithium battery tab pads. If you do so, you will not be able unsolder the battery without having the wires drop off.

  3. If by accident you lose power to the RAM unit it must be sent to Icom America for reprogramming.

  4. Be careful not to damage or bend the connector pins on the radio side while removing or reinstalling the RAM card.

Pictures

There are two versions of the ICOM RAM boards. Both are identical in operation, and they are interchangeable. The differences are in the circuit board layouts only. Note that the black and red wires visible on these images are the suggested way of connecting the external DC backup voltage while the battery is being replaced. The wires are not a part of the RAM card, and should be removed when the battery replacement procedure is complete. Refer to the replacement procedure outlined above.

RAM card version A images:


RAM card version B images:

This modification can also be found at ICOM's own homepage on the following URL: "RAM Card Backup Battery Replacement Instructions"

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18-11-2001 add a comment
RAM board programming interface & R71A modification

11 December 1999 by Andrew Gerald, N2CBU

eMail-1: Lorand@QwestInternet.net
eMail-2: N2CBU@ARRL.NET

A word of caution before you begin:

It's possible that due to a wiring error, parallel port error or software incompatibility you might erase the contents of your RAM module. If your RAM module is from an R71A you can restore its contents from the enclosed "ORIG-R71.BIN" file. I do not have any other "recovery" files and until some become available I urge caution. Perhaps it would be wise to test your interface on a RAM module from a R71A first before reading RAM modules from other radios. I will add "recovery" files for the other radios to this archive if they are sent to me.

*** Note-1: If the "WP" Write-Protect pin (see J2 on the interface schematic) is tied to ground instead of to +5v the critical lower RAM locations in the module are write protected. A simple modification to the interface board would be to add a write protect switch.

*** Note-2: If the "/WR" Write pin (see J2 on the interface schematic) is left unconnected when testing the interface then the entire RAM will be write protected. Thus you can test without much chance of erasing the contents of the RAM module.

Icom RAM board programming interface & R71A modification notes

You will need a CD4040 IC, a 78L05 voltage regulator, an 8-pin strip of 1" tall 0.1" spaced header pins, a 12-pin strip of 1" tall 0.1" spaced header pins, a DB25M, a length of ribbon or other type cable, and a piece of perf board. For the prototype I used a Radio Shack part number 276-149 prototyping board. It should be noted that my prototype does not have an on-board voltage regulator. I included the regulator on a subsequent board I built in 1991 which I gave away.

All parts may be obtained from Digikey (www.digikey.com) and certainly from other sources. A suitable header pin strip is Digikey part number "S1081-36" but any similar header pin material will work.

Circuit layout is simple, just take a look at the ram module in the R71 and imagine how the header material will have to be positioned. What you want to do is make a "socket" on the programming adapter which looks just like the "socket" in the R71A. Build up the circuit on a small piece of perf board with the 4040 in the center. The long side of the header pins will have to be bent slightly outwards for the ram module to fit. The ribbon cable from the PC will attach near the smaller header strip.

For the R71A to tune above 31 MHz, in addition to editing the RAM module, you will have to make a modification to the Logic Unit. I have included a file which describes how to do this. See the file named "R71MEM.TXT" for instructions. Credit for this part of the mod goes to the author of that file.

The software is NOT a polished product. There isn't much in the way of error checking when reading or writing a file to disk. It will however verify writes to the RAM module automatically after writing. I just added an unlisted (V)erify function accessable from the menu and an automatic CPU timing test. The software should work with a standard IBM-PC bi-directional parallel port with base addresses of 3BC, 378 and 278. Most modern computers, including laptops, now have bi-directional parallel ports. You may however need to mess with your parallel port configuration. I have not had any trouble running the software on my IBM Thinkpad 486-25 or on my AMD-K6-III-450 tower. That doesn't mean it will work for everyone though. Bi-directional mode is selected by writing a "one" bit to port base+2.5 and if your port works differently the program will likely fail. I have heard that some of the more advanced parallel port ICs need to have an "unlock" bit set before bi-directional mode can be enabled. If anyone can provide me with the necessary info I will update the software to support these ICs.

Note that values stored in the RAM module are big-endian and that the static RAM IC is only 4-bits wide (nibble mode.) Some important memory addresses (in hex) in the RAM module for the R71A are as follows:

10/11 = LSB offset
12/13 = USB offset
14/15 = AM offset
16/17 = CW offset
18/19 = RTTY offset
(FM has no offset)

30/31 = lowest frequency (factory is 100kHz)
3B/3C = highest frequency (factory 30MHz)

Example 1 - To change the lower frequency limit to 10kHz:

Original - 000: 00F1FF1FF002FFFF000B59686800032005930005000000000100000030003000
Modified - 000: 00F1FF1FF002FFFF000B59686800032005930005000000001000000030003000

Example 2 - To change the upper frequency limit to 35MHz:

Original - 000: 00F1FF1FF002FFFF000B59686800032005930005000000000100000030003000
Modified - 000: 00F1FF1FF002FFFF000B59686800032005930005000000000100000030053000

I have enclosed the file from my R71A receivers (MY-R71.BIN and the hex dump MY-R71.HEX) as a starting point for offset tweakers. The offsets are big-endian meaning that the first value is the least significant. You can compare these files against the non-tweaked files (ORIG-R71.BIN and the hex dump ORIG-R71.HEX) to see what changes have been made.

Download the whole file.

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