4. Program the radio to the local weather channel (162.400 or 162.550) in the following manner: 0 or 0 NOTE: the programming proceedure now requires that you enter the ten's of Mhz when entering a frequency. 5. Look at the back of the radio. In approximately the center of the exposed board is a metal can with two adjustments. The top adjustment is a metal screw (actually a trimmer capacitor) while the bottom adjustment is a black slug with a small rectangular adjusting slot 6. With the squelch open, adjust the lower black core counterclockwise approximately 1 1/4 turns until you receive the weather station. As soon as you receive the weather, STOP turning the adjustment. 7. Replace the back on the radio and you are in business. With this modification, the radio will tune from 140.000 Mhz to something over 162.550 without difficulty. Just remember that you must enter the ten's of Mhz when entering a frequency. This modification does not affect the transmitter which still covers 140.000 to 151.995 Mhz. Please note: This mod does not retune any of the RF stages of the receiver so the sensitivity is down some at the weather frequency, however, I have no difficulty receiving it at thirty to forty miles. I do have the ICOM service manual on the IC-02A. I purchased it from Delaware Amateur Supply at a local hamfest several weeks ago. According to the manual, the VCO on the PLL should cover 25 Mhz. minimum.
This modification is read 1203 times.
(IC-02) Low audio speaker mike on IC2A, 3A, 4A OR 02AT
If you own one of the IC2A, 3A, or O2AT series Hand-helds, you may be interested in reading on. I know my hearing is pretty good, but have you ever tried to listen to the audio coming out of your speaker mike on the above ICOM's? For the most part, it's pretty low. I may be the last guy to figure out a cure for this, but here it is anyway. On the O2AT, etc., there is a groove on the back near the top of the rig that is just the right size to accept the HM9 speaker mike turned 90 degrees so that the mike plug fits in that groove in the rear of the rig. Thus alllowing all the audio to be heard from the internal speaker of the rig, usually much better than the speaker mike. Now, in the case of the 2A series, etc., the fix is more complex. These rigs don't have that handy groove built in, so I decided a groove had to be made to accept this configuration. I thought long and hard about a minute, before getting the "Dremel" out and making my own slot or groove. It works well on both hand-helds I have. In fact, you can hook up an external speaker for even more loudness in the auto. So, give it a try or see me for a demo.

This modification is read 739 times.
(IC-22) Recieve SSB and CW on IC-22S
Would you like to convert your IC-22S to receive SSB and CW signals? If you own a shortwave receiver, or a general-coverage HF rig, you can do it easily, for less than a dollar! All you need to do is to take a sample of the 455 KHz IF amplifier signal in your IC-22S and apply it to your shortwave receiver, tuned on 455 KHz in USB, LSB or CW. Connect a 68 K ohms resistor on the collector of Q6 (455 KHz IF amplifier). It's a 455 KHz IF amplifier, NPN 2SC945; collector is the center pin. Connect the free end of this resistor on the inner conductor of a coaxial cable. Connect the shield of this coaxial cable on the ground (-) of the IC-22S. The other end of this coax is connected on the antenna connector of your shortwave receiver, with the appropriate connector. This coax could be RG-58U or shielded speaker wire; the length is according to your convenience. The resistor is used to limit loading of the IF amplifier. The frequency you want to listen is selected on the IC-22S. Your SW receiver must be tuned on 455 KHz. The mode you want to use (USB, LSB, CW) is selected on your SW receiver. This modification can NOT be done in transmission, because too many modifications of the IC-22S are involved. You would need to change the RF amplifier because it's in class C, which doesn't work in AM and SSB. R149 pot: adjusts low power. Reducing R148 increases maximum low power (less than 10 Watts.) possible with R149 pot. R73 pot (30K): adjusts TX meter readout. When this pot is connected on D10 instead of D11, the meter indicates SWR. R73 could therefore be used to calibrate FORWARD reading. R89 pot (100K): Adjusts SWR feedback, and therefore SWR protection level. R132 pot: adjusts Mic. Gain. R124 & R112 pots: Adjusts Maximun deviation. R124 pot: Adjusts symmetry of clipping of mic. amplifier.
This modification is read 726 times.
(IC-22) Modifying the IC22A for 9600 baud operation
Author: Mike Curtis by Mike Curtis, wd6ehr and Dave Shalita, w6mik This is one of the more difficult rigs to modify - most are even simpler! This mod will make your IC22A into a dedicated 9600 baud packet radio. Components with * are added to the crystal board. Remove the trimmer capacitor for the transmit crystal socket you'll be using for 9600 baud. Replace with the above circuit. The 420 pF trimcap should be a good quality ceramic or other low-drift trimmer. (Sorry - Radio Shack doesn't have anything suitable.) Connect 2 10K resistors to C-53 (both sides) and tie the other ends together. This junction is where you'll pick off your RXA. Turn R-67 (dev control next to P-1 and P-2) completely counterclockwise. This kills signals that may get into the phase modulator. Using a service monitor, or oscilloscope connected to the detector of a receiver, adjust the varactor bias for the best eye pattern. Alternate bias adjustment: Use the k9ng's 4800 Hz "idle" tone to adjust your modulator for best linearity. Using a service monitor, or a receiver with a fairly wide passband, adjust varactor bias for the "best" sine wave. Thanks to Brian Kantor wb6cyt for this tip.

_________________________________________________________ R5 R4 | R1 | R2. D1 D2 -----------+. | -D3| -D4IC4 | -D5-----------+ -D6-D7. _ _ D8 D9 _ _ O. C7 ?x? X1 | ________________________________________________________|
So long, 73 from Brazil Marcelo Medrado ZZ2MWL
This modification is read 260 times.
(IC-2330) IC2330A expanded range
I picked up a IC-2330a and found there were no mods.at least i couldn't find any, so i decided to find them myself! and this is what i found. I have had no problems since performing these mods, but of course i claim no responsibility if you trash your radio, and of course it will void your warranty! OK here we go. on the logic board (behind the display board) are two diodes D5, and D6. cut D5 to get 215.00 to 230.00 Mhz TX/RX cut D6 to get 118.0 - 135.0 AM/RX There is a solder pad on the back of the logic board which when the pads are connected together will enable 136-174 TX/RX, but disable the tone encoder on 2meters only. haven't spent much time on that to figure out why or how to fix that so i left then unconnected (don't need to xmit there anyway) but if someone else can figure it out let me know! i love all mods so if anyone has any more they know of for this radio pass them along to me as well. Good luck and thanks for reading!! Steve KD6QPQ
This modification is read 628 times.

28-05-2000

(IC-2330) IC-2330A expanded range (another way)
Author: Takeshi Kudoh - takeshikudoh@usa.net.MODIFICATION.NET I found another way of modification for IC-2330. After the modification, we can receive;
118.000-135.995MHz 136.000-174.000MHz 144.000-146.000MHz 320.000-479.000MHz 430.000-440.000MHz 830.000-950.000MHz AM(RX) FM(RX) FM(TRX) FM(RX) FM(TRX) FM(RX)
This way might be more difficult than yours, but it is easy. First, a switching diode should be put on the circuit board in the circle on this picture. Second, the transceiver should be reset. To be reset, turn it on with pushing [SET]+[MW]. And turn off and turn it on again with [V/M]+[SET]+[DN]. [DN] key is located on microphone. That's all of modifications for IC-2330.
In addition, if you want to put an external antenna for 830-950MHz, put coaxial cable in the circle on this picture. This mods is shown in a web page in Japan. That means it wouldn't work well coz this mod is for IC-2330 sold in Japan.
Please try to do it and let me know the result. Regards//Takeshi Kudoh takeshikudoh@usa.net.MODIFICATION.NET
This modification is read 604 times.
(IC-2340) IC2340H att modification
From: 4z4zq@pc.4z7aba.ampr.ORG (Pinchook Ronen) This text deals with ICOM's Mobile radio IC2340H. On some of icom dual band mobile transceivers there is an RF attenuator which attenuates the received signal by 20dB. In my opinion this is a great feature especially when you operate in cities or in area's with lot of RF signals, repeater, etc. The attenuator function reduce the intermodulations that appears while receiving in those areas, and let you listen more quietly on your favorite channel, when you listen to a local repeater you can hardly feel the 20dB attenuator, but the intermodulations almost disappear. The problem is that the attenuator was featured on old icom mobile rigs (such as IC2340H, IC3230H), but not on the IC2340H. The next lines will guide you how to add this feature. All you need is 2 1p2t small switch, and 2 12Kohms resistors. VHF MODIFICATION 1. Open the upper cover of the transceiver. 2. Locate D9 on the print (left to the Power Amplifier while looking from the front of the transceiver) 3. Solder a 12K resistor to the anode of D9 as close as possible to the diode, (with no wire, the pin of the resistor should be soldered to the pin of the diode)

This modification is read 709 times.
(IC-2410) IC-2410 Modification area as follows. New and old version
For OLD version 1. Turn on the radio wtih pressing [V/MHz] + [SET] + [DN]on microphone. That's All!!! X-band reperter modification Cut diode [D2] on back side of front panel. Press [BAND] + [SET] more than 1 sec. cancel => press [SET] more than 1 Sec. For NEW version 1. 2. 3. 4. SEE THE BACK SIDE OF FRONT PANEL. YOU CAN FIND Li BATTERY. CUT [W27] or [D10] & [D8] Reset the radio.
After modification , you can recieve 118 - 135.995MHz AM 136 - 174MHz 320 - 479MHz 830 - 950MHz But 830 - 950MHz , you need to add ant for this band. open the lower panel , you can find [J2] ant connector.
This modification is read 717 times.
(IC-2410) IC-2410 TX modification
Both bands Replace the one sided D-14 on the logic board with a 1SS181 two sided diode, and short the solder tabs (position W3) which are directly below the location for D-14. Result: 136-174 Mhz tx 400-479 Mhz tx
This modification is read 764 times.
(IC-2500) Run 9k6 with an Icom IC-2500 (70cm/23cm TRX)
Yes it's possible to run 9k6 with an Icom IC-2500 (70cm/23cm TRX). I BELIEVE the 2m/70cm version (IC-2400) is similar to modify (Hopefully!) Here's my little description: RX: Pin 1 (=MDET) on the DET SW-Unit (mainboard A) Note: You receive on this Pin signals of that band, witch ist selected in the main display TX: You can take the Signal from R73, R72 or C137 Note: as written above
Comment: These TRX is accorded to my experiences relatively good qualified for 9600 Baud Packet-Radio Signals.
This modification is read 550 times.

28-03-1999

(IC-2500) Umbau des ICOM IC-2500E auf 9600 Baud
1. RX: NF an Punkt 1 (MDET) der DET SW-Unit auf Mainboard A abgreifen und z.B. auf Punkt 8 der Mikofonbuchse fuehren. Vorher LSLeitung von Punkt 8 entfernen. Es steht dann sowohl 70cm als auch 23cm vom Diskriminator zur Verfuegung. Punkt 8 der Mike-Buchse geht dann auf NFRX am TNC. (Evtl 10 Ohm Widerstand im TNC entfernen!!) 2. TX: Verbindungspunkt R73 (Hub 70cm),R72 (Hub 23cm) und C137 auf dem Mainboard A mit Punkt 4 ( NC ) der Mike-Buchse verbinden! (Leicht zugaenglich nach abschrauben und umklappen des Bedienkopfs) Punkt 4 dann mit NFTX vom TNC ueber einen 10uf-Elko verbinden. Mit einem Scope Tonrufamplitude an o.g. Verbindungspunkt messen. Dann Datensignal vom TNC auf etwa gleiche Amplitude einstellen! Das wars auch schon! Dies ist zwar eine Simpelloesung - lauft aber hier hervorragend! Fragen bitte an DL2GA @ DB0AAB! Viel Erfolg dann mit 9600!

This modification is read 3664 times.
(IC-706) Icom IC-706 Review
29 Dec 1995 From: randall@informix.com (Randall Rhea) ICOM IC-706 HF/VHF AMATEUR RADIO TRANSCEIVER Product Review, Hints and Tips, and Modifications As Of: December 28, 1995 by Randall Rhea, KG0HW Overall impression "Too good to be true". This was my understandable reaction to Icom's announcement of the IC-706 amateur radio transceiver last summer. It looked like my dream mobile rig: very small size, detachable face plate, all HF bands, FSK, 6 meters with 100 watts. AND 2 meters, all in one rig? It sounds too good to be true, but after using this radio in my car for about a month, I can tell you that this radio is real. Although the rig is not without its faults, Icom has produced an innovative masterpiece. The rig does just about everything as advertised. It is an easy-to-use radio that replaces several other radios that I was operating in my car. Over the Christmas holidays, I took a couple of long car trips here in Texas. The 706 was installed under a car seat, leaving plenty of room for luggage and packages. (Do NOT block the top of the rig. Leave room for air circulation. The rig gets VERY hot when transmitting!) The face plate was installed just below the dash within easy sight when driving. I used headphones, so my wife and daughter could listen to CDs while I was working DX. The headphone plugged into the face plate. I used a 7-foot whip mounted on the trunk of the car tuned for the SSB portion of 6 meters, my favorite band. The radio was a pleasure to use, even while driving. During a nice opening on 6 meters on the evening of December 27, I worked several new grid squares in the midwest and Arizona. I also worked North Dakota for the first time. I was able to work a station in Mexico City quite easily, despite the pileup. That 100 watts sure helps. (I previously used a 10-watt rig.) The sensitivity of the receiver, although not quite what the "pros" would want, was quite adequate. Noise from the car engine was only a minor problem; the noise blanker was effective for SSB. During the trip I also listened to a football game on TV channel 2, listened to truckers' traffic reports on CB channel 19 (27.185 MHz), worked a couple of 10m stations during the sporadic E opening on December 27, worked a couple of 20m stations, listened to WWV on 2.5, 5, and 10 MHz, eavesdropped on some interesting baby monitors and cordless phones on 49 MHz, listened to NOAA weather forecasts on 162.55 MHz, monitored some aircraft traffic, and did some ragchewing on 2-meter repeaters. Not bad for ONE radio! PRICE I paid $1249 for mine at Tucker Electronics in Dallas. They told me that they have sold about 200 of them in six weeks, making the IC- 706 their best selling rig of all time. They are getting them from Icom in lots of 20 and are having trouble keeping them in stock. Prices for accessories are pretty high. There is little profit margin in the box, so they make up for it with high accessory prices. The cable to allow for front-panel detachment is $48. UNIQUE FEATURES AND INNOVATIONS See www.icomamerica.com/icom/amateur/hf/#IC-706 for a list of features.

Delete cap. CT14 at pin 6 of IC3 on I.F. Unit. Rearrange the R9V to TR Q22 on I.F. Unit so that it is connected to unswitched "9volts supply. Do a similar mod. To the "9 volt supply to the A.F. unit to overcome surge pulse. Good luck de " RON " GM3SAE By PA3AXO Connections to acc. Jack on the back of the tansceiver: Pin Pin Pin Pin Keyline (note that 200 mA current capability is required so a dil relay may give problems) af to convertor FSK input TTL level ground
On main board: Remove C40/42/43/54 and replace by 0.1 uF Replace C69 by 10 nF On RF board: Remove C169 and 127 and replace C165 by 0.68 uF when desired the relay to control an external linear amp can be disconnected to reduce the clicking noises Good luck and best 73 de Jack PA3AXO
This modification is read 961 times.
(IC-725) ICOM IC-725 MARS modifications
DISCLAIMER: This modification allows the radio to transmit outside of the designated Amateur freq. Transmitting where you are not licensed to do so is unlawful! Disassemble radio following instructions on page 24 of Instruction manual, steps 1 - 7, or as follows: NOTE: All instructions with the radio's front panel facing you unless otherwise specified! 1. Remove all black screws from top & bottom covers and remove both covers. 2. Remove the 2 flat head screws that hold the PA unit to the front unit. (top front of radio - Not the screws that are in the plastic front panel.) 3. Remove the 2 screws that hold the PA unit to the rear panel. (Looking at the rear of the radio, 1 is above the ext. speaker jack & 1 is above to ACC(1) jack.) 4. Unplug the 2 plugs from J11 & J12. 5. D 6. Disconnect the large black connector on the left side of radio. 7. Slide up and out, the TUNER CONTROL SOCKET from it's holder in the rear panel. 8. Remove the tape from the right side of the PA unit. 9. Swing the PA unit up to the left and lay over flat. located to the left side, rear of the board, next to J4. You may have to remove J4 to allow access to D-5. 10. Reassembly is As if you were opening a book! You now have the PLL unit exposed. 11. Cut Diode D-5 from the PLL unit. D-5 is loca reverse of above. 12. The radio will now transmit from 1.5 MHz to 33 Mhz. (It will transmit even lower but the power output drops off and I don't know if doing so will damage the transmitter. ENABLE PREAMP Bve bottom cover. 1. Locate Q12 on Main Unit. 1/3 way from left side of board. Q12 is the transistor that bypasses the preamp below 1.5 MHz to avoid overload when listening to AM Broadcast Stations. 2. Clip the lead of Q12 closest the front of the radio. That's it, the preamp will now work below 1.5 MHz! ENABLE NOISE BLANKER IN ALL MODES

This modification is read 518 times.
(IC-740) Display/distortion problems ICOM IC-740 HF rig
Also probably would apply to IC 735 and IC 745 as well. The symptoms were distortion on transmit, a very unstable display, often tuning dial would not move frequency, display would give all kinds of random numbers, sometimes no numbers at all on sections of display readout. This appeared to be a mechanical problem, as a sharp "rap" on the case would change things, sometimes curing it temporarily. We pulled off the covers of the set, and gently tapped each board. The PLL board appeared to be the culprit. This is the small covered board to the rear left on the underside of the 740. We popped off the little cover over the board, loosened the 4 mounting screws and took out the board. Everything looked good, but the points on the board that contacted the metal standoffs were corroded and dirty. We flowed fresh solder around the screw holes on the board (underside), cleaned the standoffs and cleaned the chassis where they connected to it. This cured the problem. Interestingly enough, we did the same fix to an Icom 22S 2 mtr rig several years ago that would keep going out of "lock". It cured that problem as well. The bottom line is, make sure all your board to ground/chassis connections are real clean. Just a thin film of crud can cause all kinds of problems on a unit that uses the mounting screws as the ground return. Sometimes (but not always!) just loosening and retightening the mounting screws will help the problem.
This modification is read 503 times.
(IC-745) IC-745 - PROBLEM: Tuning counts slowly down
I have a problem with my 745. When I rang Bellevue, WA, they said: Never heard of it. My friend in LA who has the same pronlem got the same anser. The problem is as follows: The tuning counts slowly DOWN whether it's memory or VFO. I temporarily used the set by turning the dial in the UP direction faster than the countdown and then used the lock button when the set arrived on the desired frequency. The XIT?RIT can be used for small corrections. My friend who has a complete professional lab at his disposal found a temporary fix. He grounded pin 40 of the I/O IC which steers the CPU. Everything workds fine except that you miss the slowest tuning speed and that the UP/DOWN button on the mic does not work. I did the same and my set work the same. The tuning is a little bit coarse now but usable except you have to be careful especially with RTTY or AMTOR. The local ICOM repair shop is too busy at the moment with their normal work, and I don't like to be without this set for too ong a time. I can't use the 730 to drive my linear at least not without a lot of trouble. I suspect thqt one of the two transisstors has gone but which? I just wonder if any of your readers has had the same problem and fixed it. (ED Note: Anyone have the solution?) (Thanks, Bob Bartelings, VE6CBN, 170 Haysboro Crescent, Calgary, Alberta Canada T2V 3G3)

PA3HGT@ON1CED.WVL.BEL.EU

Here is two pictures from astra.
Here is anothe two photo from kb1vi

Date: 23-02-2002

From: Greg/K6QPV San Diego, CA. USA
Subject: Making 756P continuous Xmit 1.6 - 29.999 MHz Mods desired to use 756P as Xverter on 24 MHz which is out of its stock Tx range. I followed the suggested steps for making 756P continuous Xmit from 1.6 - 29.999. Bottom cover removed by 10 screws (6 on bottom and 4 on sides), no need to remove feet. CPU box is connected to mother board via two multi-conductor connectors. Easy to gently "rock" it back and forth, pops right off. Diodes on my Ver #2 were instantly identifiable. Heated one end, used very small blade knife to lift desoldered end. Left diodes connected and "hanging" by other end. Total time required approx 10 minutes. Piece of cake. No observable reduction in operation upon firing it up.
This modification is read 3371 times.

10-02-2002

(IC-756PRO) ICOM IC-756PRO CW Filter Shape Selection
Author: Greg Ordy - ordy@seed-solutions.com.MODIFICATION.NET

by Greg Ordy

Introduction The Undocumented BPF Indicator Two Ways to Specify the Filter Width Do It Yourself The Difference

Introduction

The ICOM 756PRO documentation is silent when it comes to describing the CW filter shape factor, and how it can be selected. ICOM tried to improve the situation with a brief mention of this topic in its Advanced Operation Guide for the 756PRO, but it does not clearly describe how to select the filter shape. I will try to do a little better on this page. I would like to thank Rob Peebles, W8LX, for bringing these capabilities of the radio to my attention. The 756PRO receive audio, coming out of a digital signal processing (DSP) intermediate frequency (IF) stage, is much different in character than other purely analog receivers. I have captured some of my impressions on another page. On CW, the filter response created by the DSP is extremely sharp. That is, signals outside of the passband are substantially attenuated. In the analog domain, sharp filters can lead to ringing, and other artifacts. Digital filters can have similar problems. In addition, it has been claimed that the 756PRO receiver highlights flaws (key clicks) in the transmitted signal. In other words, it hears the clicks better than other receivers. These various factors lead to CW receiver performance which some operators do not like. One suggestion to improve performance has been to alter the CW filter shape. Perhaps if the filter was not as sharp, the artifacts would not be as pronounced. Apparently a special DSP ROM (software) is available in Japan, but information on this modification has been difficult to obtain, and in any case, changing the DSP software is claimed to be a major project, in terms of taking apart the radio to access the relevant parts. It turns out that for filter widths of 500 Hz and less, it is possible to select one of two filter shape factors. One is the sharp CW filter, and the other appears to be the SSB shape factor, which is not as sharp. Calling one the CW shape factor and the other the SSB shape factor is my own terminology. Rob Peebles, W8LX, estimated the sharp CW shape factor to be 1.5, and the SSB shape factor to be 2.0. This page describes how to select the two different shape factors (in the CW mode, it cannot be selected in SSB mode).

Author: SM4RNA Anders - sm4rna@telia.com.MODIFICATION.NET At the input at the bandpassfilter on RF-Unit for MW, 0.5 to 1.6MHz, a 10dB attenuator is located. This attenuator also is a current limiter for the diode D19. By removing the attenuators three resistors and lead the diode current thru a inductor instead, the increased sensitivity is achieved. But important is to limit the current by changing the value on R119. To do the mod: 1. R116 is exchanged with an inductor of 1mH. 2. R117 removed and shorted. 3. R118 is removed. 4. R119 is exchanged with 150 Ohm resistor. All resistors are surface mount. The result is that the sensitivity is increased in the 0.5 to 1.6 MHz range is changed from -103dBm to -112dBm at 12 dB SINAD,
70% AM. My personal findings are that this do MW listening much more interesting and enjoyable and I have no problems with to strong signal distortion what so ever. SM4RNA Anders
This modification is read 1124 times.
(IC-781) IC-781 General coverage transmit mod
1. 2. 3. 4. 5. Remove power and ant. Remove screws open case. Locate and cut resistor r80 on logic b board. Reset cpu. Reassemble radio.
This modification is read 1007 times.

05-03-1999

(IC-781) 781 ALC Circuit problem
Icom 781 Date 13/05/97 The ALC circuit in the 781 is too slow to respond. This results in the following phenomenon: If you set the power level to 30W, for example, there is a leading pulse that can be more than 200W, particularly if the drive control is advanced. This results in a serious problem if you are using an amplifier. It makes it very difficult to limit drive to an amplifier properly. This behavior is clearly seen on a scope and to some extent on a good peak-reading meter. However I suspect many hams are unaware of the problem as it does not show up on RMS meters due to the short duration of the spike. I have used three 781's over the years ( ser# 19??, 21?? and now 2589) and they all exhibit the same behavior. This behavior is not exhibited by other Icom radios I have checked such as the IC751A, IC735 or IC765. When I had my previous 781, the tubes in my amplifier, a Ten-Tec Titan using a pair of 3CX800A7's, developed shorted grids, even though they were only a few years old and lightly used. I suspected the 781 caused the failure, but sold it before the amplifier was repaired. I recently bought another used 781 from Burghardt radio, serial # 2589, and within 3 weeks of obtaining the 781, my tubes (less than 2 years old) are shorted again. I do not believe this is a coincidence! I run the amp conservatively, and I doubt the tubes have 50 hours transmit time on them. I believe the problem is vaporization of the gold plating from the grid of the 3CX800 causing the tubes to become gassy, which causes arcing. I spoke to Technical Support at Icom USA and was informed that the 781's just work that way and nothing can be done. That is a ridiculous answer! Of course it can be fixed, the attack time in the ALC circuit has to be shortened. This turned out to be easy to accomplish. Locate the following components connected to the base of Q34 in the ALC amp, R107, R108, C47 & C48. These determine the attack and decay time of the ALC amp. Values as per Service manual:

There seemed to be no way of changing the mic button step size to smaller than 100 Hz. An oversight? RS-232 Control Icom's system is called CI-V (Communication Interface 5), and is accessed by a rear panel jack with a bi-directional service. The voltage is TTL ish. You're supposed to buy the CI-V interface which converts to RS232 levels, and also, I assume, de-multiplexes the input and output. The manual only provides a limited description of the control codes required; I guess a full treatise comes with the interface. In particular I couldn't determine what frequency resolution is available via RS-232 control. Other Observations 1. There is a miniature 40mm fan inside the PA section which comes on when the radio is too hot, and the TX is keyed. I spotted the fan on the schematic, but I couldn't find it inside the radio until I provoked it into action during a megabyte file transfer at full power and a 75% duty cycle. The noise is less than a typical computer's. 2. If you want to use speech you must switch your TNC off or disconnect it from the accessory socket, otherwise your speech will be obliterated by data. This is not mentioned in the manual! 3. There is no VOX system. Witticisms The manual is beautifully laid out, with explanations crystal clear, quite devoid of Janglish. Fortunately two useful tips escaped the proof-readers: IF Shift Control, page 24: "Especially in CW mode, a mechanical noise may sound when rotating the [SHIFT] control, however, it is not a transceiver malfunction." I'm still decoding that one. Satellite Notes 1., page 35: "NEVER set the output power too high. Too much power will shorten the satellite's life." Ah so. Conclusion The IC-820H wasn't really designed with satellite operation is its primary application. It's unlikely to win the hearts of serious satellite users, in the same way as Yaesu's FT736R, mainly because of its lack of flexibility. But an average user who wants to try out transponding satellites such as Oscar-13 will find it a satisfactory starting point. With the Pacsats, 1200 bps doppler tracking is awkward, and 9600 bps full duplex operation requires you to modify the radio. The IC-820H is a nice radio if your needs are normal VHF/UHF operating, although serious VHF/UHF users will bemoan the lack of control over external equipment. It is also fine for low speed data transmission, and is the first general purpose radio that provides 9600 bps packet radio simplex capability straight out of the box, at which it excels. Acknowledgement My sincere thanks to Dennis Goodwin at Icom-UK for the IC-820H loan. (C)1994 James Miller G3RUH

This modification is to open the IC-820H for extended receive (and transmit) operation. This is a two (four) step modification which will open the IC-820H to the following frequencies:
VHF Band UHF Band 136 - 174 MHz 420 - 460 MHz
These frequencies are not guaranteed for accuracy or sensitivity. 1. Remove Diode D25 on logic board for VHF RX Expansion. 2. Remove Diode D26 on logic board for UHF RX Expansion. 3. Remove Diode D27 on logic board for VHF TX Expansion. * 4. Remove Diode D28 on logic board for UHF TX Expansion. * * RX modification must be done before the TX modification will work. *
(IC-820) ICOM IC-820H cross band repeat modification
Add a diode on the blank position between D27 & D28 on the Logic Board. The part is 1SS353 P/N 1750000390. After hardware modification 1. Set lock mode. Push [LOCK] 2. Turn Power off. 3. Hold [M/S] and turn radio on. 4. Turn repeater off. Push [LOCK]. Note: If you removed Diode D25 or Diode D26 in the first modification then it can be used in the second modification as it is the same part.
This modification is read 698 times.
(IC-820) IC-820H display board
The following is a partial, not-to-scale, parts placement layout of the IC-820H DISPLAY UNIT circuit board (bottom view). The DISPLAY UNIT is the large circuit board that is located directly behind the front panel. Locating the following four distinctive parts will ensure you have the right diodes: the main dial encoder, the microphone compression level variable resistor (R101), J10 a ten pin header and a row of surface mount resistors immediately above J10. CAUTION: These diodes are NOT labelled sequential! Ensure you are certain of which diode you wish to remove.
| | | []- D28 | BLANK | []- D27 ----| []- D24 [R106] |1o | | []- D26 [R107] | o | | B []- D23 [R108] | o | MIC | O []- D25 [R90 ] | o | J COMP | T []- D22 [R91 ] | o | 1 -----| T [R92 ] | o | 0 | | | O [R93 ] | o | | R101 []- | M [R94 ] | o | | | | [R95 ] | o | -----| | o | | E ----| D | G | E /-------------------------------------| | / | | / | | O | | F | | E N C O D E R | | | | C O P E N I N G | | A | | R | | D | | | | -------------------------------------| | |
UHF TX --> CB RPT --> VHF TX --> UHF RX --> VHF RX --> NOTE 2 -->

-[ -[ -[ -[ -[ -[ -[

/ / | | |
Note 1: The IC-820H Service Manual calls this board the "DISPLAY unit" and the modifications call it the "logic board"; they are one and the same. Note 2: Diode D22 is listed as "[EUR],[AUS] only" in the IC-820H Service Manual.

Radio Model: IC-761, 765 IC-720(A), 735, 740, 745, 751(A), 275A/H IC-725, 726, 728, 729, 736, 737(A) R1 value 47K 2M 220K R2 value 20K 1M 100K
06/01/94 CJR For the IC-820H use the values for the IC-761, 765. The IC-781, IC-765 and the IC-820H all have the same ALC characteristics:
Control voltage Input impedance : -4 to 0 volts : More than 10 K ohms
This modification is read 898 times.

16-04-2001

(PS85) ICOM PS85 fan modification
Author: Mark - pe3hmp@hotmail.com.MODIFICATION.NET When I bought the icom PS85 power supply one thing inmediatly catched my attention, THE NOISY FAN. You would expect if You pay $450 usdollar (in the Netherlands) that this would be a great power supply and not a noisy one ! Well after 2 day I decided that it was time to do someting about it, after contacting icom I heard that there was no mod. for it so I had to do it myselve. This mod is using a NTC to sense the temp and control the speed of the fan so the temp wil not exeed 50 degrees celcius. Potentiometer P is used to adjust the lowest speed of the fan (I set P so that the fan gets at least 6,5V at 20 degrees celcius)
I have tested this mod with a ic-756 and it works great, the noise has gone down with about 50% and the PS85 works as good as before the mod. How to proceed (after building the above)
Remove upper and lower covers.
You must find a place to drill a hole for the NTC close to the diodes
Begin with drilling a hole of 3.5mm (just look on the inside so You wont drill thru a component).
How further up the hole is the better, now You have to tap M4 in the hole (be sure to use a drop of oil).
Now carefully srew in the NTC with a bit of cooling paste on the thread.
Now use 2 sided sticky tape to place the fan control on top of the coil
Connect the NTC, FAN and power and adjust with P the voltage the fan gets (6.5V at 20 degrees celcius). Just trie it and You will be amazed (and think by Yourselve why did'nt came ICOM up with that idea). The cost for all of this was just $10 us dollar and 1 hour of work. Thanks to C@rlos for sending me the schematics. When You turn on the PS85 the fan will start at full speed (to remind You how noisy it can be) after about 2 seconds it will slow down. I thought about replacing the red LED in the front for a dual colour one so You can see what the fan is doing but decided not to that (yet). Any suggestions ? Just e-mail me: pe3hmp@hotmail.com.MODIFICATION.NET

(R-7000) Intermittent display
Author: Burt I. Weiner - biwa@pacificnet.net.MODIFICATION.NET
I have an ICOM R-7000 that has had an intermittent display from the time I purchased it. It has been back several times for repair at an authorized service center. The problem would re-appear after a few weeks. I got tired of sending it back and decided to live with the problem. After a while it became so bad I became too annoyed to live with the problem and decided to track it down for myself. I did discover the actual cause of the problem and after making repair the display has been 100 percent reliable. The problem turned out to be the flat ribbon type cable that runs between the display and the display board. Checking the conductors of the ribbon cable with a meter was misleading because of the intermittent nature of the problem. The repair was a lot simpler than I had imagined. I did not replace or remove the ribbon cable but instead connected parallel conductors across it. The process is simple if you have experience with delicate stuff. It's necessary to remove the display board and the display. First and most important - UNPLUG THE RADIO! Remove the top and bottom cover of the radio. Remove the screws on the left and right side of the front panel brackets that attach it to the main chassis. The front panel will hinge down to about a 45 degree angle. Support it in that position. Remove the 2 screws from the back of the display board. Carefully remove the display board and the metal shield on the back of the board. Carefully swing the board back revealing the component side. Unplug the "dimmer" control plug on the right side of the display board. I found it necessary to cut the tie wraps on the wires connecting to the display board. Be very careful not to cut any of the conductors. Once you've done that you can swing the display board back even farther. Next, remove the two flat head screws on the top of the front panel. This releases the bracket that holds the display against the front panel. Again, be very careful in handling the display. You will notice a foil shield along the bottom of the display ribbon cable. Carefully peel it away exposing the ribbon cable and both ends. I rotated and positioned the board and display so that the pins on both were facing up with the soldered side of the ribbon cable towards me. I used stranded wire from a ribbon cable out of a computer for the jumper wires. DO NOT USE SOLID WIRE! Make the jumpers one at a time. I stripped about 1/16th of an inch of wire, tinned it and then soldered it to one end. Before cutting the other end I dressed it to length following the ribbon cable's "curve" and then cut the other end. Do not make it to tight or leave too much slack. Then I stripped 1/16th of an inch of wire, tinned and soldered it to the other side. Be careful not to bridge any of the connections together. You will note that four of the points, two on each end are connected together. I used only a single conductor for these. Take your time doing this. Check each jumper as you put it in by following the trace in the ribbon cable, which is quite visible, to be sure you are not cross connecting somewhere. JUMPER ALL OF THE CONDUCTORS! If one is intermittent, then the others are or soon will be. When you are finished and just before you start to re-assemble things, carefully clean the display and the inside of the display window with Windex. I used a clean piece of old t-shirt. Rotate the board and display back into position for re-assembly. Re-position the foil shield under the (new) conductors and ribbon cable. I did not replace the tie wraps previously cut but carefully positioned the leads so they do not become pinched under brackets during re-assembly. When installing the display make sure that the fingers at the bottom of the display bracket go under the display easily. Reverse the procedure described above for re-assembly of the rest of the radio. Don't forget to replace the "dimmer" control plug on the right side of the display board once the board is mounted. Since making this repair the display has worked without failure. The sensitivity of the receiver is as good or better than before indicating that the noise output from the display is still well contained. If you have been suffering from the annoying intermittent display as long as I had been this will be well worth the effort. Burt, K6OQK - biwa@pacificnet.net Burt I. Weiner Associates Broadcast Technical Services Glendale, California - U.S.A. biwa@pacificnet.net.MODIFICATION.NET K6OQK