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IC-746 FAQ

Service Manual Discrepancies

The "Service Manual" is supposed to be the best, final word on the electronics within the IC-
746. However, the data it contains isn't always consistent. Here are the known
discrepancies.

Identity of Q302

Q302 on the S-Logic Board is a driver transistor for the LCD backlight. It's listing varies
depending upon the reference within the Service Manual. We'd love to hear which part is
actually in your rig.

p.

6-1 Parts

List

2SB1201-S-TL

p. 8-1

Semiconductor Information

2SB1201 S

p.10-1

Block

Diagram

2SB1202

p.11-2

Voltage Diagram (schematic)

2SB1201

We believe the part is supposed to be a 2SB1201.

Identity of R1271

R1271 on the Main Board is a dry reed relay for switching the SEND signal used to operate
external RF power amplifiers. It's listing varies depending upon the reference within the
Service Manual. We'd love to hear which part is actually in your rig.

p.

6-12

Parts

List

OMR-109F

p.11-4

Voltage Diagram (schematic)

AHY103

The Board Layout on page 9-7 clearly shows that the R1271 has a completely different
layout than either R1111 or R1291, which are identified as AHY103 relays in both the parts
list and the schematics.
We believe the part is supposed to be an OMR-109F.

Page 102 of 113

2003-02-08

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Summary of Contents for IC-746

Page 1: ...m IC 746 FAQ Frequently Asked Questions About the Icom IC 746 HF VHF Transceiver Coordinator Dana Hoggatt KB9SSS kb9sss arrl net Copyright c 2001 2002 2003 by Dana Hoggatt all rights reserved Page 1 of 113 2003 02 08 ...

Page 2: ...ut circuit schematics 2003 02 03 Added a Canadian repair center 2003 02 03 More info on LCD scratch removal 2003 02 02 Added ACC 2 pin out diagram 2003 02 02 Added ACC 1 pin out diagram 2003 02 02 Added MIC pin out diagram 2003 02 01 Added errata about receiver selectivity 2003 02 01 Added extensive info on low RF output power 2003 02 01 More non 746 information links 2003 02 01 Add Q A on intermi...

Page 3: ...ls 15 2 8 Are there electronic copies of the circuit schematics 15 2 9 Are there electronic copies of 746 service manuals 16 2 10 How do I fix the font substitution error in the PDF manual 16 2 11 How does an IC 746s differ from an IC 746 16 2 12 What is the IC 7400 17 2 13 What is the IC 746 PRO 17 2 14 Where can I find info on other Icom rigs 18 2 15 Where is info on the 706 718 756 765 735 18 2...

Page 4: ...he internal ATU 35 3 2 18 How do I switch between more than two antenna ports 35 3 3 MICROPHONES 37 3 3 1 What is the best microphone to use with the IC 746 37 3 3 2 Can I hook up a different microphone directly to the IC 746 37 3 3 3 Can I use a Heil microphone with the IC 746 38 3 3 4 How do I adjust the IC 746 for a Heil headset 38 3 3 5 Do I need a pre amp to use a Heil microphone 38 3 3 6 Wha...

Page 5: ... 55 4 14 What are the 455Khz IF filters best for 55 4 15 How do I get the best results from TPBT 55 4 16 How do I configure the IC 746 to use an optional filter 56 4 17 How do I configure the IC 746 to use a non Icom filter 56 4 18 How do I use a CW filter in SSB mode to receive PSK31 56 4 19 Why is there only one optional 455Khz IF filter slot 57 4 20 Any tips on installing 9Mhz Inrad filters 57 ...

Page 6: ...don t my band edge beeps match the US amateur bands 74 6 10 Can I transmit all the way out to the band edge beeps 74 6 11 Can I reprogram the band edge beeps 74 6 12 Do we know anything about the band edge beeps 74 6 13 How I reset back to factory default settings 75 6 14 What birdies does the IC 746 have 75 6 15 How do I adjust the LCD display 76 6 16 The Noise Blanker doesn t seem to do any good...

Page 7: ... can I get replacement microphone connectors 93 8 9 What is Lo Fi SSB operation 93 8 10 What is Hi Fi SSB operation 93 8 11 How does one improve the fidelity of a received signal 94 8 12 How does one improve transmission fidelity 95 8 13 Can the IC 746 transmit at less than 5 watts 95 8 14 How do I turn on both HF pre amps at the same time 95 8 15 How do I adjust the 746 for best AM performance 96...

Page 8: ...Page 68 Unclear Voltage Specification 101 Page 70 Overoptimistic SWR Specification 101 Page 77 Unclear UT 102 Installation Instructions 101 Page 79 Incorrect SEND Relay Specifications 101 Page 84 Incorrect Bandwidth listing 101 SERVICE MANUAL DISCREPANCIES 102 Identity of Q302 102 Identity of R1271 102 GLOSSARY 103 CONTRIBUTORS ACKNOWLEDGEMENTS 105 DISCLAIMER COPYRIGHT 108 REVISION HISTORY 109 Pag...

Page 9: ...ly to news rec radio amateur equipment usually sometime between the 1st and the 10th You can post questions comments about the FAQ to the above newsgroup Long Answer The format of this FAQ should become apparent right from the start Questions are grouped into related sections and subsections roughly in the form of an outline When possible practical there will be both a short and long answer The sh...

Page 10: ... rec radio swap Specific comments or clarifications can be sent directly to the FAQ coordinator Content submissions would be greatly appreciated However general discussion debate over the answers is best done in a more public forum like one of those mentioned above 1 4 What are the future plans for the FAQ Starting in February 2003 this FAQ went from a text ASCII format to Adobe Acrobat PDF format...

Page 11: ... and reverse operation More information is needed on the front panel power switch and its interaction with the extra pins on the T connector in the back More service and repair information Better explanation of band stacking registers Operating tips Instructions on how to use internal ATU Better explanation of COMP gain FM etc Compare contrast the 746 vs 746PRO Does the 746 exhibit a full power sp...

Page 12: ...articular interest might be the on line copy of the instruction manual Most of the 746 s problems or faults show up either in this FAQ eventually or in one of the archives at http groups yahoo com group IC746 files IC 746 Brochure pdf http mailman qth net mailman listinfo icom 2 3 How does the IC 746 stand up to the ______ Probably the most objective quantitative comparisons you will find are the ...

Page 13: ...net for amateur radio gear are the USENET newsgroup news rec radio swap and the infamous eBay auction site http www ebay com Amateur Radio Trader is both a magazine and a WWW site devoted to amateur radio classifieds http www amradiotrader com site not responding Jan 2002 Yahoo has a small auction site as well http list auctions shopping yahoo com 23761 category html alocale 0us After those you ha...

Page 14: ...rst Sunday of April through last Sunday of October the net starts at 0100 UTC Monday For the curious not all of the U S A participates in daylight savings time Likewise portions of Europe participate but on a different timetable A wealth of information on DST can be found via Yahoo at http dir yahoo com Science Measurements_and_Units Time Daylight_Saving_Time or within the AC6V link indices at htt...

Page 15: ...heir WWW site at http icomamerica com support documents index html A backup copy of the above manual is available from several locations http groups yahoo com group IC746 files IC 746 Instruction Manual pdf http www qsl net kb9sss IC 746 IC 746 Instruction Manual pdf Additionally the FCC posted the IC 746pro instruction manual and various other documents at http gullfoss2 fcc gov cgi bin ws exe pr...

Page 16: ...cument PDF page 12 A font required for font substitution is missing An error has occurred that may be fixed by installing the latest version of the Japanese Language Support package Unable to find or create font Ryumin Light Identity H Some characters may not display or print correctly The error is not fatal There are about dozen places in the manual where text in diagrams will show up as a series...

Page 17: ...tal noise blanker Digital TX RX equalization instead of analog Digital speech compressor instead of analog Digital voice recorder You ll notice how prominently the DSP plays in this rig One thing the original 746 has over the 746 PRO is an additional IF stage thus its TPBT is actually going through two offset IF filters The 746 PRO achieves its TPBT via the DSP It is argued that the DSP filtering ...

Page 18: ...7400 html http www qsl net ab4oj icom ic7400 ic7400 html 2 14 Where can I find info on other Icom rigs 2 15 Where is info on the 706 718 756 765 735 This FAQ is devoted to the IC 746 As of November 2001 we do not know of any FAQ s devoted to other Icom models However as of Jan 2002 a project was underway to start accumulating and centralizing Icom information at http www qsl net icom While the coo...

Page 19: ...ion pages http www sweb cz ok1fig ic751a htm http www qsl net ab4oj icom 751a_pbt html http www qsl net ab4oj icom icom html IC751A http www piexx com cgi bin piexx cgi p ICOMProm cart_id 1452031 27134 http www piexx com cgi bin piexx cgi p ux14 cart_id 4031494 24744 IC 765 information pages http www execulink com dstalk Last but certainly not least AC6V has a wealth of links and resources on amat...

Page 20: ...C 736 and IC 706MKII Transceivers Hewitt Paul WD7S May 2000 QST p 33 Operating via the ACC connector thus bypassing the SEND relay this project provides automatic amplifier keying with ALC selection based on the Icom band signal An External Amplifier C ontrol Circuit for the IC 706 MK2 Hauff Fritz W3NZ September 1999 QST p 80 Hints Kinks The IC 706 and IC 746 have nearly identical external amplifi...

Page 21: ...DX February 1993 QST p 37 Computer control interfaces for several makes and models of transceivers including Icom http www arrl org members only tis info pdf 9302037 pdf A Low Cost PC Interface for ICOM Radios Thompson Nigel KG7SG July 1992 QST p 37 One of the early original designs for a homebrew CI V interface How To Build A Super Simple Computer Interface For The Kenwood TS 440S And ICOM IC 735...

Page 22: ... of 5 1675 MHz USB can be treated as part of the 60m band Yes the IC 746 can receive the 60m band and does so quite nicely No as shipped the IC 746 will not transmit on the 60m band No there is no 60m specific mod to the rig Yes there is an all band mod that will allow the IC 746 to transmit on the 60m band See http www mods dk Of course once you ve opened up ALL of the bands this way appropriate ...

Page 23: ...oads too easily Kenwood PS 30 overloads too easily Diamnond GZV 4000 RF hash on 40 20m Icom PS 85 RF hash Long Answer This question typically arises for one of two reasons Either someone wants to buy a new power supply or they have an existing power supply that they want to use In both cases the issues are load capacity size weight electrical noise mechanical noise cost features and appearance Buy...

Page 24: ...kewise hearing tolerance varies from operator to operator Thus it s hard to tell in advance if a specific supply will have a problem Time may yet tell We do know that fans are driven by load The closer you operate to a supply s capacity the more the fan runs Also some of the transformers used in linear supplies will generate an audible hum The transformer itself vibrates with the AC supply Mass se...

Page 25: ...F power to help match your load to the supply You could even run the IC 746 QRP drawing as little as 3 4 amps on transmit Another factor is operating mode Some of us have measured full key loads as high as 21 22 amps Normal SSB transmit at full power draws 6 15 amps But FM digital and CW will generally pull 18 20 amps at full power Consider the following measurements on 20m into a dummy load Conti...

Page 26: ...2 Our units will shut down at surge At 25 amps surge the power supply will shut down at about ten seconds So while it is theoretically possible most people do not use supplies rated less than 20 amps continuous In fact most use substantially bigger supplies Bigger Supplies Why use a bigger supply There are several reasons As noted earlier the closer you operate a supply to its rated capacity the g...

Page 27: ...SSB QRP and get by with less than 5A But in an emergency you and your gear may be called upon to operate in different modes at higher power and with heavier duty cycles Planning ahead for the worst case usage helps prevent an untimely failure at just the wrong time Conclusion So you ll find most of us with power supplies ranging from 20 to 30 amps continuous and some with even bigger supplies Page...

Page 28: ...pic the ARRL has a couple dozen of them A good one to start with is The ARRL Antenna Book At over 800 pages and over 1 000 antennas you re sure to find SOMETHING that fits your style and budget For more information try hanging out on one of over 50 e mail groups on the topic at http groups yahoo com group IcomRadio or visit one of the hundreds of antenna oriented WWW sites indexed by AC6V http www...

Page 29: ...he internal ATU Even he was surprised 3 2 5 Are there any tips to using the ATU You mean besides the tips already provided on page 58 of the Instruction Manual Yes The ATU appears to pay attention to the reflected power not the SWR Note we d love someone to analyze the schematics to confirm or deny this This is evidenced by two effects When starting from a close match at QRP power levels the auto ...

Page 30: ...cularly when bypassed Some speculate that tuning with low power is safer than tuning with high power if nothing else its at least more polite We need more information on this but at least you ve been warned The best procedure we can suggest at this point is Turn off the internal ATU Reduce power to about 1 4 25w Adjust the external ATU using the rig s SWR meter The two meters usually disagree It i...

Page 31: ... beverage antenna than just impedance matching Beverage antennas tend to sacrifice gain in order to improve their signal to noise ratio So while they are good for receiving they are poor for transmitting Therefore you would typically use a separate antenna for transmitting Split VFO Method While not convenient the IC 746 can be configured to use one of its antenna ports for transmitting and the ot...

Page 32: ...tuner Tuning at the antenna is far more efficient than tuning in the shack feedline SWR etc however tuning in the shack is more convenient no power or control cables Icom tuners will be plug n play with the IC 746 while third party tuners may require cabeling or a change in procedure Remember the transceiver s internal ATU must always be disengaged when driving an external tuner Cascading tuners c...

Page 33: ...tp www hamoperator com ah4 ah4 htm AH 3 The AH 3 is an older out of production alternative to the AH 4 it covers 1 8 to 30 MHz continuous with a 7m wire antenna There is info on it at the following WWW site http www qsl net n4pl ah3 AH 2 Older still the AH 2 could cover 1 8 to 30 MHz with a 12m antenna or 3 8 to 30 MHz with a 3m antenna 3 2 14 Can the TUNER button activate an external automatic AT...

Page 34: ...6 all Icom rigs from this era use the same circuitry connector 3 2 15 Why doesn t the rig SWR meter match my external SWR meter Its normal for different points along the RF feed to register different SWR readings The SWR meter in the 746 reads the SWR between the final amplifier stage and the tuner Your external SWR meter reads the SWR between the tuner and the antenna The external meter should al...

Page 35: ...ily but then I don t know the signals that they receive under normal circumstances Notice also from the specifications that each part really has 2 internal diodes By looking at the schematic for the radio that comes with your Owners Manual D8 and D9 both have open leads where one diode is NOT used They are on OPPOSITE sides What you can do one time only is to swap D8 and D9 and the radio should wo...

Page 36: ...IC 746 FAQ Page 36 of 113 2003 02 08 ...

Page 37: ...rum that most contribute to understandability Their great performance have made them very popular For those of you who want it all Heil even makes a microphone that switches both ways literally It has two pick up elements in the same mic so you can change between ragchewing and DXing punch at the flick of a switch Who says you can t have your cake and eat it too 3 3 2 Can I hook up a different mic...

Page 38: ...ugh microphone gain to use an unaided Heil microphone Heil s May 2000 newsletter discusses this topic see http www heilsound com newslettermay00 htm In short you use moderate mic gain 50 75 12 3 o clock position along with moderate compression 8 10db 12 1 o clock position for the best results 3 3 5 Do I need a pre amp to use a Heil microphone While the above procedure works for most rigs it does n...

Page 39: ... http members aol com ampmicro Another interesting design can be found at http www muzique com ssm2166 gif 3 3 6 What are the pin outs on the microphone connector As listed on page 67 of the Instruction Manual 1 mic input 2 8V DC Output at up to 10ma 3 freq up down 4 Main readout squelch switch 5 PTT 6 GND PTT 7 GND MIC 8 AF Out varies with AF center pin Page 39 of 113 2003 02 08 ...

Page 40: ...programming details Long Answer FOR A STRAIGHT KEY OR EXTERNAL KEYER For a diagram on how to wire the stereo plug see page 68 of the Instruction Manual For a straight Key or keyer wire only the tip and the Sleeve and leave the ring as No Connect tip ring sleeve oooo 2 cond wire to key keyer nc The back key jack is a mono 1 4 inch phone plug and is easy to wire When using the front Jack You also ha...

Page 41: ...ixth menu KEYER TYPE Use the Main tuning knob to set the type of keyer to Elec Key or bug Key to use the bug without electronic keyer 3 4 4 Can I use the internal and external keyers at the same time Sure you can have an iambic keyer plugged into the front and a straight or external electronic keyer plugged into the back You can then use either interchangeably We don t yet know of anyone brave eno...

Page 42: ...ow the exact frequency on the computer screen the IC 746 is tuned to 5 As you change bands on either the IC 746 or the software the IC PW1 will follow that band change If you change bands on the software both the IC 746 and the IC PW1 will follow that band change Paraphrased thanks to WA0SXV the procedure is Turn everything on set the 746 to full power and key up in RTTY Adjust the ALC pot on the ...

Page 43: ...runs from 0 to 4 Vdc W7DS designed a circuit to aid in automatic amplifier band switching that may be useful to you Check out the mods section of this FAQ for more details 3 5 4 Do I really need an external amplifier switching relay Most likely yes If you hook up a non Icom amplifier that does not have a solid state keying interface then you ll probably want an external switching interface This is...

Page 44: ...xplain the failures it makes some of the successes almost unbelievable On the other hand the archives for February 2002 show that tech support told N1JM that The real scoop is UP TO 16V OR UP TO 2 amps Again Icom recommended an isolation relay While the techs did not agree upon the ratings they did agree upon using the external relay Unfortunately none of the answers from tech support have adequat...

Page 45: ... info from the datasheet Max Switched Voltage AC 120V DC 60V Max Switched Current 1A OMR F 0 5A OMR H Max Switched Power OMR F 50VA 50W OMR H 10VA 10W Max Switching Rate 300 ops min no load 30 ops min rated load Operate Time 1 0 msec Release Time 0 5 msec Expected Mech Life 100 million operations no load Expected Elec Life 1 million operations rated load First we see that the listed current voltag...

Page 46: ...d reach the expected mechanical life of the part after less than 3 000 hours of transmitting But wait if we apply that same rate to the expected electrical life we get less than 30 hours of transmitting time In contrast AM FM SSB RTTY operation would likely require 200 000 to 2 000 hours respectively of operating time to hit either expected lifetime The Schematics The schematic on page 11 4 of the...

Page 47: ...s by tapping the relay till it frees but YMMV Actually it takes a fair amount od disassembly to access the relay and this solution is temporary at best 3 5 7 Where can I get an external switching relay You have several to choose from Ameritron ARS 702 Ameritron ARB 704 MFJ ARB 702 I MFJ ARB 704 W2ENY Amplifier Interface Yaesu FRB 757 Users of older amplifiers like the Heathkit SB 200 will want to ...

Page 48: ...e voltage load polarity requirements of your amplifier your choice of SEND jack keying or ACC port keying and your choice of relay or solid state switching The send relay in the IC 746 and others closes 10 to 11 milliseconds before the start of the RF and opens about 7 milliseconds after the end of the RF If you use a relay between the rig and the amp it had BETTER BE FAST The relay in the amp nee...

Page 49: ...g and tightening the metal box and covers will help Additionally Icom recommends changing out leaky bypass and filter capacitors 3 5 11 How do I hook up a Yaesu Quadra VL 1000 amp to an IC 746 The RF ALC and SEND connections are pretty straightforward The only truly tricky part is getting the band select data from the IC 746 to the VL 1000 Fortunately AB4OJ Adam has already forged the way The deta...

Page 50: ...IC 746 FAQ 3 6 TNC 3 6 1 How do I hook up a TNC to the IC 746 Check out the wiring diagrams available at http www packetradio com tnc to radio htm Page 50 of 113 2003 02 08 ...

Page 51: ... hz 1 5 SSB Inrad 123 9 Mhz 2 800 hz 1 5 SSB wide Icom FL 103 9 Mhz 2 800 hz 1 8 SSB wide Inrad 306 455 Khz 125 hz 2 1 CW narrow might not fit Inrad 122 455 Khz 250 hz 1 8 CW narrow Icom FL 53A 455 Khz 250 hz 1 9 CW narrow Inrad 116 455 Khz 400 hz 1 7 CW Icom FL 52A 455 Khz 500 hz 2 0 CW RTTY narrow Inrad 322 455 Khz 1 800 hz 1 5 SSB narrow Icom FL 222 455 Khz 1 800 hz 1 7 SSB narrow Inrad 314 455...

Page 52: ...l filters 1 539 at the last count Most of them will make sense i e be useful to someone somewhere As it is a matter of style and situation ultimately the choice will be up to you We ve broken up this issue into several questions each targeting a more specific issue or problem Short of writing a book it is the only hope of providing any useful answers At the end of this section we ve listed some po...

Page 53: ... bandwidths reject more noise and improve sensitivity Wider bandwidths provide better fidelity Narrower bandwidths also reduce the number of simultaneous signals the rig can hear This reduces the AGC pumping action caused by nearby signals particularly important for CW and digital modes Smaller tighter shape factors reject more noise and improve selectivity Larger wider shape factors generate fewe...

Page 54: ...ead when a CW PSK31 filter gets too narrow you start to experience the auditory equivalent of tunnel vision This can make it difficult to scan around for signals One of the handy things about TPBT is that you can narrow your effective IF filtering bandwidth at any time 4 10 What s the difference between IF filters from Inrad vs Icom Inrad filters tend to have a superior shape factor to Icom s smal...

Page 55: ...ss expensive There are other differences filter blow by ultimate rejection earlier roofing etc but usually it all comes down to cost When money is no object you ll want to use one of each On a tight budget you ll do fine with whatever you can afford 4 13 What are the 9Mhz IF filters best for When dealing with interference from nearby signals the sooner you reject the unwanted signals from your RF ...

Page 56: ... have to lie to the rig All of the IC 746 filter settings are on the basis of Icom part numbers This is supposed to make things easier for new operators Just tell the rig you ve installed the Icom crystal that most closely matches the one you re actually using Lying to the rig does have a side effect The 746 cannot actually shift the IF filters passbands Instead the 746 shifts the local oscillator...

Page 57: ...ation When you have the rig opened if you go on a line from the 9 Mhz filters then to the 455 Khz filters and keep on going towards the front panel you will see a square metal plate on the circuit board He mounted his second filter on top of the metal plate on its side and it seems to work fine However KE5DC reports that is very difficult to prevent the cover from coming into contact with the filt...

Page 58: ...rtant receiver specs However the filter is unpopular Most hams simply have trouble justifying 100 200 for a filter they already have the stock filter has the same bandwidth Given that caveat here are some popular filter combinations you might want to ponder None Single 500hz wide CW filter in either IF Dual 500hz wide CW filters one in each IF Single narrow SSB filter in either IF Dual narrow SSB ...

Page 59: ...ft and will require a 1 8 inch stereo to mono plug adapter for use with the IC 746 When you buy the RS 746 remote control software from ICOM it comes with a single rig cable OPC 662 or OPC 478 W2ENY sells a complete CT 17 clone and a single rig cable They re both more complete package than Icom s coming with cables and software resources on a CD ROM They re also cheaper You can find out more at ht...

Page 60: ...CIVInterface htm http www oz1eqc dk Downloads htm http www g3vgr co uk civ htm The OZ1EQC version of the circuit allows the use of the same COM port for both CT 17 control and RTS style keyer control The software configuration implications are left as a puzzle for the reader When building the G3VGR version AD6ZU makes the following observations I found that the G3VGR interface to be quite easy to ...

Page 61: ...om11 html K1NU ICOM Computer Control Interface http home att net k1nu k1nu Products RTS 01 Computer Interface cable for Icom HF Radios http rtsars com othercables_template cfm http www sarrio com sarrio w1gee html 5 4 Do I need a special cable to connect a CT 17 to an IC 746 No the cable is a simple 2 wire cable with a 1 8 miniature phone jack on each end When homebrewing some folks don t even bot...

Page 62: ...the below software can be found at http www eham net reviews detail 1499 http www qrz com search pl topic reviews Icom RS 746 software Icom SELLS a program called RS 746 buying it is certainly the path of least resistance It is available through the usual retail channels It comes complete with both software and the necessary cabling OPC 662 Many people describe it as a thing of beauty Of course be...

Page 63: ...s of software and documentation along with the PC to rig interface cables he sells Many of the packages listed here are also on his disk http www geocities com w2eny civ http www geocities com w2eny icom_cable RadioComm Arachnophilia has several programs RadioComm IcomControl and EasyTuner among others Check out the download section on their WWW site is at http www arachnoid com YP Log Tony Field ...

Page 64: ...electable skins You get to choose what you want your radio to look like be it IC 746 IC 706 or even a 007 spy watch More details at http n9zle tripod com ScanCat Very extensive scanning support including automatic digital recording to your hard disk http www scancat com Radio Manager An example of the virtue os simplicity this shareware from KC5IRJ does a lot with minimal resources http www interp...

Page 65: ...o http www buxcommco com Donner s Digital http home att net n8st West Mountain Radio http www westmountainradio com Or you could build an interface You ll need audio in audio out and PTT signals Several DIY plans are available http www qsl net wm2u interface html http www qsl net wm2u psk31 html http www arrl org tis info HTML psk31 index html http www w5bbr com soundbd html http home teleport com...

Page 66: ...d pass 8 11 Mhz band pass 11 15 Mhz band pass 15 22 Mhz band pass 22 30 Mhz band pass 30 50 Mhz band pass 50 54 Mhz band pass 54 60 Mhz band pass 108 174 Mhz band pass Some mistakenly call this the antenna tuner there is even some component overlap however the preselector and tuner serve different purposes and are each switched in and out accordingly 6 3 Why doesn t the ALC meter work while adjust...

Page 67: ...output at the reduced voltage will most likely degrade the quality of your transmitted signal clipping IMD etc Most hams decide that 1 2db gains don t justify the crumby signal There is one more possible remedy for the low voltage problem You could get a DC DC voltage converter These are also called voltage boosters Such a device accepts 12Vdc in and yields 13 8Vdc output There s a price First the...

Page 68: ...ave the service manual on hand and be prepared to readjust realign everything afterwards Blown Output Detector Diodes Blown diodes in the SWR detector can fool the power fold back circuitry into cutting back power unnecessarily The blown diodes will be shorted This can easily happen by playing around with an external antenna tuner in conjunction with the internal ATU Your ALC circuit may have fail...

Page 69: ... fractional db of power is important check out the power adjustment instructions in the mod section of this document The service manual specifies setting R989 for 100W on 14100khz R991 for 100W on 51000khz and R993 for 100w on 145000khz mode set to RTTY rf power pot set fully c wise pots on main unit board the board with the filters on That s three specific adjustments to cover all 11 bands Check ...

Page 70: ... a problem for many 746 rigs as evidenced by the data collected at http groups yahoo com group IC746 database method reportRows tbl 2 It s not the actual lamp itself but one of the driver transistors The lamp is fluorescent and will probably never wear out Even if it did the lamp isn t available as a separate part it s part of an assembly you need to get from Icom Background into problem There is ...

Page 71: ...hield that covers the transistors about six solder connections and then replacing the surface mount transistor And of course reversing the whole process to put the rig back together again The part itself is cheap around 3 00 Feb 2002 If you re tempted to unsolder the control pots from the S Logic board stop and think you re probably doing things the hard way The affected transistors are on the sid...

Page 72: ...olks at MTS suggested a 2SB1202 as a replacement Examining the specifications http www nedis com datasheets datasemi 2SB 2SB1201 pdf http www qsl net kb9sss IC 746 Parts 2SB1201 pdf http www nedis com datasheets datasemi 2SB 2SB1202 pdf http www qsl net kb9sss IC 746 Parts 2SB1202 pdf We can see that the suggested replacement is physically identical to the original part but with 50 higher current ...

Page 73: ... so availability is limited Also as K9HFX discovered there are apparently two versions of the HM 14 The version without the scan button enable disable switch did not work for him More information is needed While not listed on Icom s compatibility charts as such VE2MHF reports that the HM 56A also works even the scan buttons and 14 DTMF memories However beware as VE4HAY reports that the DTMF pad on...

Page 74: ... Yes you can transmit all the way out to the beeps The IC 746 as shipped from the factory can transmit outside of the amateur radio bands This has been tested and confirmed on several rigs via dummy loads 6 11 Can I reprogram the band edge beeps No there is no known way to reprogram the band edge beeps There are no fixes or planned updates from Icom dealing with them You can however turn them off ...

Page 75: ...ort cpureset html amateur While pushing in F INP and M CL push POWER to turn power ON 6 14 What birdies does the IC 746 have Birdies are spurious signals internal inherent to the rig itself They are normally generated by harmonics and or mixing products of the internal oscillators IF VFO display driver CPU clock etc that are picked up by one of the RF IF stages of the rig Birdies are usually perce...

Page 76: ... ANL or DSP a NB will have little or no effect upon static crashes and or white noise Noise generated by power supplies fluorescent lights and power inverters are generally unaffected The NB works best when impulse noise is strong and the signal is weak like mobile in a vehicle Most hams report that the 746 s NB is effective against ignition noise but not as effective as other rigs they ve owned N...

Page 77: ...cable to the IC 746 Put snap on ferrite beads on the electronic ignition wiring bundle Ground engine block to chassis This problem is not specific to the 746 all radios can be afflicted Covering this topic thoroughly is beyond the scope of this FAQ For more help information try the following http www arrl org tis info rfiignit html http www arrl org tis info pdf 001qex32 pdf http www k2bj com Page...

Page 78: ...remedy the problem Use a large rubber band Use a glue stick Use electrical tape Use rubber cement beware that RC might deteriorate rubber leave set hole uncovered to allow front panel removal maybe tack just a few places to allow ring removal 6 20 Where should I go for repairs There are lots of places you could go A few of the authorized Icom service repair centers come highly recommended by other...

Page 79: ... repairs or for older equipment MTS http www angelfire com biz2 mts Email mts plix com Malcom Technical Support MTS 3617 Deep Lake Boundary Rd Colville WA 99114 9142 Voice 509 732 8883 Fax 509 732 8884 Burghardt s http www burghardt amateur com Email hamsales burghardt amateur com service burghardt amateur com Burghardt Amateur Center 710 10th Street SW PO Box 73 Watertown SD 57201 Voice 605 886 7...

Page 80: ...or restoring plastic watch crystals works great on them If it is just an abrasion toothpaste or tooth powder might work or try body polish not wax for a car For fine or hairline scratches you could try a product call Everclear Apply with a cotton ball then remove with a clean cotton ball There s more info on this product at http www onecybersquare com shopping everclear how_to_repair_clear_surface...

Page 81: ...s on the wide band receiver technology but again that doesn t really answer the question Turning on the preamp will increase the reading 6 24 Why is my tuning shaft knob loose and sloppy If the factory did not tighten the nut that holds the main tuning unit then over time movement may cause the friction screw to crack the faceplate This is a hard one to get at 6 25 Why is my audio cutting in and o...

Page 82: ...he mod will not void your warranty That said MARS CAP TX RX modifications for the IC 746 and many other radios can be found at http www mods dk Another source for the TX RX mods is QRZ COM http www qrz com download mods i k ic746 txt Pay close attention as there are two distinct mod procedures which correspond to the differing placement of the programming diodes on the PCB 7 2 What other mods are ...

Page 83: ...eceive line through my patch panel which makes it easy to disconnect it when not in use I also measured a 1 5 db improvement in sensitivity by going directly into the receiver board Finally W8FN Randy says To do this modification you first need to obtain some of the Icom PC connectors used to make internal RF connections The female PC board mount connector is P N 93602690 and the male connector is...

Page 84: ...il cable assembly Plug the male pin from the other pigtail assembly into J1 on the RF unit To minimize the chances of mechanical problems I used plastic tie wraps to bundle the input and output pigtail cables together Once the RF compartment shield is replaced it will hold the cables in place To check your work power up the radio with an antenna connected but no connection to the pigtail jacks You...

Page 85: ...ilter Murata CFJ455K with a superior crystal filter should improve the rig s performance Three obvious choices have been suggested Inrad 109 crystal filter Icom FL 44A crystal filter Kokusai MF 455 11GZ mechanical filter One source of info claims that to do this mod with crystal filters requires changing 2 resistors R701 and R704 from 10K to 3 9K to change the impedance seen by the filter from 2K ...

Page 86: ...mit What about the 746 s internal voltage regulators Increasing the power by 50 more than doubles the RF voltages within the internal ATU Thus making it more prone to arcing and burnout Differing part tolerances can surprise you It s much easier to compensate for component variations when you stay well within their tolerances Thus some rigs may be more prone to the above problems than others Just ...

Page 87: ...COM Transceivers The Millennium QSYer is based upon that design and available from http www john hansen net keypad htm Cordless Headset Microphone Some hams have come up with a clever way to add a cordless headset to their rig Basically you find a cordless phone with a soundcard interface on it something designed to work with your PC as an Internet phone The IBM3330 900Mhz phone is a popular choic...

Page 88: ... com product1 htm 2m TX RX Sequencer G3SEK outlines a complete TX RX sequencer for handling more complicated transceiver transverter amplifier hookups http www ifwtech com g3sek dx book sequencer External Tuner Pulser This is covered in the Antenna Section as well You can make the IC 746 think that there is an ATU out there with a dummy plug like that available from W2ENY at http members fortuneci...

Page 89: ...io so he opened up all of his Icom hand mics and removed the heavy wad of felt that was in front of the mic elements He s receiving much better audio reports now The felt was probably there to prevent popping from consonants like B or P So beware Page 89 of 113 2003 02 08 ...

Page 90: ...ome rigs seem to have problems with the transistors that drive the LCD backlight while some do not This might be due to a circuitry change or a difference in assembly The jury is still out The only way the issue will be resolved conclusively is for someone to organize a data collection effort to sort out these details by serial number So far no one has volunteered 8 2 Can I operate 2m on reduced p...

Page 91: ...nd level 0 5 to 0 8 V dc Output current 20 ma Input current 200 ma 4 MOD Audio input direct to modulator Bypasses microphone preamp and VOX 100 mV rms at 10 000 ohms 5 AF Audio output fixed level Also monitor output when transmitting 100 300 mV rms at 4 700 ohms 6 SQLS Goes to ground when squelch opens Current 0 1 ma 7 13 8 V Unregulated connection to main supply voltage Max Current 1 amp 8 ALC Au...

Page 92: ...dc Output current 20 ma Input current 200 ma 7 13 8 V Connected directly to pin 7 on ACC 1 8 6 Does audio to pin 4 of ACC 1 trigger the VOX No Pin 4 of ACC 1 does not trigger the VOX circuitry nor is the level of that input affected by the front panel mic gain control 8 7 Where can I get replacement power connectors Obvious Solution The connector you need is often called an OEM T connector You can...

Page 93: ...always just snip off the PowerPole connector if you don t want it Many clubs and organizations have been standardizing on the PowerPole connectors for their high amperage 12VDC power This makes all of their equipment inter compatible and interchangeable a real plus in an emergency There s a good article on that subject at http www dcpwr com standard html 8 8 Where can I get replacement microphone ...

Page 94: ...t than most people are willing to invest A lot of Hi Fi activity occurs on or about 14 178 Mhz There is also an active group of hams at http groups yahoo com group hfssbaudio 8 11 How does one improve the fidelity of a received signal Here is a checklist of several possible actions not in any particular order Assure precise tuning Use a high quality external speaker or headphones Try to run withou...

Page 95: ... panel control will only get you down to about 4 5 watts However you can apply a voltage to the external ALC input to get even lower 0 to 4Vdc input yields 0 to 100 Watts output One ham even uses a simple voltage divider pot arrangement powered by 2 AA batteries K5UHF warns that there can be a minute moment of higher power output before the external ALC level kicks in Not normally a problem unless...

Page 96: ...ere s more information on this general topic at http www ntia doc gov osmhome redbook redbook html While I don t have a link for it at the moment I ve been told that MARS Military Affiliated Radio Service must adhere to the same standards For both CAP and MARS some grandfathering did occur however that should have expired by now 8 17 How do I adjust the Noise Reduction NR The level of NR you want ...

Page 97: ... repeater PL tones There are two different tones you might need In the USA PL tones are used while in Europe a 1750Hz tone is used You access them both the same way Page 34 of the instruction manual covers the procedure which we summarize here With the frequency set to somewhere in the 2m band with M1 displayed press the menu button to get M1 displayed if M2 is displayed You ll see TON above the F...

Page 98: ...nal is the same in CW mode as CW R mode By A B comparison you can reliably get to within 5Hz Either of these techniques will work very well There are other approaches but these two are the simplest most convenient and the most popular Yes it can be tough to zero beat a side tone against dits and dahs but it takes very little effort to get close enough to put your signal within the person s passban...

Page 99: ...d be p 19 7 KEY p 24 should be p 23 8 RTY p 30 should be p 29 9 TON p 35 should be p 34 10 TSQ p 33 should be p 32 Page 15 BAND EDGE BEEPS simply do not work as expected This is more a failing of the radio itself than it is an error in the manual For more info refer to the rest of the FAQ Page 19 SSB TX Tone affects more than SSB The SSB TX Tone setting affects the tonal quality of AM and FM trans...

Page 100: ...io drive level ends up being right for all the other modes as well Page 33 Incorrect filter diagram The diagram at the top of the page is incorrect It shows only one stock filter 2 4 Khz wide at the 9Mhz IF There is a second 15Khz wide filter at that point instead of the direct through connection shown Page 42 Incorrect Page Reference Reference for Noise reduction p 39 should be p 40 15Khz filter ...

Page 101: ...between 1 7 1 and 1 3 1 Page 77 Unclear UT 102 Installation Instructions The UT 102 Voice Synthesizer is installed in the bottom of the transceiver not the top Also the shield cover is not involved Page 79 Incorrect SEND Relay Specifications The NOTE for CONNECTING A NON ICOM AMPLIFIER should read NOTE The specifications for the SEND relay are 12 V DC at 20 ma milli amps If this level is exceeded ...

Page 102: ...lock Diagram 2SB1202 p 11 2 Voltage Diagram schematic 2SB1201 We believe the part is supposed to be a 2SB1201 Identity of R1271 R1271 on the Main Board is a dry reed relay for switching the SEND signal used to operate external RF power amplifiers It s listing varies depending upon the reference within the Service Manual We d love to hear which part is actually in your rig p 6 12 Parts List OMR 109...

Page 103: ... Audio Peak Filter ARRL Amateur Radio Relay League ATT ATTenuator ATU Antenna Tuning Unit BCB BroadCast Band BFO Beat Frequency Oscilator CAP Civil Air Patrol COMP COMPression DSP Digital Signal Processing DTMF Dual Tone Multi Frequncy touch tone FAQ Frequently Asked Questions FM Frequency Modulation FSK Frequency Shift Keying IF Intermediate Frequency IMD Inter Modulation Distortion LCD Liquid Cr...

Page 104: ... Wave Ratio TCN Tone CoNtrol SSB transmit cutoff TCXO Temperature Compensated crystal Oscilator TPBT Twin Pass Band Tuning TS Tuning Step TX short for Transmit or Transmitter USB Upper Side Band VFO Variable Frequency Oscilator VOX Voice Operated transmission YMMVYour Milage May Vary standard disclaimer Page 104 of 113 2003 02 08 ...

Page 105: ...s a small token of thanks for their neighborly spirit and generosity The Coordinator apologies if anyone has been missed AA6YQ Dave AB0IO Marv AB2BK Len Davis AB4OJ Adam Farson AC4JF David Waters AD1C Jim Reisert AD5CD David AD6ZU Roy AH6LE Ken Arck AK6R Bob Brehm DF4OR Ekki Plicht Germany EA7KY Julio Maleno Spain EI2JC Noel W Ireland G0HDB Martin Davies U K G4FZN Chris U K G4YTL David U K G4YVM D...

Page 106: ...R Jan Reimers Canada VE2MHF Francois Canada VE3CE Wayne M Canada VE3EXT Jerry Beneteau Canada VE3GWX Peter Canada VE3JKC Keith Carter Canada VE4HAY Derek Hay Canada VE6CGX Tony Hwang Canada VE7MDL Erik Canada VE9FX Lin Canada VK4ZSS Sam Canada W0LSD Ken W0QE Larry Benko W0TLO John W0TUP Arlon N W0VD Dan W1IK Jim Wickstrom W1MCE Dave S W1MNK Jon W2ENY Bob Langston W2MAW Mark Wolf W2VJN George W3UHF...

Page 107: ...ke Foerster If anything then the sheer number of people involved more than 100 contributors from more than a dozen countries should illustrate the collaborative effort involved in producing this FAQ Thanks to everyone involved Page 107 of 113 2003 02 08 ...

Page 108: ...ein Use at your own risk Copyright c 2001 by Dana Hoggatt all rights reserved This FAQ may be posted to any USENET newsgroup on line service WWW site or BBS as long as it is posted in its entirety and includes this copyright statement This FAQ may be distributed as class material on diskette or CD ROM as long as there is no charge except to cover materials This FAQ may not be distributed for finan...

Page 109: ...09 Added Q A about low voltage operation shutdown 2002 09 08 More info on IC PW1 operation 2002 09 06 Added Q A about Alaska Emergency Frequency 2002 08 26 More info on ignition noise 2002 08 20 More info on SEND connection problems 2002 07 17 Added Q A about 60m operation 2002 07 15 Added Q A about IC 2KL amplifier birdies 2002 07 12 Added Q A about loose rubber tuning dial grip 2002 07 12 Added ...

Page 110: ...s 2002 02 27 Added more info on voltage boosters 2002 02 26 Minor editing formatting of mods 2002 02 25 More info on LCD driver repair 2002 02 22 More info on SEND relay limitations 2002 02 21 Added more info on Q302 and LCD burnout 2002 02 21 Added alternative prevention to LCD blow out 2002 02 21 Added mod to MONITOR level 2002 02 21 Updated Q A on external tuner activation 2002 02 20 Added Q A ...

Page 111: ...1 10 Checked and added more manual page references 2001 11 09 Added M E P 42 15Khz filter at 9Mhz IF 2001 11 09 Added M E P 56 use keypad for numbers 2001 11 09 Added M E P 46 COMP GAIN control 2001 11 09 Added M E P 15 band edge beeps 2001 11 08 Added M E P 68 confusing ALC voltage 2001 11 08 Added M E P 46 ALC only on SSB 2001 11 08 Minor updates regarding SWR values 2001 11 08 Added M E P 70 SW...

Page 112: ...ed numerous spelling errors 2001 09 01 Updated Q A on ATU to reflect recently reported damage 2001 09 01 Added Q A about IC 7400 IC 746 MKII 2001 08 28 Updated info buying a 746 2001 08 14 Updated info on accessing the FAQ 2001 08 07 Updated Q A on ATU range 2001 08 07 Updated Q A on ATU tricks band sweeping 2001 08 07 Added Q A about reset to factory defaults 2001 07 25 Added Q A on VOX and ACC 1...

Page 113: ...ed info on rig modifications 2001 05 20 More info on power connectors 2001 05 19 Dayton Hamvention WooHoo 2001 05 18 Updated info about an Icom HF net 2001 05 17 Added Q A about non SSB ALC readings 2001 05 16 Added new info about an Icom HF net 2001 05 15 Added Q A about broken LCD backlight 2001 05 14 More information on power supplies 2001 05 01 First circulated copy 2001 04 20 First rough draf...

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