[Icom] IC-751 FM Unit Schematic wanted

Fri, 25 Jan 2002 07:10:50 -0800

Hi Ed-

Thanks for the reply, that's pretty much what I have found.  Looks like it
was an option but the documentation is really sparse.  I've looked in all
the schematics.  The service manual has full radio schematic that shows most
of the circuits in detail except the RAM board and the FM unit.  However,
the pictorial diagrams show both units clearly as far as part location,
reference designators, etc.  My works fine too, I just want to have it so I
can do a discriminator modification.

I'll keep trying.

Stuart - ki6qp
----- Original Message -----
From: "Ed Myers" <[email protected]>
To: <[email protected]>
Sent: Friday, January 25, 2002 2:39 AM
Subject: Re: [Icom] IC-751 FM Unit Schematic wanted

| My ICOM 751 (not A) Maintenance manual, contains the following information
| regarding FM operation:
|
| Page 3-14 contains FM OPERATION.  Pages 4-2 and 4-4 contain the theory of
| operation of the FM UNIT, Page 5-1, BLOCK DIAGRAM, shows a FM UNIT. On
| page 5-2 there is a block diagram of a FM UNIT. The blocks identify the
| ICs used.
|
| Page 10-13, UNIT WIRING DIAGRAMS (1), shows a box outlined in dashes
| rather than sold lines labeled "OPTION FM". It connects to the MAIN box.
| This indicates to me it was intended to be an optional add-on board.
| However, Section 7 of the manual, OPTION INSTALLATION, makes no reference
| to it.  Perhaps they decided to incorporate it in all 751s but failed to
| change the dashed lines to solid.
|
| I too have found no circuit diagram. There are circuit diagrams of most
| other units. Maybe that circuit is buried somewhere in this large book.
|
| I haven't opened up my 751 to look for a board because it is on-ine 24/7
| running a BBS. But, the FM mode appears to work.
|
| Ed WC4TT
|
|
| ----- Original Message -----
| From: <[email protected]>
| To: <[email protected]>
| Sent: Thursday, January 24, 2002 11:39 PM
| Subject: Re: [Icom] IC-751 FM Unit Schematic wanted
|
|
| > I don't think there is a separate board for FM for the IC-751.
| > The radio comes equipped to receive FM (at least mine did
| > when I bought it new).  I don't have a service manual for the IC-751,
| > but I did get a manual for the IC-751A.  It shows the FM detector as
| > an integral part of the radio, not like the IC-720 and some others
| > where FM required an outboard plug-in board.
| >
| > If you look at Illustration 2-5 which is the Main Unit, you se the FM
| > modulator circuit right in center left section right about the CW, RTTY
| > oscillator section.  I don't think this is a separate board.
| >
| > On the right side, you see the FM IF, FM Detector circuit.  Again,
| > it is an integrated part of the Main Unit and not a separate outboard
| > item.
| >
| > Or perhaps I misunderstood your question.
| >
| > I hope this is helpful.
| >
| > Micheal Salem N5MS
| >
| >
| >
| >
| > On Fri, 25 Jan 2002 00:23:58 -0000 "Michael P. Olbrisch"
| > <[email protected]> writes:
| > >
| > >
| > > > -----Original Message-----
| > > > From: [email protected]
| > > [mailto:[email protected]]On
| > > > Behalf Of Stuart Rumley
| > > > Sent: Thursday, January 24, 2002 3:11 PM
| > > > To: [email protected]
| > > > Subject: Re: [Icom] IC-751 FM Unit Schematic wanted
| > > >
| > > >
| > > > Michael-
| > > >
| > > > Thanks for the offer to help.  I don't know what the model of
| > > > the FM Unit is, its just a small internal board on the main deck.
| > >
| > > > I've looked through the service manual I have an cannot find
| > > > any reference to the board part number or model number.
| > > > What do you have?
| > > >
| > > > Stuart
| > >
| > > What I have is two units.  I have an IC-740 with the FM unit, and
| > > I also have an IC-551D with an FM unit.  Both are back-up radios,
| > > and they are stored away in a place difficult to get to.  If you can
| > > tell me the unit number, like EX-306 of whatever, I can look it up
| > > and see if that is what I have.  Dunno, you may also have the one
| > > that goes in the IC-725.  I don't believe the 751 used the unit
| > > for the IC-551, but it might be the one for the IC-740.  Let me
| > > know.
| > >
| > > Mike.
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