[ICOM] 751A Main RF Board

[EP Swynar]

Hi Gary,

Bingo...! Yes...!

There is, indeed, a "J17" marked on the pc board, right next to the pin
terminal...

What does it all mean, then...? Can I safely install the board into my
existing rig --- minus the black wire / J17 connection --- and expect it to
work OK...?

I assume PBT refers to "push button tuning"...? If I hook-up the board LESS
the wire, will some button on the face of the rig allow me this option, vs.
my simply spinning the dial...?

...And how'd you get so smart about these things, anyway, Gary...?! Hi Hi.
Seriously, it's great to have the knowledge & experience of guys like you
available to aid & abet dunderheads like me...I sincerely do appreciate it.

~73!~ Eddy VE3CUI - VE3XZ

****************************************


----- Original Message ----- 
From: "Gary P. Fiber" <gfiber at comcast.net>
To: "ICOM Reflector" <icom at mailman.qth.net>
Sent: Thursday, October 23, 2008 12:04 PM
Subject: Re: [ICOM] 751A Main RF Board


> On the original board was that post labeled J-17? If do that was the
> defeat for the PBT. You may have a board that PBT is enabled on where
> your original one PBT was disabled from the factory due to a patent
> infringement that was settled years ago now.
>
> Gary K8IZ
>
> EP Swynar wrote:
> > Hi Guys,
> >
> > Here's a good one...
> >
> > A year ago, my venerable back-up rig --- the Icom 751A --- suddenly went
belly-up in the transmitting department. A tekky friend of mine, who is in
the business of consumer electronics repairs, had a good long look at it, &
determined that a 9-MHz crystal-controlled stage on the main RF circuit
board wouldn't oscillate in transmit...no idea why, either (all the parts,
voltages, etc. therein apparently checked A-OK).
> >
> > Anyway, last summer I bought a complete 751A board (less filters) from a
fellow who was parting-out his rig. Great! I'll just swap out the "bad"
board, & replace it with the new one...
> >
> > Well, to-day I proceeded to carefully dismantle my board from the rig,
recording which connector goes where, etc. etc. etc. ... and all went well,
too, until the end, when I finished-up with a black wire that pulls out of a
post at the juncture of diodes D-161 & D162 in my 751A...
> >
> > The problem is, there is no such post on the board that I
purchased...and no diodes D161 or D162, either.
> >
> > I examined my 751A service manual schematics, circuit board outlines,
and parts list --- and learned, to my complete & utter dismay, that these
diodes aren't listed in the manual, either!!!
> >
> > I must have a newer-vintage transceiver which was manufactured AFTER the
manual was printed, or an older transceiver & a new manual --- with a brief
history of any & all engineering revisions made to the rig being NOT duly
noted therein...(sigh!).
> >
> > The black wire goes from the afforementioned post, and plugs into the
Matrix board.
> >
> > I am debating whether, or not, I should simply proceed with the swap &
tape the wire off to one side (the same way automobile manufacturers do with
redundant underhood wires in the face of upgrades) & hope for the best, or
do as my friend did last summer, & simply part this sucker out to the world,
piece by miserable piece...
> >
> > ~73!~ Eddy VE3CUI - VE3XZ
> >
> > PS: How come I never have this problem fixing-up my old Drake &
Hallicrafters rigs...?!
> > ----
> > Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
> > Icom Users Net: Sundays, 1700Z, 14.316 MHz
> > Icom FAQ: http://www.qsl.net/icom/
> >
> >
>
> ----
> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/