[Icom] IC751A Logic Unit

Mon, 8 Apr 2002 13:26:54 +0200

I have found the problem! There was  a short circuit somewhere
on th Voice Synth. Unit or on the cable connecting it to J12 plug on Logic
Unit.

It was short circuiting bit 2 of data bus coming from the latch holding
current
frequency. This explains why I got 0 instead of 4, 1 insted  of 5 etc. on my
display.

Somtimes I would also get a smoke from R20 on Logic Unit when I switched on
the
radio. This would probably happen when the last visited frequency was one
with
many 4, 5, 6 or 7's in it. It is actually working as an early warning if any

of data buses driven by 5V regulator gets shorted. Inspect this one if you
have any problems on Logic Board! For debugging it is a good idea to connect
only 
those connectors which are needed, starting with 13,8V and so on.

Thanks to all who contributed with hints and ideas.

Lech, LA7MFA

> -----Original Message-----
> From:	Ed Myers [SMTP:[email protected]]
> Sent:	Wednesday, April 03, 2002 4:42 PM
> To:	[email protected]
> Subject:	Re: [Icom] IC751A Logic Unit
> 
> I can beat 10 years!
> 
> My experience with the IC-751 that I bought new before the IC-751A
> appeared:
> 
> Mine does not have a built-in PS. The only caps replaced so far have been
> those in the display. The plastic trimmers have not been replaced. The RAM
> was replaced with one of the after-market non-volatile RAMs at about 8
> years - battery still good.
> 
> This rig has been on a 24/7 MARS PACKET BBS since 1991. Perhaps the good
> results are due to the fact it uses an external ASTRON PS. Perhaps also
> there is some benefit from it being on full time. Also, it is located in a
> basement "shack" where the temp runs 65 - 70 F year round.
> 
> It still doesn't drift but the display is getting "flaky" again. I have
> just taken it off line to do some maintenance.
> 
> The BBS also has a 735 running about 8 years with no problems. These old
> rigs may lack some of the new bells and whistles but they are real
> workhorses in applications like a BBS.
> 
> Ed WC4TT
> 
> 
> ----- Original Message -----
> From: "John Heacock" <[email protected]>
> To: <[email protected]>
> Sent: Wednesday, April 03, 2002 8:30 AM
> Subject: Re: [Icom] IC751A Logic Unit
> 
> 
> > Sure! with the way most equipment is obsolete and not worth using after
> 3-5
> > years, 10 years use sounds like good service.
> >
> > John Heacock, WD5JGA
> >
> > ----- Original Message -----
> > > Still I am dissappointed with ICOM. With this internal switch mode PS
> > option
> > > they have
> > > created a radio which for an active ham is good for 10 years! Not to
> > mention
> > > the RAM problem!
> > > Should I buy ICOM next time?
> >
> >
> > ----
> > Your Moderator: Dick Flanagan W6OLD, [email protected]
> > Icom FAQ: http://www.qsl.net/icom/
> >
> 
> ----
> Your Moderator: Dick Flanagan W6OLD, [email protected]
> Icom FAQ: http://www.qsl.net/icom/

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