[Icom] IC751A Logic Unit

Wed, 3 Apr 2002 20:42:51 -0500

that's why i avoid owning a built in PS rig.The design of the ft-990dc is a
radio that will outlast some of us.

tony k2vi
----- Original Message -----
From: "Tomczak, Lech" <[email protected]>
To: <[email protected]>
Sent: Wednesday, April 03, 2002 6:43 AM
Subject: RE: [Icom] IC751A Logic Unit

> This is what I found in the archives (december of 2000) written by Mel
> Martin.
>
> >The problem may be on the logic board. Probably capacitor problems. I'm
> >doing this from memory, so information is approximate. There is a reset
> line
> >on the CPU. When you turn the radio on, there is a RC circuit on the
reset
> >line that holds it low long enough for the CPU to initialize. If the caps
> in
> >this RC circuit are defective, or if the caps on VCC are defective, this
> >problem can result. Good luck...
>
> I am pretty sure that this is my problem. I have localized the problem to
be
> within logic board. Memory RAM is OK. Yeasterday I even got a smoke on
> the logic board. Probably defected capacitor got shorted! I only hope
> nothing else got
> damaged.
>
> I have an internal switch mode PS which makes it all very hot in there
> (placed just above Logic and PLL boards). I have been using this radio for
> at least a couple of hours
> a day since 1986, plus many 48h tests and two DX'peditions. These
> electrolitic capacitors
> must have dried up. I should, I guess replace all electr. capacitors on
both
> PLL and Logic
> boards and remove the PS from the box.
>
> I have also experienced a problem with bad CW signal previously, related
> probably to bad
> electr. capacitors on PLL unit.
>
> Electrolit capacitors and heat over time do not really go together.
>
> 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?
>
> Lech, LA7MFA
>
> > -----Original Message-----
> > From: Ed Myers [SMTP:[email protected]]
> > Sent: Tuesday, April 02, 2002 1:37 PM
> > To: [email protected]
> > Subject: Re: [Icom] IC751A Logic Unit
> >
> > I too have a 751 (not A), Since you replaced the RAM battery 1 1/2 years
> > ago it is unlikely that the RAM has failed. It is possible - of course.
> >
> > Your symptoms sound more like the problem of dried out tantalum
capacitors
> > in the display unit and perhaps other places. I replaced mine some time
> > ago.
> >
> > Go to the ICOM web site and download the information there on the
> > IC-751/751A. The instructions are there.
> >
> > If you have a problem getting them downloaded let me know and I'll try
to
> > help.
> >
> > Good Luck - it is not too difficult and you can usually just bridge the
> > bad ones without removing - unless they are shorted.
> >
> > Ed    WC4TT
> >
> > ----- Original Message -----
> > From: "Tomczak, Lech" <[email protected]>
> > To: <[email protected]>
> > Sent: Tuesday, April 02, 2002 3:59 AM
> > Subject: [Icom] IC751A Logic Unit
> >
> >
> > > I have a problem with the logic (and or display) unit of IC751A.
> > >
> > > My display suddendly started to show 77 in the leftmost position
> > (actually 7
> > > appeard in the
> > > position of a blank!) Some of the digits of display were also wrong.
> > >
> > > After reconnecting the cables between logic and display unit, it
become
> > even
> > > worse,
> > > and now all frequencies start with EE! And now the radio seems to be
> > dead,
> > > except for frequencies 0.100-0.900MHz. Also CW and RTTY does not (do
not
> > > dipslay), but Narrow CW and Narrow RTTY is OK.
> > >
> > > It is maybe a bad connection somewhere, since the problem disappeared
> > for
> > > a while later, and then came back. But how can I track it? Or, maybe
> > this is
> > > the
> > > problem with RAM. I have shifted the battery 1 1/2 years ago, so it
> > should
> > > be OK.
> > >
> > > It is not possible to repair this radio in Norway, so please help.
> > > I do not want to dump it yet. I love this radio!
> > >
> > > 73 de Lech, LA7MFA (ex. KK6HC)
> > >
> > >
> > >
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> > > 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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> Icom FAQ: http://www.qsl.net/icom/
>