[Icom] IC751A Logic Unit

Wed, 3 Apr 2002 13:43:28 +0200

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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