[Test-Equipment] UPDATE ON: Does my 141T have a terminal illness?

[Chris Trask]

    One of the syptoms that led to my replacing the 69.8V zener diode on the
mainframe power supply board was that the zener (VR5) was shorted.

    Not sure if Ed Matsuta is still around.  He made his living selling
photocopies of manuals for any piece of equipment he could get an original
manual for.  To find that zener you need the PC board map (Figure 8-11, page
8-16) as they did not put much silkscreen on those boards.  If you can't
locate a manual, let me know and I'll scan the map and the schamatic for
you.

Chris

     ,----------------------.       High Performance Mixers and
    /    What's all this     \    Amplifiers for RF Communications
   / extinct stuff, anyhow?  /
   \  _______,--------------'           Chris Trask / N7ZWY
  _ |/                                  Principal Engineer
 oo\                                  Sonoran Radio Research
(__)\       _                             P.O. Box 25240
  \  \    .'  `.                     Tempe, Arizona 85285-5240
   \  \  /      \
    \  '"        \                 IEEE Senior Member #40274515
     .       (  ) \
      '-| )__| :.  \              Email: christrask at earthlink.net
        | |  | | \  '.       http://www.home.earthlink.net/~christrask
       c__; c__;  '-..'>.__

                       Graphics by Loek Frederiks

----- Original Message -----
From: "jeremy-ca" <km1h at jeremy.mv.com>
To: "Chris Trask" <christrask at earthlink.net>;
<test-equipment at mailman.qth.net>
Sent: Wednesday, August 01, 2007 11:52 AM
Subject: [Test-Equipment] UPDATE ON: Does my 141T have a terminal illness?


> Both fuses on the 6552B IF section are blown, they are for -10 and -12.6V.
> Replacing them gave the same results. The small power transistors next to
> them test OK. Thats as far as Ive got so far.
>
> Im getting nowhere trying to dl a manual from BAMA or the edebris mirror.
> All dl's come up with 0 bytes. This happens on 2 different PC's
>
> Any ideas before I dig in and make it worse?
>
> Carl
> KM1H
>
> ----- Original Message -----
> From: "Chris Trask" <christrask at earthlink.net>
> To: "Alan Melia" <alan.melia at btinternet.com>;
> <test-equipment at mailman.qth.net>
> Sent: Tuesday, July 31, 2007 9:02 AM
> Subject: Re: [Test-Equipment] re: Does my 141T have a terminal illness?
>
>
> >    There's one in particular on the board on the bottom side of the
> > mainframe.  It's a 47.5K (I think) 1% 1/2W wirewound resistor that's
> > actually dissipating over 0.6W.  I had one burn out and replaced it with
a
> > 47K 5% 1W.  It's been working fine ever since.  I seem to recall that
the
> > symptoms of the failure were similar to what you described.
> >
> >    I also had one blow out a 68V zener on that board when we had a power
> > mains surge.  It was harder to find the zener than it was to replace it.
> >
> > Chris
> >
> >     ,----------------------.       High Performance Mixers and
> >    /    What's all this     \    Amplifiers for RF Communications
> >   / extinct stuff, anyhow?  /
> >   \  _______,--------------'           Chris Trask / N7ZWY
> >  _ |/                                  Principal Engineer
> > oo\                                  Sonoran Radio Research
> > (__)\       _                             P.O. Box 25240
> >  \  \    .'  `.                     Tempe, Arizona 85285-5240
> >   \  \  /      \
> >    \  '"        \                 IEEE Senior Member #40274515
> >     .       (  ) \
> >      '-| )__| :.  \              Email: christrask at earthlink.net
> >        | |  | | \  '.       http://www.home.earthlink.net/~christrask
> >       c__; c__;  '-..'>.__
> >
> >                       Graphics by Loek Frederiks
> >
> > ----- Original Message -----
> > From: "Alan Melia" <alan.melia at btinternet.com>
> > To: <test-equipment at mailman.qth.net>
> > Sent: Tuesday, July 31, 2007 2:40 AM
> > Subject: [Test-Equipment] re: Does my 141T have a terminal illness?
> >
> >
> >> Hi Carl dont panic too quickly  :-))
> >> The sweep is quite dependent on the correct psu voltages. The 141 frame
> > has
> >> a habit of cooking some of the resistors which drift high. You will
need
> >> a
> >> 141T manual from one of the several free sites and then before doing
> >> anything else check and re-adjust the 4 power rails to spec. They must
be
> >> done in the correct order, as in the manual. I suspect the -12v rail as
> > this
> >> provides a reference for the schmidt that trips the sweep. I had a
> >> similar
> >> effect on one of my frames which would not sweep below 10ms.
> >>
> >> Good Luck with it
> >> Cheers de Alan G3NYK
> >>
> >>
> >> ______________________________________________________________
> >> Test-Equipment mailing list
> >> Home: http://mailman.qth.net/mailman/listinfo/test-equipment
> >> Help: http://mailman.qth.net/mmfaq.html
> >> Post: mailto:Test-Equipment at mailman.qth.net
> >>
> >>
> >> --
> >> No virus found in this incoming message.
> >> Checked by AVG Free Edition.
> >> Version: 7.5.476 / Virus Database: 269.10.25/926 - Release Date:
7/29/07
> > 11:14 PM
> >>
> >>
> >
> > ______________________________________________________________
> > Test-Equipment mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/test-equipment
> > Help: http://mailman.qth.net/mmfaq.html
> > Post: mailto:Test-Equipment at mailman.qth.net
> >
>
> ______________________________________________________________
> Test-Equipment mailing list
> Home: http://mailman.qth.net/mailman/listinfo/test-equipment
> Help: http://mailman.qth.net/mmfaq.html
> Post: mailto:Test-Equipment at mailman.qth.net
>
>
> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.5.476 / Virus Database: 269.11.0/929 - Release Date: 7/31/07
5:26 PM
>
>