Random DEC Questions

Robert Jarratt robert.jarratt at ntlworld.com
Thu Dec 4 17:28:42 CST 2014

> -----Original Message-----
> From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Chris
> Elmquist
> Sent: 04 December 2014 22:58
> To: General Discussion: On-Topic and Off-Topic Posts
> Subject: Re: Random DEC Questions
> On Thursday (12/04/2014 at 02:34PM -0800), Ian McLaughlin wrote:
> >
> > > On Dec 4, 2014, at 2:27 PM, Robert Jarratt
<robert.jarratt at ntlworld.com>
> wrote:
> > > I opened up the VT320 tonight. The PSU is set for 240V, which is
> > > good. However, I noticed some corrosion around the flyback
> > > transformer. I have posted a picture here: http://1drv.ms/1zqDhx5
> > >
> > > This looks like corrosion of some kind of retaining clip perhaps,
rather than
> anything functional. Am I right, or should I be concerned?
> >
> > The brown between the ferrite core and the white coil housing is normal
> used in the flyback manufacture.
> >
> > However, the rust on the metal clip holding the ferrite core together is
> definitely unusual - I've never seen this before.  Obviously a sign of
moisture at
> some point in its history.  Is there any other signs of moisture?  The
clip itself is
> purely mechanical (holding the two parts of the ferrite core together) and
> serves no electrical purpose.  As long as it's still structurally sound,
it's probably
> ok.
> I have actually seen a lot of this, particularly on VT220 I have restored.
> By the looks of yours, I'd say the clip is toast.
> It does hold the core together so if it comes apart and there's later
vibration of
> significance, the core might come apart and then you don't have a flyback
> anymore.
> I would try to clean up the particles that remain as they are conductive
and if
> they migrate into other parts of the circuit or if the remains of the clip
> off and end up somewhere else in the circuit, you'll have a lot more to

Indeed, I intend to clean up the area as there are some rust particles
around there.

> I have repaired several flybacks with this problem by removing them from
> board, removing the rusted clip and all the gunk and then threading a #12
> #14 insulated copper wire through the core and around the ferrite and then
> twisting it back on itself to cinch it up.
> You might also be able to accomplish similar without removing the flyback
> from the board if you can get your cinch wire underneath the bottom of the
> core, between it and the PCB and then wrap it over the top.  I think the
> splits right about where most of your clip has disappeared-- about half
way up
> the side of the flyback in your photo.
> I haven't it done it this way myself but you might also be able to save it
> some epoxy or even hot melt glue if you can encapsulate both halves of the
> ferrite that way.

It looks like I can get some wire around the core halves to hold them
together, without removing the board. I will have a look at the weekend.



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