ADM-3A question

[Anders Nelson]

I hope this thread will be written to a blog post? Lots of good info here!

--
Anders Nelson

+1 (517) 775-6129

www.erogear.com


On Wed, Aug 14, 2019 at 10:25 AM Charles via cctalk <cctalk at classiccmp.org>
wrote:

> Thanks. I believe you are right also :)
> The expensive ceramic packages have hermetic seals, not so the plastic
> (epoxy) packages used in commercial grade parts.
>
> There are some kind of failures that can be fixed by baking - but I don't
> know if this is one of them (if the bond wire is soldered to the die it
> might work). If it detached from the weld at the lead frame, no go. Anyway
> there are over 100 chips on the ADM-3A board and I would be more worried
> about damaging the others with heat.
> I just paid 71 cents for another LS193 ;)
>
> Charles
> WB3JOK/0
>
> -----Original Message-----
> From: Dave Wade
> Sent: Wednesday, August 14, 2019 5:02 AM
> To: 'Charles' ; 'General Discussion: On-Topic and Off-Topic Posts'
> Subject: RE: ADM-3A question
>
> Charles,
>
> I believe that TTL chips suffer from failure or detachment of the bonding
> wire that runs from the die to the interconnect pin, which would result in
> a
> floating pin as described.]
> Not sure if environmental storage affects this as chips should be sealed...
>
> I have also recently seen it suggested that heating the chip up in an oven
> could affect a temporary repair (sorry I can't find the reference now).
>
> Dave
> G4UGM
>
> > -----Original Message-----
> > From: cctalk <cctalk-bounces at classiccmp.org> On Behalf Of Charles via
> cctalk
> > Sent: 14 August 2019 00:20
> > To: cctalk digest <cctalk at classiccmp.org>
> > Subject: Re: ADM-3A question
> >
> > After hanging vertically for 36 hrs in a hot upstairs room, more goop
> seeped
> > out from under the keyboard. It now works again. Whew.
> >
> > While running on the bench for burn-in testing, a cursor problem suddenly
> > appeared... it would only move every other keystroke. With the technical
> > description and schematic at hand, it wasn't hard to track down a 74LS193
> > up/down counter with a blown (floating) LSB output. Confirmed by manually
> > toggling that bit and the cursor would move back and forth one position.
> > Meanwhile I removed the bad chip and put in a DIP socket. Naturally my
> TTL
> > collection didn't have an 'LS193 so I'm waiting on that. So I have a 24
> line, 1
> > column terminal :)
> >
> > The monitor was occasionally intermittent (no display at all, no HV, +15
> and
> > drive signals OK). It seemed to change with movement of the wiring
> harness
> > from the main board to the monitor, too. I reseated the edge connector on
> its
> > PCB and it seemed to be fixed - but then the VERTICAL deflection
> collapsed
> and
> > tweaking the height adjustment caused increasing loss. The 100 ohm pot to
> the
> > base of the vertical output transistor had picked that moment to go open.
> > Changed that out and readjusted everything - so far so good after another
> hour
> > of run time.
> >
> > This ADM-3A could have been unpowered (and in a storage area without
> > climate
> > control) for a very long time. I wonder if that contributed to the
> failures I'm
> > seeing... hope there aren't any more until I get to use it for a while on
> my PDP-
> > 8/A (or 11/23+).
> >
> >
> > ---
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>