Re: 7d01 with df1 garbled display

Miroslav Pokorni
 

Hello Zenith,

Yes, you are absolutely right. Those low-pressure tin-to-tin contacts tend
to fail over time due to oxidation. It is only 'gas tight' and noble metal
contacts that make reliable sockets. I do not quite understand how a
combination of tin plate and gold works, but it does. Over past twenty years
there were number of attacks on tin plate to gold contact, about every four
to five years and then it turns out that arguments are short on substance
and whole thing gets dropped quietly. Usually, argument runs that gold and
tin in contact would cause fretting corrosion of tin. The last three
instances that story was flogged, it came out of AMP, I guess someone in
their metallurgical department is pursuing the line of fretting corrosion.
Is it not funny that AMP is one of few companies that have been pushing for
tin plated edge connectors? The last instance of gold to tin controversy
that I know of was around 1997 or 98, when Intel issued statement that
warranty on their motherboards was void if gold plated SIMMs were used in
it. I was working for a memory company and we had to contend with it,
because there were customers who would demand gold plating and then others
who were heeding Intel's edict. We requested supporting documentation from
Intel and sure enough, they sent us an article published by an AMP's
metallurgist. Knowing that it was just another tack of an old theme, company
decided to disregard Intel's notice and prepared a letter for customers who
expressed concern, explaining the previous history and seesaw of tin to
noble metal contact. Intel's notice was on their web site and their
marketing was aggressively pursuing the matter through trade magazines, but
after couple of months whole thing was quietly dropped. The first hint was
that notice was removed from web site.

As for flat cable, would you please describe that connector and cable more
closely so that we can identify it. I am guessing that brand was Spectra
Strip, a division of Amphenol: connector was black body and cable was color
coded; I believe that Spectra Strip had color coding of flat cable
trademarked, because no one else was using that for quite long time, just
about right timing for trade mark to expire. Spectra Strip thought that they
were smarter than rest of the bunch and they just about sunk because of it;
good thing was that Amphenol was doing real well and could cart them for
awhile.
Gold price of $800/oz brought grief to all of us and Insulation Displacement
Connectors (IDC) seem to have been hit harder then others. Their problem was
that cable part of connector did not have enough strength to live through
insulation displacement and still exert enough pressure to form gas tight
contact. The T & B made a name in IDCs, and I hope fortune, with their tulip
contact. The insulation displacement part of that contact looked like the
tulip flower, with four edges pressing into the wire and it relied solely on
metal to exert pressure on wire, unlike other connectors (Spectra Strip, 3M,
Berg) which relied on plastic body to support cutting edges of contacts. In
first iteration, all those other companies changed contact to have four
points to cut into wire, but cutting surfaces were highly cantilevered, so
not enough force was supplied by metal. It was the next iteration when all
of them got it right and it was only rarely, when someone tried to re-use
connector or did not use right tool for assembly, that problem reappeared. I
guess, since that time there were always batches when material was not quite
right, like GM putting out a batch of cars with gear in transmission which
skipped heat treating.

I guess, in this instance you can not blame Tektronix accountants for trying
to unreasonably pinch few pennies, not that I would put that past them. The
whole IDC industry went to selective gold plating, whatever marketing name
they gave to it, so getting full gold plating without custom order was just
not possible ever since it became clear that gold price was to stay high.

Regards

Miroslav Pokorni

----- Original Message -----
From: "zenith5106" <zenith@...>
To: "Miroslav Pokorni" <mpokorni2000@...>
Sent: Thursday, May 29, 2003 9:38 AM
Subject: Re: 7d01 with df1 garbled display


Miroslav,
I won't argue with you on that but I'm pretty sure age is also a
factor. The way the contacts were designed in combination with low
tension it was easy for dirt it enter or more likely oxide to build
up between the contacts an IC pin.
While we're at the topic there were another similar source of
intermittent faults. I guess at about the same time as the TI sockets
Tek was trying to save money on the ribbon cable connectors that were
in virtually every instruments. They used to be all gold plated but
they changed it to be goldplated only at the contact areas and the
rest of the connector had some other cheaper plating. I think the
name of the connectors were "spot on gold" or "spot of gold". They
also were susceptable to oxide building up at the point it had been
crimped to the cable. If you carefully wiggle intermittent cable you
can watch the fault come and go. A simple solution is to carefully
solder the cable to the connector. They can be identified by color,
compared to a real gold connector they were much more pale in color.
The bottom line is, if you have an intermittent instrument which
contains these sockets and/or the these ribbon cables they should be
the prime suspects.
/Zenith

--- In TekScopes@..., "Miroslav Pokorni"
<mpokorni2000@y...> wrote:
Hello Zenith,

Those sockets that you showed in picture look like famous TI
sockets that
wicked up flux and got fouled up. In most cases, they would be a
problem
from the start, on production line. Later on, TI tried to correct
problem by
placing a rectangular piece of paper of some kind at the bottom of
the
socket. The paper was pierced to let pins through and idea was that
paper
would hug outside surfaces of pin and keep flux from wicking. That
was
improvement, but was not good enough and that socket died. The AMP
had a
cheap socket, but they learned from TI's experience. Pin in AMP's
socket was
going all the way up the socket and was bent down to form one side
of
contact with IC and then was bent upward again to make the other
side of
contact. With such a pin flux would wick up the pin but could not
reach
contact area.

Regards

Miroslav Pokorni

----- Original Message -----
From: "zenith5106" <zenith@t...>
To: <TekScopes@...>
Sent: Wednesday, May 28, 2003 12:10 PM
Subject: [TekScopes] Re: 7d01 with df1 garbled display


--- In TekScopes@..., Joshua Van Tol <josh@s...>
wrote:
I've got a 7D01 with a DF1 data formatter that exhibits the
following
symptoms:

On power up, all the front panel lights come on. Sometimes most
of
them
come on and then a few seconds later the rest come on.
When the display comes up, it's all garbled. Usually a whole
screen
of
the same character.

Any ideas what this might be? I'm thinking the processor is
either
resetting, or reading incorrect data from its ROM.
---
Miroslav is right. The IC sockets on early 7D01's were really
bad. If
I remember correctly they were Texas brand and type C95. They were
installed in many Tek instruments at the time but seemed to create
the most problems in 7D01. The 7D01 problems were so severe that
Tek
even replaced several of the boards on warranty. It could be
easily
identified by its unique profile, looking at the short end. I put
a
picture at http://w1.871.telia.com/~u87138090/TexasC95.jpg if
anybody
is interested. Another problem with early 7D01's was that the
cursor
switch and position pots were very sensitve to even small static
discharge which would cause the instrument to reset when the knobs
were touched by the operator. This was later corrected with a new
type of pots with grounded shafts.
/Zenith

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