7 Sep
2014
7 Sep
'14
10:59 a.m.
Related to the issue on corrosion on the pins I can not see any such
problem in this HP9810 I am working with. There is very little black oxide
on the TI chips with silver plated pins and nothing on the other pins. So
it is not obvious to me that it has been exposed to a bad climate. But
still, chips have failed. The PDP-11/04 dated around 1976 and the HP9830,
same vintage, I worked with earlier had only a few failed chips in the
entire machine.
Now the count is 6 NS chips and one Signetics chip. A very annoying N8885
chip has failed. A quad input NOR which unfortunately doesn't have the same
pinout as the 7402. Maybe it is similar to the 7436 which is supposed be
the same as 7402 but different pin config. Didn't find the data sheet
though.
From now on every NS chip is a suspect...
2014-09-07 16:46 GMT+02:00 Sean Caron <scaron at umich.edu>:
Wow.. yeah... that's what I'd like to avoid;
replacing hundreds of 7400
series TTL ICs... If I really had to replace them, I could probably get the
job down into the double-digit numbers of IC replacements by just reducing
the switch configuration a little bit...
Thanks for posting the link to the page about the logic analyzer from the
DDR. I'm very much enjoying reading it now. I always get a huge kick out of
seeing how they did things behind the iron curtain (though I'll keep my HP
1662A, thanks!)
I wonder if there is much of a computer collecting community in the former
Eastern Bloc and, if so, how successful they have been in preserving
historical items from the Cold War era. Eastern Bloc engineers tried some
very interesting stuff over there in isolation from the "mainstream" in the
West... ternary logic, hybrid analog/digital CPUs, VLIW - before we ever
saw that "over here", etc.
I think some of this was an attempt to make up for trailing in process
technology and assembly quality with architectural cleverness (although as
Intel well demonstrates, he with the best process technology always wins in
the long run, architecture be damned, LOL), some was maybe just straight-up
old time engineering creativity at work. It's neat to see what people come
up with when they're a bit removed from the "prevailing knowledge"
(although there was certainly PLENTY of straight cloning of Western designs
being done as well).
Best,
Sean
On Sun, Sep 7, 2014 at 3:46 AM, Holm Tiffe <holm at freibergnet.de> wrote:
with
Mattis Lind wrote:
> After the successful restore of the HP9830B I continued with the
HP9810A
> that I was able to get from the Swedish
Maritime Administration. (
> http://www.datormuseum.se/computers/hewlett-packard/hp9810a )
>
> The machine has been sitting in a storage container for many years
until
I
> was able to rescue it. And of course it was dead. Testing the CPU
boards
in
> the working 9830 gave that three out of four boards were faulty.
>
> This far I have replaced four TTL chips. Three on the clock board and
one
> on the ALU board and all of them are made by
National Semiconductor,
date
codes are
mid 1972. All are plastic DIP. The failure mode seems to be
that
the outputs are floating. I guess that the
bonding wires are broken.
Can it be that the moisture in the storage container that has made it
into
the chips corroding the wires?
What is the experience when it comes to different manufacturer and
plastic
DIP TTL? Which are better, which are worse after
40 years?
Not exactly an answer to your question but I have similar experiences russian chips made before 1990.
I've reapaired an GDR made Logic Analyzer calles MC80-LA in the past,
(http://www.robotrontechnik.de/index.htm?/html/computer/la.htm)
it wasn't muchg effort to repair the first fault, an russian K155LA3
(7400)
on the video board was broken. After this the
machine was working...for a
short time. In the next following 2 weeks I had to replace approx. 60 (!)
broken russian TTL chips with exactly the same fault, floating outputs.
(relativley easy to find if you can just test the output Levels with an
scope or a TTL-Level probe).
Russian chips in ceramics don't had this problem, they where and still
are
a live, only the chips in dark green or brown
plasitcs where affected.
the chips died like popcorn...., I think that has todo with some moisture
in the plastic enclosure of the chips. Maybe they where still alive whn I
had dryed them in an oven before applying power to them?
Regards,
Holm
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