7 Sep
2014
7 Sep
'14
12:46 a.m.
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 with
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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