26 Aug
2010
26 Aug
'10
11:45 a.m.
On Wed, 25 Aug 2010, Eric Smith wrote:
That would apply to me too i nthe case of this HP terminal. I am not
depending on it working. Yes, I want to be able to use it, and I want to
play about with it, but if it fails I am quite happy to open it up and
grab the 'scope and logic analyser...
I think the way that I would state it is that
just because the system is
working correctly (at the moment) doesn't mean that it isn't broken.
Part of the reason I don't think we'd fix such a problem in the PDP-1 is
that the PDP-1 isn't doing anything criticial. We can afford to have
downtime if a latent problem eventual causes a failure. If we've
properly documented that latent problem, we can check for it when the
system does fail, and fix it if necessary at that time.
Your ability to tolerate downtime is significant, as also is your thorough documentation, so that the repair won't end up in
the hands of board
swappers.
Y'know, it would be fun to see an entire set of exhibits explicitly about
failure modes. Remember the HUH S100 boards for the TRS80, where one of
the entire early production runs was reversed, but could be used by
soldering all of the components to the back side of the board?
:-).
I am pretty sure there ws a DMM sold in the UK which sued as expensiv
'custom' 40 pin chip. Turns out it was a 7107 or something mirror-flippe.
You could use a normal one if you soldered it to the otehr side of the
PCN (and there was enough space to do that.
Sinclar machines are knwon for such bodges -- ICs and/or transistors
stuck on top of other comonents with kludgewires everywhere. Although
wether those machines ever worked correctly is debatable :-)
-tony