12 Jun
2009
12 Jun
'09
7:30 a.m.
Eric Smith wrote:
Ian King wrote:
Not sure what type of components DEC was using in these, but on the R side,
carbon-composition resistors tend to drift high with age.
I just pulled out a few-K series flip-chips ca. 1971 and made some measurements
on several dozen 10% carbon comp R. All of them were *above* target, with a
couple of them a little above tolerance (out of spec).
(An early 60's RACAL receiver I was rebuilding recently had over a third of the
resistors above tolerance.)
we just got a restored PDP-8/TC08/TU56 booting
OS/8!
Cool!
After calibrating the TC08, I turned off the
system to put all the 'skins' back in place, fired it up... and it wouldn't
boot After checking the obvious things, I decided to let the system warm up for fifteen
minutes or so. Yep, it booted fine.
Something tells me I need to look at the RC components in those one-shots and clock
circuits, and probably replace some realllllllllly old capacitors. -- Ian
I can't imagine that they would have used electrolytic capacitors in
those, and I don't think ceramics are likely to have gone bad unless
they've been subject to extreme mechanical shock. I'm not sure about
other kinds of capacitors, but I'd expect they'd most likely have used
ceramic.
I certainly wouldn't go replacing ceramic capacitors without using some
freeze spray to confirm that it is a temperature problem and identify
the failing component.