18 Jan
2012
18 Jan
'12
5:34 p.m.
On 1/15/12 9:09 AM, "Michael Thompson" <michael.99.thompson at gmail.com>
wrote:
We reformed the capacitors in all three power supplies
in the PDP-8/I
Don't "reform" them, replace them. See, e.g.,
http://www.cde.com/tech/reliability.pdf on the limitations of lifespan of
aluminum electrolytic capacitors. Keep in mind that the electrolytics in
a PDP-8/I are at least 40+ years old.
at the RICM and powered on the CPU to see if it would
show any signs
of life. It randomly lit some lights and would not react to the front
panel switches. Looks like we have some debugging to do.
Again, be sure your power supplies are in good shape, not only in terms of
static voltage but also ripple - put a scope on them under load. Some
folks don't have an oscilloscope (although I would assume you at RICM do):
for those reading along, keep in mind it's not necessary to have a 500MHz
dual-trace digital phosphor "video game" if you're working on PDP-8's
and
such. A simple 10MHz scope that should be available for under $50 (I sold
one a couple of years back for $20) is perfectly good for not only
measuring power supply ripple but for lots of other diagnostic purposes in
machines of this vintage. (I have a vacuum-tube Tektronix 561A that I
love to use for things like this, just because I can.)
The front panel power switch was corroded and burned. Any idea where
we can get a replacement?
Were can we get some Oshinos OL-1 bulbs to repair the front panel?
Does anyone have diagnostics for the 8/I on DECtape?
I'd recommend finding paper tape images (Bitsavers, pdp8online.com) and
feeding them in through a terminal emulator. The DECtape controller is
itself a complex piece of equipment - minimize your variables! :-) Once
you have the CPU running reliably, then you'll probably need to align the
(presumably) TC08 - it has a handful of trimmers that adjust various pulse
widths, and I can tell you from experience they aren't just for show.
(You'll need a scope for this, too.) -- Ian