"Warm-up time" for Buchla 400?

[Chris Stecker]

Hi there,

I've got a Buchla 400 that works pretty good except for one strange deal:
it needs to "warm up" before it will boot.   What I mean is that when I
first power it on, it's in its default non-working state (unbooted), but
asking it to boot from floppy, or even to run a RAM test (a procedure
stored in ROM OS memory) results in nothing.  Repeated attempts don't help.
After being left on for about 10 minutes, the machine will finally run a
RAM test, but still won't boot from floppy.  Finally, after "warming up"
for 15-20 minutes, it will load from floppy and run fine thereafter.  I can
turn it off, then back on, with no problems.  It's just that initial 20
minute period...

I've worked on several 400's, and this is the only one I've seen with this
particular problem.  There are, of course, no components that ought to need
warming up in the beast.  My thoughts are (1) something is loading one of
the supply voltages in a capacitative manner, and gets charged up in the 20
minute period (seems like a long time for that) or (2) something to do with
heat.

Anyway, I wonder if any of you had seen a problem like this before.  Thanks,

Chris Stecker