* On Fri, Apr 08, 2016 at 02:33:25PM -0400, Mouse <mouse at Rodents-Montreal.ORG>
wrote:
Today, for
whatever reason, my Variac was turned down to 110V, and I
didn't notice. I turned on the ADM 3a, and... it's fine. [...]
Fascinating!
I have trouble imagining what sort of fault could cause those symptoms.
I would have agreed with whoever (tony, I think) said that if you have
HV then the horizontal scan is almost certainly operating in some
sense, but this makes me doubt that. I have trouble coming up with a
failure mode in that design that could kill the horizontal scan but not
the HV based on the power supply input voltage, so there is probably
something very unusual in there.
It IS odd.
One more observation: Two of the three +5V regulators cut out
when their input voltage exceeds about 11.5V. The input voltage
comes from a 9.4VAC winding on the primary transformer. Input ripple
is VERY low, maybe 200mV. So, I suspect those regulators need to be
replaced.
I'm sure it needs to be recapped, too, so I'll do that before I
investigate too much furtther.
-Seth
--
Seth Morabito
seth at
loomcom.com