18 Mar
2005
18 Mar
'05
4:02 p.m.
Jim wrote:
I don't, but I think it's lower than that. 50kHz?
after a few days frustration, I have got a little
further with my 11/45.
The power supplies checked out OK with respect to ripple and output, but a
couple have them have the odd VERY fast spike on them - is this normal?
(I'm using a 100MHz 'scope - I suspect they may not be visible on a
They are switching power supplies, so there will be some high frequency
noise. I'm not sure what the typical switching frequency is, though I'd
guess that it would be in the 100-200 KHz range; maybe Tony Duell knows. Anyhow, one would expect some very high frequency
spikes occurring at
the interval of the switching frequency. But the spikes shouldn't have
very high amplitude; if they do, it's possible that you have some bad
filter capacitors.
I would suspsect the output filter capacitors. If those go high ESR, yuo
will get spikes on the output, maybe even enough to trip the crowbar.
Oh, and WRT the UDC card. IIRC, there are at least 2 revisions, and
there's a backplane mod you have to do (adding another clock signal) if
you replace an early one with a late one. Personally, I'd stick with the
card I know has worked in that machine, and change the defective chip.
-tony