13 Apr
2009
13 Apr
'09
5:52 p.m.
I managed to get the +15V line back, and so I also have -15V. Found an
open diode and a bad power transistor. Replaced them both and it's
working again.
As ever 'A transistor protected by a fast-acting fuse will protect the
fuse by blowing first' :-)
Still no life from the CPU, but I just noticed that
ACLO and DCLO are
asserted, which I understand can cause this kind of misbehavior. (This
was happening before I broke the +15V line, I just didn't realize that
Those signals are generated on that PCB where the +15V regulator is. It's
a fairly simple circuit, it's not hard to debug.
ACLO & DCLO are active-low signals at the time
when I was testing out
the supply...) Guess I get to pull the supply again and do some more
debugging :). Is there a quick 'n dirty way to fake out/bypass these
signals so I can at least see if the CPU runs at all?
If you disconnect the wries between the PSU and the backplane (just
remove the pins from one of the mate-n-lock connectors, but rememerb
where they go!), the signals will be pulled high by the Unibus
terminator. I don't know if everything will initialise properly in that
case (I think it should do), but at least the CPU will do soemthing.
-tony