10 Apr
2013
10 Apr
'13
2:09 p.m.
Started tearing into the 11/780 and pulled the 11/03 and the RX01 out
to clean and test. Looks like the PS is bad in the 11/03. It powers on
and the fans run because they are AC but I am getting sometimes 4.5
volts on the 5v line and 0 volts on the 12v. I have 34 volts coming out
of the diode rectifier. I suspect switching transistors.
Anyone have experience with these?
Probably not that particualr PSU, but I know that some of the smaller DEC
pSUs used on Qbus systems do not work correctly unloaded. But the normal
behaviour then is for the 5V rail to come up but the +/-12V rails to be
very low -- they 'tag along' with the 5V rail so if the latter is not
loarded the PSU is running at very low power, the choppers are on for
very little time so the 12V liens don't come up.
I would try loading the 5V line (a 6V 12W bulb should do it) and see what
happens.
-tony