VAX 11/750 power supply fault

Date: Thu, 29 Nov 2007 12:02:05 -0700> From: oldcpu2 at rogerwilco.org> To: > Subject: Re: VAX 11/750 power supply fault> > Simon Fryer wrote:> > Firstly, no smoke after power on, you have to be happy about that, and> > at least some life!> > > > Yes, I am quite pleased about this as well! Especially since I > completely disassembled both power supplies for cleanup. In fact, a > couple of the PS PCBs went through the dishwasher to clean up the > remains to 'rodent residue'. On the whole, it seems that I got them > back together properly! ;)> > > If you have a reasonably accurate voltmeter of sorts, what are the> > actual voltages the power supply is producing? So far it is not clear> > if the fault is with the voltage generation or detection circuits in> > the power supplies.> > > > Valid points. What I see at the 2.5V output terminals on the PS itself > is a moving target. There's a cycle of sorts. First I see about 1.5V > that climbs up through 1.6, 1.7, on up to about 2.0V over a period of > seconds. The the voltage looks like it drops to 0V momentarily, then > back to 1.5V and the cycle repeats.> > BTW, I'm using a little digital meter, so it's hard to tell what's > happening when with all the digits changing. On second thought, I do > have an old analog VOM I'll dig out and see if that confirms what I > think I'm seeing on the digital. I didn't determined if this is > synchronous with the LED pattern I see, but it probably is...I'll look > tonight. > > - Jared