> On Sat, Sep 30, 2017 at 6:33 PM, Aaron Jackson via cctalk > <cctalk@classiccmp.org> wrote: >> Hi all, >> >> Instead of jumping straight in and ordering an SLU, I decided to check >> the power supply voltages. My +12V rail appears to be only giving about >> +4.6V > > That does not sound fine.
I mean the 5V rail seems fine. >> This is an 11/23+ chassis and the power supply seems very large > > What type of box? BA23? BA11-M? BA11-N? You said "11/23+" which > could easily be a BA23, but it's not a guarantee. It's a H7861 power supply. > In particular I ask because I'm sifting through a pile of DEC Qbus > backplane and PSU assemblies for, I think, a BA11-M, and these have > two PSU modules, one that takes in mains and provides +5V for the > backplane, then a smaller board that taps two cables off the main PSU > and provides +12V and -12V. Both of these bolt down to a common > mounting bracket and have to be removed as a pair then each unit can > be removed from that. The other Qbus supplies I have worked with are > single-unit affairs. I had a proper look tonight and traced it back to Q3 (an MJE15030). The input is about 80V and the output is 4.4V (the same as the output). Looking at the emitter on the scope I can see that it outputs the ~4V with a bit of "vibration" which fades away very quickly. I've ordered a replacement so we will see if it fixes it. > Any sort of Hxxx number you can find would be most illuminating. > > -ethan Thanks, Aaron. -- Aaron Jackson PhD Student, Computer Vision Laboratory, Uni of Nottingham http://aaronsplace.co.uk
