On Tue, 9 Jun 2020, Bill Gunshannon via cctalk wrote: > > For the VXT-2000 with an H7109-B the rated voltage and current values > > are printed right on the power supply label: > > > > +5.1V, 7.81A > > +12.1V, 0.62A > > -12.1V, 0.46A > > -9V, 0.2A > > > > Fixed width character pinout diagram: > > > > +=================+ > > -9V | Yellow | Orange | +12.1V > > +--------+--------+ > > ??? | White | Black | Gnd > > +--------+--------+ > > +5.1V | Red | Blue | -12.1V > > +--------+--------+ > > +5.1V | Red | Black | Gnd > > +--------+--------+ > > Gnd | Black | Black | Gnd > > +=================+ > > > > The mystery is the White wire. The power supply label only lists 4 > > output voltages. The White wire appears to be routed to the Ethernet > > daughter board. The measured voltage appears that it might be floating > > slightly negative, somewhere around -1.5V when the Ethernet daughter > > board is installed and around -5V when it is removed. Maybe it is a > > high impedance earth ground connection? It appears to be connected to > > the shield of the Ethernet BNC, which measures around 1M-Ohm to the > > chassis ground when the power supply is disconnected from the main > > board, and around 0.75M-Ohm when the power supply is connected. > > > > > Thank you for that. Mine has no labels or anything. It is PC Board > with Digital, Side 1, Side 2 and a number I don't recognize on it. > I guess the -9V is the only odd one but you could easily get that > from a -12V line. I may get to fix it yet.
For the unlabeled white wire this must be -9V return, such as say with the H7109-AA PSU used with the VAXstation 4000 VLC, the H7819-AA used with VAXstation 4000 60/90/etc. and storage expansions or the H7821-00 PSU used with several systems, where the -9V supply circuit is isolated and used, I believe, for serial line drivers/receivers. It might be worth checking. Maciej