On Sun, May 8, 2022 at 1:02 PM Maciej W. Rozycki via cctalk <cctalk@classiccmp.org> wrote:
> In the H7821 it's -9Vdc return pairing with -9Vdc supplied on the yellow > wire (an isolated circuit). Pin numbers 14 & 13. Try measuring voltage > across the suspicious connections as any reference to ground may not be > indicative. > > This voltage is also present with the H7819 PSU. It's not clear to me > what it is used for. It's only a guess (this is rather more modern than the DEC hardware I have), but it may be a supply for a thinwire ethernet transceiver circuit. This would be insolated from system ground of course, and I've seen something similar in an X-terminal. -tony > > Maciej
