On Mon, Jun 26, 2023 at 3:38 PM Jan-Benedict Glaw via cctalk
<cctalk(a)classiccmp.org> wrote:
Hi!
As I'm preparing to setup my old hardware, I fetched two VAXstations
(4000/90 and /96) from storage and cleaned one of them throughoutly.
Then I gave power (to both of them), but both won't really start:
all 8 diag LEDs are on (--> power available but CPU didn't start
executing instructions.)
I took the PSU (from the cleaned /90), a DEC H7819-AA, and measured
it. Unfortunately I didn't find pinouts or schematics at a first
search. The plate states that there should be 3.3V, 5V, 12V, -12V and
-9V. I found most of that:
+------------------------------------------------------------------+
| o |
| DEC H7819-AA PSU 10 +---+ 1 |
| (view at the bottom side) | | |
| | | |
| | | |
| 18 +---+ 9 |
| o |
| +-------+ +-------+ |
| | Fan | | Fan | |
+----------------+-------+----+-------+----------------------------+
With above pin numbering, this is what I could find / measure / deduce:
3V3 brown 10 1 blue 12V
3V3 brown 11 2 black GND
GND black 12 3 red 5V
GND black 13 4 red 5V
GND black 14 5 black GND
5V red 15 6 black GND
5V red 16 7 white -12V
5V red 17 8 blue (0.78V)
(4.91V) lilac 18 9 brown (-1.65V)
Most values look plausible, except those three in parentheses. At
least one of them should probably be -9V wrt. GND I guess, but that's
totally absent. And what's the other two? (If I got the colors wrong:
Please forgive, I'm red-green blind.) That could be some "power-okay"
indicator, or external switch-off?
I don't know this machine at all (too modern :-)) but that -9V sounds
at thought it might be for an internal ethernet transceiver. Now an
ethernet transceiver is supposed to be isolated from ground and one
way of helping with that is to have a totally isolated 9V output on
the power supply with its own 'ground', not connected to the ground
for the rest of the supplies.
Using a high impedence voltmeter like most DMMs, you'd see random
noise voltages on those 2 lines wrt the normal ground.
What voltage do you measure between the suspect blue and brown wires?
Connect your meter between them, not to the black ground and something
else.
-tony
'There is no such thing as ground' -- Don Vonada