25 Nov
2015
25 Nov
'15
8:36 a.m.
On 11/25/2015 01:34 AM, Robert Jarratt wrote:
I did not use PC power supplies, I used a couple industrial
power supplies. I built this system in 1986.
But, generic PC power supplies DO have a little bit of -12 V
for serial cards. The standard PCI connector
has a -12 V pin. PCIe seems to have dropped the -12V supply.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Jon Elson
Sent: 25 November 2015 02:05
To: General at classiccmp.org; Discussion at classiccmp.org:On-Topic and Off-
Topic Posts
Subject: Re: Replacing MicroVAX II PSU With a Modern PSU
On 11/24/2015 05:52 PM, Mark Wickens wrote:
Thanks Jon. I think standard PC PSUs only do +5 and +12, so how did you do
-12? I haven't looked into this at all and I
suspect it's probably quite
tricky indeed. I did look around a while back drew a blank.
I built up a Micro-VAX II system out of boards, backplanes and assorted junk. I
made my own power supply. The power supply is actually easy, just +5 and
+12, with a touch of
-12 for serial I/O.
The only tricky thing is the power-OK and reset logic, which really wasn't all
that tricky, either.
I had a power and thermal safety control panel on it repurposed from the
original 3rd party IBM mainframe memory box that would shut it down if there
was an abnormal voltage or cooling failure.
Jon For P OK and DC OK I found this:
http://home.windstream.net/engdahl/powerup_reset_circuit.htm, but just for test purposes I
assume I could connect the +5 direct to P OK and DC OK.
BPOK needs to pulse low
after power is stable, BDCOK should
be high when power is OK. Or, at least, that's what I got
from the drawing you linked to.
Jon