27 Mar
2006
27 Mar
'06
11:49 a.m.
Okay, so I was thinking, would it be possible to replace the regulators and
whatnot in a BA11 with several standard PC power supplies? Obviously there
would be adjustments that need to be made, but considering the DEC units are
now 20+ years old and the out-of-service modules may have dried up caps,
would this not be a possible option?
I'm just curious, I'm no electrician, nor have I looked over the leads yet.
Secondly, if I have less than half the BA11 box full of cards, do I need
both of the fans plugged in?
Julian
27 Mar
27 Mar
12:15 p.m.
I haven't checked the specs, but I'd be surprised if the standard PC
supplies could put out the amps required.
Jay
12:34 p.m.
On Mon, 2006-03-27 11:15:09 -0600, Jay West <jwest at classiccmp.org> wrote:
I haven't checked the specs, but I'd be
surprised if the standard PC
supplies could put out the amps required.
Looking at
http://bitsavers.vt100.net/dec/unibus/EK-BA11A-TM-003_Aug83.pdf, the
PSU will give you these:
Logic Voltage:
+5.1V +/- 0.10V min: 6.0A max: 120.0A
+15.0V +/- 0.30V min: 0.0A max: 3.0A
-15.0V +/- 0.30V min: 0.0A max: 3.0A
+12.0V +/- 0.24V min: 0.0A max: 5.0A
Memory Voltage:
-12.0V +/- 0.24V min: 0.0A max: 1.0A
+5.1V +/- 0.10V min: 0.0A max 10.0A
Most of these shouldn't be much of a problem for a high-powered PC
power supply, except 120A for 5.1V ...
MfG, JBG
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4:03 p.m.
Wolfe, Julian wrote:
Okay, so I was thinking, would it be possible to
replace the regulators and
whatnot in a BA11 with several standard PC power supplies? Obviously there
would be adjustments that need to be made, but considering the DEC units are
now 20+ years old and the out-of-service modules may have dried up caps,
would this not be a possible option?
Certainly possible, with either OTS PC style
or switcher PS modules.
For the 'classic' DEC brick-style regulator modules as in the BA11-K box:
H744 ....... +5V @ 25A
H7441 ...... +5V @ 32A (upgrade to the H744)
H745 ...... -15V @ 10A
H754 ...... +20V @ 8A & -5V @ 1-8A
54-11086 .. +15V @ 4A
A standard BA11-K box has 2xH744 (or later 2xH7441), 1xH745, 1x54-11086, and
usually a spot for 1xH754 (for core memory, not req'd if no core).
Each of the backplanes (DD11-D/C) has one or two AMP MateNLok connectors
that
handle the power distribution to the various slots, typically a pair of 14ga
wires for +5V, and one wire each for the other voltages. Each 9slot SU is
nominally 10-15A max at +5V, easily handled by a small switcher.
The main problem I see with OTS PC supplies is they are +12V and not +15V.
Older DEC cards expect +15V input and do on-board regulation to +12V. Only
some of the later MOS memory cards (like MS11-PB 1MB for the 11/44) expect
+12V on the backplane (which is supplied directly from the BA11-A supply).
I have built a benchtop debug station that uses a DD11-CK 4 slot SU with
an inexpensive +5V at 10A, +15V at 2A, -15V at -2A modular supply. I suppose it
would be fairly straightforward to rip out the rear end of a BA11-K box
an lineup 5 or 6 of these and completely replace the power subsystem.
I'm just curious, I'm no electrician, nor have I looked over the leads yet.
Secondly, if I have less than half the BA11 box full of cards, do I need
both of the fans plugged in?
For the BA11-K box remember the fans not only cool the boards but also the
power regulators and internal power supply transformer. I would not disable
one of the fans even if the box were lightly populated. Power supplies want
to be in a cool environment, heat is your biggest enemy (besides time, I
guess).
Julian
5:35 p.m.
Okay, so I was thinking, would it be possible to replace the regulators and
whatnot in a BA11 with several standard PC power supplies? Obviously there
Firslty 'BA11' covers dozens of mounting boxes for PDP11 stuff, both
Unibus and Q-bus. And there were many different PSUs used with them
would be adjustments that need to be made, but
considering the DEC units are
now 20+ years old and the out-of-service modules may have dried up caps,
would this not be a possible option?
I fail to see why you want to do this. The DEC PSUs are conservatively
designed, well built, and properly documented. PSU PSUs are none of these
in my expserience. Most, if not all, compoents for the DEC supplies,
certainly those components that are likely to fail, are still available.
Easily availalbe.
Now, I said earlier that there were many different PSUs. Most of the
older ones used the DEC 'Bricks' or similar circuitry. While these are
switch-mode units, there are 'friendly' switch-mode units. The input is
about 25V AC from a step-down isolating transformer. There is no mains or
rectified manis around. Yes theres enough power to burn the tip off your
screwdriver if you short the wrong thing out, or to make some of the
components explode (the latter is direct experience), but it's a lot
nicer than the rectified mains in a lot of later supplies.
There are exceptions. The supply in the 11/44 is a mains voltage
(on-line) swithcer. In fact it's a particularly complicated one. This is
not a supply that I like working on, but I've done it, and lived to tell
the tale. So it is _possible_. Just be aware that there are a couple of
coke-can size capacitors at the left side that charge up to 200V each and
are in sereis. Touch the output of that (and it's on barrier strip
terminals on top of some of the PSU boards) and you won't feel anything
ever again. Seriously!
But getting back to your suggestion. It probably is possible to
substitute PC power supplies, but it would be a lot less work to simply
repair the existing supply. Once you realise it's a swticher, and once
you find out what the 723 chip really is (read the data sheet, it must be
out there somewhere) and understand op-amps, then the design of the
'brick' is not hard to follow.
Secondly, if I have less than half the BA11 box full
of cards, do I need
both of the fans plugged in?
Possibly not, but I've yet to find a computer that objects to
over-cooling... WHat's the reason for wanting to disconnect one of the fans?
-tony
6674
days inactive
6674
days old
5 comments
6 participants
participants (6)
-
ak6dn＠mindspring.com -
ard＠p850ug1.demon.co.uk -
bfranchuk＠jetnet.ab.ca -
ISC277＠CLCILLINOIS.EDU -
jbglaw＠lug-owl.de -
jwest＠classiccmp.org