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From: info-vax@ucbvax.UUCP
Newsgroups: mod.computers.vax
Subject: Re: Re:  Max amps in a 750 (summary)
Message-ID: <8512140537.AA01864@lc.garage.packard.DK>
Date: Sat, 14-Dec-85 00:37:07 EST
Article-I.D.: lc.8512140537.AA01864
Posted: Sat Dec 14 00:37:07 1985
Date-Received: Sun, 15-Dec-85 17:11:19 EST
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> Older BA11's have 25 amp power supplies, not 32.  Be sure to check yours.
> If I remember correctly, you call pull out the BA11, crawl underneath
> and look at what's written on the supply.
> 
> Rick Watson
> University of Texas Computation Center

Rick is pretty close to right with his assessment of this situation.

The amperage capabilities of the BA11 boxes (any UNIBUS i.e VAX and non-VAX)
is determined by the model number of the +5V regulator inserted in the power
system.  The "normal" BA11 can hold two +5V regulators, which can be 
either/or/or both:

		1.) H741 = +5V @25 AMPS
		2.) H7441 = +5V @32 AMPS.

The configuration is determined by the model number of the BA11 box itself
at order time.  The H765 Power System (which is mounted in the BA11-K box
and contains these regulators) is the real determining factor, for example:

		1.) H765-A has two H744 regulators.
		2.) H765-H has two H7441 regulators.

and:

		1.) BA11-KE has an H765-A.
		2.) BA11-KA can be ordered with either a H765 -A or -H.
		3.) ad nauseum.

To make this even more fun, DEC Field Circus can change any of these 
configurations at repair, install, or PM time depending on parts 
availability or the power requirements of the UNIBUS devices being
installed or serviced within a particular DD11 (SPC) or device unique
backplane being powered by THAT +5V regulator.

(Do you think DEC does all this to confuse the Russians?)


Getting back to Rick's observation:

To determine what the power capability of your BA11 box is currently:

	1.) Look at Regulator 2 & 3 (numbered from right to left)
	2.) If both are H744, then BA11 box = +5V @25 AMPS.
	3.) If both are H7441, then BA11 box = +5V @32 AMPS.
	4.) If there is one of each;
		a.) The backplanes plugged into J9 and J11 
		    have the power rating of Regulator 2.
		b.) The backplanes plugged in J3, J5, and J7
		    have the power rating of Regulator 3.

			Note: These regulator types may be determined
			      by pulling out BA11 box and viewing from
			      the bottom or swinging up the box to the
			      maintenance position.

			WARNING 1:  This procedure can bring down the 
			            operating system, so is preferably
			            done with the system down and the 
			            system powered down.

			WARNING 2:  This prodcedure can also result in
			            damage to UNUBUS and communications
			            cables, unless done properly.

CONCLUSION:  If you really have a need to know the power capabilities
             of your UNIBUS boxes, have your maintenance personnel
             do the checking for you!!	







				From the bottle of Wine,

					Ronald J. Wine

					AT&T Communications
					4200 Commerce Court
					Lisle, Ill.     60532
					N.T.S.C.        (1st Flr)
					ll1!wine