Conference netcad::hub_mgnt

3802.0. "DEChub 900 Power Supply Behaviour" by GIDDAY::STANISLAUS () Wed Aug 21 1996 03:27

	Our CSC DEChub 900 has one H7890-MA power supply in power supply 
slot 1 and one DECswitch 900EF in module slot 8 working fine. I wanted to add a
DECbridge 900MX in module solt 7. But MAM module (version 3.1) said that the
available power was only 57.5 watts, whereas the DB900MX power rating says that
it draws 67.5 watts.

	So,

	First I added another H7890-MA power supply in power supply slot 2. It
turned ON alright and both LEDs on this power supply came ON. But the bottom
LED on the H7890-MA in power supply slot 1 turned OFF immediately. The DS900EF
in slot 8 continued to work OK. The MAM still said only 57.5 watts available. I
expected it to say 57.5 + 140 = 197.5 watts available.

	
	Hence when I put the DB900MX in slot 7, it turns ON, runs and passes
self-test and then very soon turns OFF. The MAM says NO POWER.

	Anyway I removed the power supply I added in power supply slot 2. Then
the power supply in power supply slot 1 immediately turned ON, it's bottom LED.

	Could this be due to a faulty MAM or a faulty power supply backplane or
a below latest rev MAM F/W ? I removed the H7890-MA from power supply slot 2 and
tried the same in power supply slot 3 or 4. Still same problem as above.

	I know the power supply is good, because it behaves the way I expect it
to behave in our LAB DEChub 900. But our LAB DEchub 900's MAM module is F/W
version 4.2.0. Our LAB DEchub 900 has 2 x H7890-MA and the MAM says available
power is 15 watts. When I put the extra H7890-MA the MAM says available power 
is 155 watts and this is the way it should behave.

Alphonse

This is almost certainly a hardware problem somewhere,
rather than firmware. The LEDs on the power supplies are
controlled by the hardware.

You might want to check the MAM's error log to see
if you are logging power supply errors. It will
probably say "DC BAD" meaning the power
supply is not doing its job.

-Mike

	I thought I should know the resolution to this problem. It was a simple
case of the ribbon cable on the MAM module not seated properly.

Alphonse