2 Mar
2009
2 Mar
'09
10:37 a.m.
The harness I have is not the same as either of the
two that someone sent me
pictures of. It is not a ribbon cable, it has discrete wires, of different
lengths, its part number is 70-20450-01, rev C1 and there is a date of 9th
Dec 1985 on it. The actual connectors though look like the connectors on the
bad ribbon cable harness, I think they are MTA-156.
AFAIK this is a side issue. While the older pawer harness can overheat
_in use_, it will not cause the PSU to fail at switch-on. In other words,
if you have the older harness, you should reuild/replace it, but this is
not the cause of your problem/
Some have suggested it blew because I had insufficient load. I had a TK50
and an RD53 attached, would that no be sufficient. Furthermore I did not
As I said earlier, I'd not use thos 2 devices as dummy loads, they are simply
too valuale for that. Get soem 6V and 12V car bulbs...
While I beleive there are SMPSUs that fail if turned on with no/insufficient
load, I've yet to meet one. I've seen supplies that trip repeatedly if
given no load. I've seen supplies (including ones from DEC) where some
of the outputs give far too _low_ a voltage if the main output is not
suffiiently loaded. But not one that fails.
actually switch the PSU on, just connected it to the
mains, would the load
connected to the PSU matter when the PSU is not actually switched on?
Hang on Are you saying the rocker switch on the front was not turned on?
In which case most of the PSU electronis was not powered. About the only
thing that could have failed in the way you descrie are the mains input
filter capacitors.
Have you opened up the PSU case yet? Can you see anything obviously
burnet or exploded? If so, what?
There was also a suggestion that the PSU would have needed switching
separately for 50Hz operation as well. The hardware manual I have for the
machine tells me how to switch between 110 and 240, but does not say
anything about switching it for frequency, so I suspect this was not an
issue here.
It isn;t. There is no frequency adjsutment on the BA23 PSU.
From the various responses I think it would be
unwise for me to attempt a
repair. Is there anyone on this list who is in the UK
who would be willing
and able to fix this PSU, or who knows someone who might be? 
2 Mar
2 Mar
4:06 p.m.
On 02/03/2009 18:37, Tony Duell wrote:
While I beleive there are SMPSUs that fail if turned
on with no/insufficient
load, I've yet to meet one.
The small switcher in DEC's TK50 tabletop box does exactly that. I got
to sort through a pallet-load of the things once, and got to keep
several that looked repairable. Well, they were, but at least two had
to be repaired twice because I forgot to hook up the minimum load board
that the TK50-AA box usually has.
However, I have to admit that's the only time I've been bitten in that
way, and the PSU in a BA23 certainly shouldn't get too upset by a
no-load situation. I'd guess it's just lost a mains filter cap.
--
Pete Peter Turnbull
Network Manager
University of York
5773
days inactive
5774
days old
1 comments
2 participants
participants (2)
-
ard＠p850ug1.demon.co.uk -
pete＠dunnington.plus.com