11 Nov
1997
11 Nov
'97
11:08 a.m.
Alright. It wasn't powering on because I left J3 unplugged.
When I plug in J5 (4-wire plug on the line power module) everything goes.
I can plug in everything else, and all I get is a relay click.
I found the easy way to play with these plugs is to set the BA11
upside-down on the table, and unmount the PSU so I can get access.
What is J5 for and what voltages are supposed to be there?
I have an oscope here, and I may be able to dig out a VOM...
It's obvious I switched wires or something in the line power module.
Visual inspection shows nothing obviously wrong...
11 Nov
11 Nov
11:31 a.m.
On Tue, 11 Nov 1997, Daniel A. Seagraves wrote:
Alright. It wasn't powering on because I left J3
unplugged.
When I plug in J5 (4-wire plug on the line power module) everything goes.
I can plug in everything else, and all I get is a relay click.
I found the easy way to play with these plugs is to set the BA11
upside-down on the table, and unmount the PSU so I can get access.
What is J5 for and what voltages are supposed to be there?
J5 carries the wires to the 2 primary winding on the mains transformer in
the PSU. On 230V units the 2 windings are linked in series, on 120V units
(like yours, I guess), in parallel.
With J5 unplugged, the PSU isn't going to do anything. The only bit of
circuitry that is then powered up is the little PSU that operates the main
relay in the control chassis.
The fact that the breaker trips when the transformer is plugged in doesn't
tell us much (other than there's something wrong in there). Obvious
problems would be :
1) A short somewhere on the secondary side (in one of the regulators,
say). This will obviously cause too high a current to flow in the primary
circuit
2) A defective mains transformer (unlikely, and pray that it's not)
3) You've reversed one of the primary windings (swapped over leads on J5).
I assume you've not fiddled with this
4) Did you fit a new breaker? The mains transformer takes a high surge
current at switch-on. The original breaker was a time-delay one - is the
new one of a similar type.
What happens if you remove all the loads from the secondary of the
transformer (pull out the 8-pin plug from the distibution pcb that carries
8 black wires, and unplug the edge connector from the 15V PCB in the PSU)?
Will the breaker hold then with J5 in place?
Did you get my earlier message about section-isolating this fault? I have
the BA11-K prints at home, and can talk you through the entire PSU if
necessary, but at least let's try to find out which bit is faulty.
I have an oscope here, and I may be able to dig out a
VOM...
It's obvious I switched wires or something in the line power module.
What did you disconnect? If you think you may have swapped wires, let us
know what you fiddled with _now_ rather than later...
Visual inspection shows nothing obviously wrong...
-tony
11:42 a.m.
On Tue, 11 Nov 1997, Tony Duell wrote:
J5 carries the wires to the 2 primary winding on the
mains transformer in
the PSU. On 230V units the 2 windings are linked in series, on 120V units
(like yours, I guess), in parallel.
Okay, that big transformer in the top of the PSU?
With J5 unplugged, the PSU isn't going to do
anything. The only bit of
circuitry that is then powered up is the little PSU that operates the main
relay in the control chassis.
Okay.
The fact that the breaker trips when the transformer
is plugged in doesn't
tell us much (other than there's something wrong in there). Obvious
problems would be :
1) A short somewhere on the secondary side (in one of
the regulators,
say). This will obviously cause too high a current to flow in the primary
circuit
How do I check that? I've never played with voltages over 24V before.
2) A defective mains transformer (unlikely, and pray
that it's not)
It probably isn't, this worked fine until I broke it.
3) You've reversed one of the primary windings
(swapped over leads on J5).
I assume you've not fiddled with this
I may have. I had to unplug the breakers to replace them.
4) Did you fit a new breaker? The mains transformer
takes a high surge
current at switch-on. The original breaker was a time-delay one - is the
new one of a similar type.
The breakers came from a VAX PS, DEC model # 70-18763-00
What happens if you remove all the loads from the
secondary of the
transformer (pull out the 8-pin plug from the distibution pcb that carries
8 black wires, and unplug the edge connector from the 15V PCB in the PSU)?
Will the breaker hold then with J5 in place?
I'll check that.
Did you get my earlier message about section-isolating
this fault? I have
the BA11-K prints at home, and can talk you through the entire PSU if
necessary, but at least let's try to find out which bit is faulty.
Hmm. My boss used to work on big PSUs in CB radio linears, if you could
scan the schematic or something he could troubleshoot this...
What did you disconnect? If you think you may have
swapped wires, let us
know what you fiddled with _now_ rather than later...
I detached the 4 wires attached to the breakers.
I detached the 2 line wires last so as to not swap them, but I may have
anyway.
11:51 a.m.
On Tue, 11 Nov 1997, Tony Duell wrote:
> What happens if you remove all the loads from the
secondary of the
> transformer (pull out the 8-pin plug from the distibution pcb that carries
> 8 black wires, and unplug the edge connector from the 15V PCB in the PSU)?
> Will the breaker hold then with J5 in place?
Yes. It comes up, and the fans spin up. With just the edge connector
off, it pops. With just the edge connector on, it goes.
12:12 p.m.
On Tue, 11 Nov 1997, Daniel A. Seagraves wrote:
OK, so the transformer is probably OK.
What happens with :
8pin plug out, edge connector off? (breaker holds?)
8pin plug in, edge connector off?
8pin plug out, edge connector on?
If the breaker will hold with the edge connector off and everything else
in place, first check that the edge connector is the right way round, then
start debugging the (trivial) power controller card.
-tony
On Tue, 11 Nov
1997, Tony Duell wrote:
> What happens if you remove all the loads
from the secondary of the
> transformer (pull out the 8-pin plug from the distibution pcb that carries
> 8 black wires, and unplug the edge connector from the 15V PCB in the PSU)?
> Will the breaker hold then with J5 in place?
Yes. It comes up, and the fans spin up. With just the edge connector
off, it pops. With just the edge connector on, it goes. 
11:57 a.m.
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11:57 a.m.
On Tue, 11 Nov 1997, Tim Shoppa wrote:
What sort of VAX PS is that? Is it a similar BA-11 type box, or
is it from something completely different (i.e. BA23/BA123?) As
Tony points out, if you got it from a very different sort of box,
it's probably not a time-delay one.
It's nowhere similar. It was 3 breakers wide, I removed the middle one.
It looks like the power controller at the bottom of the rack.
12:09 p.m.
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12:13 p.m.
On Tue, 11 Nov 1997, Tim Shoppa wrote:
What's the Amp rating? (Should be prominently
displayed
on the breaker itself).
Ahhh.... 15 for one and 1.5 for the other... that's it.
I must have misplaced that decimal.. that was stupid.
What was the problem with using the original
11/34A's breaker? Sure,
the handles are broken off, but this isn't a major problem. You
can still just push both poles into the "on" position, and if there
is an overload they're still ganged to go off together.
One looks usable, the other has parts of the switch bouncing around
inside. If I took it apart, I might be able to fix it up...
12:19 p.m.
On Tue, 11 Nov 1997, Tim Shoppa wrote:
A clamp-on AC ammeter is one choice - and its something that everyone
with minicomputers should own or be able to borrow :-). You can buy them at
Radio Shack, among other places.
That reminds me... I really must start seriously looking for a Tektronix
current probe for my 'scope.
A series light bulb is another trick. With all the loads removed from the
outputs of the regulators, the PSU shoulds run with (say) a 200W light
bulb (or enough smaller ones in parallel to equal this). The bulb should
be dim/out. If it's glowing brightly you can be sure that there's a short
somewhere.
This trick is more use on SMPS's where faults don't just trip the
breaker/fuse, they also blow expensive chopper transistors. I never power
up a repaired SMPS without some kind of limiting...
[...]
1) A short somewhere on the secondary side (in one of
the regulators,
say). This will obviously cause too high a current to flow in the primary
circuit
How do I check that? I've never played with voltages over 24V before. It also won't hurt to do a continuity check on the
breaker. If the
connections aren't what you think they are, you've got a problem!
Unless it's one of those breakers with a separate connection for the trip
element (used in the RX01/RX02 I believe), I can't see how misconnecting
the breaker will cause it to trip only when the load is plugged in.
Tim.
-tony
12:09 p.m.
On Tue, 11 Nov 1997, Daniel A. Seagraves wrote:
That's the one, yes. It's rated at somewhere near 1000VA, and has 5
separate 20-30V secondary windings - one for each of the 4 regulators, one
for the 15V board (+15V, line clock, ACLO, DCLO signals).
Well, start off by unplugging all the loads from the secondary side, as I
described below. Then add them back one at a time (see the message I sent
out this morning, if it's got to you, if not I'll send you a private
copy), and see which regulator trips the breaker. Then we need to get into
that.
Mind you, the regulators contain their own fuses, so most faults in them
only blow the internal fuse and don't trip the main breaker.
Unless you removed individual wires from J5, I fail to see how you'd have
got them back in the wrong order.
Wait a second...
Breaker_s_??? The original 11/34 breaker is a double-pole unit designed so
that if either side trips both get turned off. Have you fitted 2
single-pole breakers in place of it? That would violate the regulations at
least (the breaker in the grounded side of the mains could trip, leaving
the entire input side to the PSU live, for example).
These breakers are made in many different ratings, and with several
time-delay characteristics. DEC used many of them - not all PSUs take the
same current from the mains, and IIRC the BA11-K PSU takes a heck of a
switch-on surge - later SMPS's have inrush current limiter circuits, and
probably use different breakers
It sounds to me as though you've fitted the wrong breaker - that is all.
Do you want me to try and find the spec of the original one? I could
certainly find out what the 240V one was.
I'm guessing now, but I think the original one was a 10A, double pole,
time delay unit. What does it say on your replacement(s)?
There's no way that getting any of that wrong would cause the PSU to trip
only when the transformer was connected. Just about the only thing you
could have got wrong would have been to connect the 2 input wires to the 2
terminals on one pole of the breaker, in which case the breaker would have
shorted out the mains and would have tripped instantly when you plugged it
in.
I suspect the only problem is that you are using the wrong breaker.
-tony
J5 carries the
wires to the 2 primary winding on the mains transformer in
the PSU. On 230V units the 2 windings are linked in series, on 120V units
(like yours, I guess), in parallel.
Okay, that big transformer in the top of the PSU? 1) A short
somewhere on the secondary side (in one of the regulators,
say). This will obviously cause too high a current to flow in the primary
circuit
How do I check that? I've never played with voltages over 24V before.
3) You've
reversed one of the primary windings (swapped over leads on J5).
I assume you've not fiddled with this
I may have. I had to unplug the breakers to replace them. 4) Did you fit a new breaker? The mains
transformer takes a high surge
current at switch-on. The original breaker was a time-delay one - is the
new one of a similar type.
The breakers came from a VAX PS, DEC model # 70-18763-00 Hmm. My boss used to work on big PSUs in CB radio
linears, if you could
scan the schematic or something he could troubleshoot this...
The schematic for this PSU is probably about 10-20 A3 (11"*17") sheets.
It's not that complicated, but there's a lot of it. Let's find out what
bits you need first.
The input circuitry is very straightforward, though. Mains comes in. It
goes to the breaker, then to a mains filter. The output of that goes to
the big contactor relay. That applies mains to the input of the
transformer. The output of the transformer goes to the regulator blocks.
What did you disconnect? If you think you may
have swapped wires, let us
know what you fiddled with _now_ rather than later...
I detached the 4 wires attached to the breakers.
I detached the 2 line wires last so as to not swap them, but I may have
anyway.
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9919
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10 comments
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ard＠odin.phy.bris.ac.uk -
dseagrav＠bsdserver.tek-star.net -
shoppa＠alph02.triumf.ca