34A Power Trouble. I calmed down, here's the facts...

From: Tony Duell <ard_at_odin.phy.bris.ac.uk>
Date: Tue Nov 11 11:31:21 1997

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

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...

Received on Tue Nov 11 1997 - 11:31:21 GMT

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