11 May
2006
11 May
'06
12:18 p.m.
Tony, responses to your statements are below, but as a general question to
those who are helping me with this, is the H745 light supposed to come on if
it's just connected to the power distribution board? i.e. am I supposed to
se a light on with no load like the H7441s do?
Wow, OK, so what is it then? This really has me stumped.
Is it still possible I have an input box problem?
-----Original Message-----
From: cctalk-bounces at classiccmp.org
[mailto:cctalk-bounces at classiccmp.org] On Behalf Of Tony Duell
Sent: Thursday, May 11, 2006 1:20 PM
To: cctalk at classiccmp.org
Subject: Re: BA11-K low AC output levels
This could explain my reading. I was only measuring one wire at a time.
Also, when I measure each of the 8 wires on P1 in sequence, one is slightly
higher than the other, alternating between the 2. Secondly, when measuring
off the power distribution board, I get the same type of reading for each
regulator, one at 15-16v, one at 10-13v
Not that it matters, but the thing that got me started on this path is that
the H745 has two pins, who each say "20-30VAC"
Okay, so, I'm back to working on my /34. I think I made
significant
progress tonight.
What's going on is, I've narrowed it down to low AC levels
coming off
the transformer. The printset and H7xx modules
specify an
incoming AC
of 20-30v (printset says specifically 28v.) All
lines
coming off the
transformer at P1 are reading a value of 10-15v.
I am working from memory, but IIRC there's a connector with 8
black wires that carries the transformer secodnary
connections (4 windings, 2 wires per winding). It goes into
the power distribution PCB, and each winding it then
connected to one of the regulator 'bricks'.
Now, you should see 20-30V _between the 2 wires going to a
particular regulator_. Not between either wire and earth.
If you measure the voltage between a particular wire and
earth (logic 0V rail, case, whatever), then you'll see one of
2 things.
1) If there's no regulator connected to that winding, you'll
measure 0V.
The winding is electrically isolated from the rest of the machine
2) If there is a regulator connected, then each wire will
swing between ground and the full secondary voltage at mains
frequency, due to the action of the bridge rectifier in the
'brick'. Now, what that will appear at on your meter depends
on the meter, but I could well believe some would average it
out to half-voltage.
So that's the first explanation, you're measuring the voltage
between one end of the secondary and ground, not the voltage
across the secondary.
A second explation, if you are measuring the voltage across
the secondary, and it's half what you expect, is that the
primary windings are wired incorrectly. The power
transgformer has 2 primary windings, rated at 115V each. For
115V mains, you connect them in parallel (taking care of the
phase, of course!), for 230V mains you connect them in series
(ditto). The primary windings go to a 4 pin connector that
plugs into the front of the AC input box. There are 2
different AC input boxes, for 115V or 230V mains which
connect the pins of that connector appropriately -- there are
other internal changes relating to the mains switching
contactor and its control supply. Is it possible that you
have a 230V unit plugged into a 115V mains socket?
I highly doubt this as the AC input box is clearly marked 120V.
So that leaves two possibilities. It's either the
transformer, or the
AC input box.
I thing it's very unlikely to be the transformer. Shorted
turns would make it get hot and bothered very quickly.
-tony