9 Mar
2007
9 Mar
'07
5:27 p.m.
Told ya'll I was going to dig back in to that 11/45 restoration project :)
Got the workroom cleaned up enough to actually have room to work on the
thing. Stripped it down to the very most basic configuration possible
(including getting rid of the 9312 for a 930, etc.). Barebones. No cards in
SPC slots except grants. Known good 16K of core and then a base processor
set (without segmentation and without FP).
Turned on the bottom 742, then the top one... fans all come on but nothing
on the front panel at all. Checked the obvious front panel keylock, it
wasn't off. Time to check voltages & ripple on the backplane.
E02B2 is at 0.55v, indicating the H745 in slot E is officially a problem
child.
E15A1 is at 0.95v and E01B1 is at 0.05v, so the +15v regulator built into
the top H742a is suspect. Noted that the small fan on the top of the top
H742a isn't turning so likely the regulator is well-done.
The test points on the backplane for regulators B, C & D are ok, as is
the -15v from the bottom H742a.
Time to get the H742a docs from bitsavers :)
Jay West
9 Mar
9 Mar
7:19 p.m.
I was looking at the power control board for the H742A (5409730) that is
supposed to be putting out my +15v. I couldn't find any schematics on this
board but the system engineering prints appear to indicate they should be
present. In the absence of schematics (and any obvious scorching) I figured
the likely first thing to check is the sole TO-3 power transistor on the
board. Sure enough, the C-E junction is shorted so at the least I'll need
one of those.
1) The critter is Motorola "DEC3000" which I'm betting is a DEC house part
number (since ECG xref shows nothing && it starts with DEC). Can anyone clue
me in to what part that really is?
2) Are the schematics for 5409730 around so I can try to understand it a
little better?
Thanks for any pointers!
Jay West
10 Mar
10 Mar
5:01 a.m.
On Fri, 9 Mar 2007, Jay West wrote:
I was looking at the power control board for the H742A
(5409730) that is
supposed to be putting out my +15v. I couldn't find any schematics on this
board but the system engineering prints appear to indicate they should be
present. In the absence of schematics (and any obvious scorching) I figured
I have the complete set that came with my 11/45. The schematics are on
the sheet titled "POWER CONTROL BD.", number 5409730-0-1.
And I had exactly the same fault in my H742 during operation. The fan was
stuck so the transistor and other parts got really hot...
1) The critter is Motorola "DEC3000" which
I'm betting is a DEC house part
number (since ECG xref shows nothing && it starts with DEC). Can anyone clue
me in to what part that really is?
Both the transistor and the schematics say Motorola MJ3000.
Please also check the zener D3, a 1N5353B (16V) that is connectec between
the base of the transistor and ground. I guess it is shorted.
2) Are the schematics for 5409730 around so I can try
to understand it a
little better?
Yes, I'll try to scan it (not easy because of the paper size).
Christian
5:04 p.m.
I was looking at the power control board for the H742A (5409730) that is
supposed to be putting out my +15v. I couldn't find any schematics on this
board but the system engineering prints appear to indicate they should be
They're in my PDP11/45 printset.
present. In the absence of schematics (and any obvious
scorching) I figured
the likely first thing to check is the sole TO-3 power transistor on the
board. Sure enough, the C-E junction is shorted so at the least I'll need
one of those.
Did you test it out-of-circuit? It's a power darlington (read : high
current gain) and there's a fairly low resistor (100 ohms -- 2 off 200
ohm in parallel) between C and B. It's quite possible an in-circuit test
will show it as shorted.
1) The critter is Motorola "DEC3000" which
I'm betting is a DEC house part
number (since ECG xref shows nothing && it starts with DEC). Can anyone clue
me in to what part that really is?
The pritn I have shows it (Q1) as an MJ1000
2) Are the schematics for 5409730 around so I can try to understand it a
little better?
I can describe the circuit for you..
Firstly a sort-of layout ;
With the PCB so that Q1 is at the bottom right, and the fat electrolytic
capacitor is on the far left, then :
That capacitor is C1. Alongside it, towareds the bottom of the board are
2 small transsistors. Q2 is near the bottom edge, Q3 jsut above it. Then
thers's Q1, the To3 can on the heatsink
Above Q3, roughtlu on a line with the top of that capacitor C1 is a
bridge rectifier, D1. And alongisde that is a fuse, F1
The rest of the compoonents on the board are part of the ACLO and DCLO
circuits.
Now, for a circuit description of the +15V supply.
30V AC comes in on pins 3 and 4 of J1 (the 4 pin connector on the board).
It's rectified by D1, and smoothed by C1. The +ve side of that capacitor
then gores to the fuse F1.
Nwo, the regualators is quite conventional. It consists of a 16V zener
with that 100 Ohm resistor arrangement I mentioned feeding it from the
outpt of C1. Q1 acts as an emttier-follower, and buffers the output of
the zener circuit to provide the +15V line to the rest of the machine.
Now for the unconventional part. Q3 and Q2 form a circuit that disables
the +15V supply (shorts out the zener, effectively) if the DCLO line --
the 'spaer one' on pin 9 of J4 (the conencotr wired to the PCB) -- is
aserted.
So, what I'd do is ; Check F1. If it's OK. power up and check the voltage
on the +ve side of C1 wrt the system ground rail. You should have 30-40V
here. If you do, check the base voltage of Q1. If that's 16V, and you
still ahve no output, suspect Q1. But if that's essentially 0V, check Q2
and Q3, and if they're OK, it's time to check back into the DCLO circuit.
-tony
9 Mar
9 Mar
7:19 p.m.
E02B2 is at 0.55v, indicating the H745 in slot E is officially a problem
child.
That's a -15V brick, isn;t it..
E15A1 is at 0.95v and E01B1 is at 0.05v, so the +15v
regulator built into
The -15V bricks need a +15V supply from the PCB in the front section of
the H742, as well as the 30V AC input from the transformer. So there
might only be one fault here.
the top H742a is suspect. Noted that the small fan on
the top of the top
H742a isn't turning so likely the regulator is well-done.
You do have mains going to that supply, right? (yes, I know it's obvious,
but it's worth checking).
The PCB in the front (+8V, +15V, LTC, etc) is acutally quite simple
(IIRC, linear, not swtiching, regulators, for example). If that's where
the fault is, you've got a fairly easy day ahead...
IIRC, there's at least one fuse on that PCB.
The test points on the backplane for regulators B, C
& D are ok, as is
OK, so you do haev mains, and the transformer is probably OK.
the -15v from the bottom H742a.
That '-15V' is odd if it's the rail I think it is. The '+15V' output
of
the 'front PCB' is tied to the system ground rail, so the '0V' line o
nthat PCB is actually at -15V wrt ground. That's why the prints tell you
not to use the LTC, ACLO, etc pins on the lower H742 (they'd be
references to the -15V rail, not system ground).
-tony
6339
days inactive
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4 comments
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ard＠p850ug1.demon.co.uk -
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