22 Mar
2016
22 Mar
'16
10:53 a.m.
On Tue, Mar 22, 2016 at 12:29 AM, Mattis Lind <mattislind at gmail.com> wrote:
the
Yeah, I have actual original copies of the printsets, too. I have no
excuse, I just get nervous working on these things. I suppose eventually
I'll get used to it.
>> Good
news - mine worked so fingers crossed for yours too. I now have a
> functioning PSU again though I've not tried it back in the chassis
yet...
Nice! My replacements arrived today and unfortunately I did not have
such good
luck. No smoke or fire, but now I get nothing at all out of supply. The whine is gone, but there's
nothing output at all. The
fuse/resistor didn't blow (it's still got continuity across it) and the
transistor I replaced is still fine, but there must be something else in
the supply that's causing issues...
Blargh. I hate working on power supplies.
In this case you have an excellent technical manual and a good schematic
which should help a lot. Working with big SMPSU without schematics or
technical manuals is a not fun.
So here is my piece of advice directly from my head.
1. The PSU has really two AC inputs wired together in the input harness.
You can separate the startup supply part from the SMPSU part. Connect the
startup PSU to a separate AC input and the SMPSU part to a insulation
transformer, a variac and lightbulb in series.
2. Check that the startup PSU, that uses a normal 50/60 Hz transformer
gives the correct voltage. +11 if I remember
correctly.
3. There is a circuit that monitors the input rectified 300VDC voltage and
enables the relay when it has reached a proper voltage. It is a soft start.
Disable it for temporarily. Good idea to check that is working though. If
not the soft start resistors will become overheated when trying to run it
at full load.
The relay (and the circuit driving it) appears to be working -- I hear it
click on at power-up (faintly, over the roar of the fans) and click again
after power-down. I'll hopefully have some time this week to play around
some more, thanks for the suggestions!
I'll note that my earlier statement that I was getting "nothing" out of the
supply turns out to be slightly inaccurate -- with a load, I get nothing
(well, 0.07v) out of the 5V supply; without a load the voltage slowly
increases (maybe 0.5V per second). Didn't let it run long enough to see
where it ends up ;).
Thanks again,
Josh
4. Now you need to have the SMPSU section connected to
AC inlet. On one of
the daughter boards there is a switching bias supply. Check that it
generates the +/-12 V and +5V.
5. Is the main SMPSU switching logic making a nice square wave signal
output. The control board is yet another daughter board.
6. I disconnected the output terminals from the H-bridge to the transformer
and connected a dummy load to be able to have a look at the output
waveform.
7. Reconnect the transformer. The main switch produces +5V and +38V. The
38V is then used on the daughterboards to create all the other voltages,
+/- 12V, +/- 15V, +12V SB, +5VSB (depending on which supply). Is there 38V
here?
8. There is a crowbar circuit on the +5V output terminals. Check that it is
not tripping.
Please note that when working with the +2.5V supply it gets the bias
voltages from the +5V supply. So either get that one working first or
supply bias voltage from a regular PC supply.
/Mattis
- Josh