23 Mar
2016
23 Mar
'16
9:21 p.m.
On 3/22/16 12:29 AM, Mattis Lind wrote:
So I had a few minutes tonight to investigate a few things:
- The startup PSU is running, and the relay in the 5V supply is firing
and stays energized until the supply is powered off.
- The +5V, and +/-12V bias voltages are being properly generated. This
makes sense, since the 2.5V supply is working fine. From my
understanding of the supply, this means the 300VDC is also present (also
validated by the relay firing.)
- The 20Khz clock generated on the bias board is present (measured from
pin 8 of J1 on on the bias board), at the proper rate and duty cycle.
- 5V AC and DC LO signals (measured at J1) are .3 and .9V, respectively.
So far, so good. I also measured the 5V Overcurrent and 5V Crowbar on
J1 (pins 2 and 19) and they're at 12V and 8V respectively. I'm not sure
I understand what this indicates; the Overcurrent lamp is not
illuminated on the power controller, for example, and per the tech
manual (section 4.4.2) if an overvoltage occurs and the crowbar kicks
in, the supply should shut down for ~1 second, which I'm not seeing any
indications of (I'm not seeing the voltage reach anything over .2V with
a small load attached). The overcurrent protection appears to work
similarly. I don't see an indication of what the levels for the signals
on J1 are supposed to be, however.
I'll hopefully have more time to debug later this week, thought I'd
report my findings and see if anyone has any bright ideas.
Thanks as always,
- Josh
such good
luck. No smoke or fire, but now I get nothing at all out of the
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.
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