Friday, July 21, 2017

Crisis.....Averted... (but a lost night...)

On Tuesday 18th July, Jonathan headed out to the observatory to find beautifully clear skies perfect for some follow up imaging.  After getting set up and ready to grab some data, the remote connection to the dome PC from the bunkroom suddenly failed.  Checking upstairs the dome PC was no longer powered up - and - even worse, wouldn't actually power up.

Even the IT support favourite advice of "turn it off and turn it on again" (well unplug it completely) did not manage to solve the issue.  Unable to contact Steve initially, Jonathan headed out to make the most of the clear skies with some DSLR astrophotography.

The following night Jonathan and Steve managed to hurry along the Auckland Astronomical Society council meeting members with a view to getting out of the meeting and up to the observatory as quickly as possible - with a spare computer power supply in hand.

Almost as expected (remember Murphy?).. the PC powered up instantly...

The challenge was working out WHY the PC had failed because having unreliable equipment is certainly going to have a negative effect on our efforts.  Out came the power supply tester (Steve's a professional IT nerd so has these things lying around...) and everything looked good... fearing the worst... the "intermittent problem"... Steve reconnected everything and powered up again to start some additional diagnostics.

One common cause in the PC world when something goes off suddenly and won't power back up (even with a "power cycle") - but then does some time later (maybe many minutes later) - is that there has  been a short circuit, power surge or "overcurrent" problem somewhere on the motherboard or power supply.  Most IT techs have seen this most often when an errant screw accidentally makes its way (purely by itself you understand) onto the exposed boards of a PC.  The protection circuity (such as polyfuses) kick in and power is removed.  It is common not to instantly come back on when the fault is removed.

The hunt was on - for insects in the power supply, "errant screws", possibilities of electrical surge (though the surge protector was still functioning).  Nothing was obvious ... so case back on and stand the PC back up.

At that point the probably cause of the issue was suddenly staring us in the face... the bright blue power LED (which is normally covered loosely with black electrical tape) was off... whilst the PC was on.  Jonathan was certain the light was on the night before when he was setting up and checking inside again, it was still connected.

It seems likely that the blue LED had failed, which in turn had tripped protective circuitry on either the motherboard or the power supply.  The mystery solved, we could be a lot more confident it wasn't going to happen again, and we took the opportunity to do something that should have been done when Steve built the PC - disconnect the Hard Disk and  power lights completely to protect the darkness of the dome.

With that resolved, and the skies clearing, Jonathan and Steve set out to grab some images of a new high priority microlens target OB171186.  Joanathan managed to get 28 300 second images over the next couple of hours - though had a few problems - the strange and as yet undiagnosed mount disconnection (from an earlier blog post) and an issue plate solving a number of (most of) the images in PinPoint.

Light Curve from OB171186
Steve processed the images next day for upload and managed to get the astrometric solution by reducing the number of star used for the solve and also narrowing the intensity range used for matching in the PinPoint settings.  This seemed to do the trick.  Steve also ran the images through a tool called PySIS - which uses differential image analysis to generate a photometric light curve.

Posted by Steve Hennerley

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