[pvrusb2] Fun with heat / power [was: (an indescipherable string)]

[Jan Brouwer]

Thanks for all the help!
I will start some experiments and post the results.

Sorry for the "indescipherable string" I screwed up trying to reply with a
"mailto:" using the gmail-webinterface...

Cheers,
Jan

2013/7/14 Mike Isely <isely at isely.net>

>
> (see below)
>
> On Fri, 12 Jul 2013, Gary Buhrmaster wrote:
>
> > On Fri, Jul 12, 2013 at 8:24 PM, Jan Brouwer <jan at brewsky.nl> wrote:
> > ...
> > > My unit does get pretty hot... I didn't think of cooling it before, so
> > > maybe that would do the trick!
> >
> > Certain Hauppauge devices have a history of getting hot
> > and resetting.  Certain Hauppauge devices also have a
> > history of having power supplies going (partially) bad
> > (especially if they are a few years old).  Either can cause
> > "random crashes".  Since it is (usually) the easiest to
> > test (unless your computer is next to the refrigerator :-),
> > I always swap out the power supply first.
> >
>
> Yes, this is definitely the case.  In fact, back in prehistory when I
> was much more a hardware hacker than a software guy I learned that when
> digital circuits misbehave the FIRST thing one should always suspect is
> the power supply!
>
> To summarize various previous discussions on this topic, the things I've
> seen over the years:
>
> These units do dissipate heat.  If you have it sitting in the open
> ambient air (with the room at a normal comfortable temperature) then it
> generally should not be a problem.  But if the device is in a closed-up
> box where there's no air circulation or if perhaps it's stacked with
> other heat-generating devices, then you may have problems with crashes /
> resets.  I do remember one specific tale a number of years back where
> the user had stacked 3-4 24xxx devices on top of each other and then
> stuffed them in a closed box.  That didn't work out so well :-)
>
> I find that people get frequently fooled by bad power.  The issue here
> is that normal PC power supplies are in fact very forgiving of bad mains
> - typical PC PSUs have large capacitors and a lot of internal
> protection.  They're designed to process/condition 300-700 watts without
> wasting a lot of energy and it takes a good design to do that.  I've had
> PCs actually keep going perfectly even when the building power fails for
> a fraction of a second.  The monitor might wink out for a moment but the
> PC just keeps truckin' along.
>
> USB-powered devices (well, those not connected to a powered hub...) have
> the benefit of drawing power from that nice stable PSU.  But any
> peripheral which is self-powered with, say, it's own little power brick
> is at a disadvantage.  Power spikes, brown-outs, or just plain saggy
> power won't affect the PC but the cheap wall-wart just can't defend
> against crap like that.  It doesn't have the same quality of filtering,
> and it is just too small to have enough hold-up capacitance to survive a
> dropout.  That leads to situations where strangely enough pvrusb2
> devices seem to randomly crash while the PC itself is unscathed.
> People frequently conclude that the device is flakey when in fact it's
> just bad power that can't be compensated by a simplistic power brick.
>
> So people seeing pvrusb2 resets don't immediately suspect bad power
> because, well, the PC is not crashing...
>
> Even a surge protector won't help the situation if the problem is
> dropouts or sags - surge protectors just block damaging spikes and
> filter EMI but they don't store energy to cover glitchy power losses,
> even for a fraction of a second.  For that you need a UPS, and one that
> is fast enough on switchover to keep from glitching the power brick (I
> think most modern UPSes meet that requirement).
>
> One big tip-off of bad power is if you can correlate pvrusb2 crashes
> with external electrical events, like say your refrigerator cycling or a
> nearby A/C compressor turning on/off.  A sump pump could even glitch
> things.  Anything that can suddenly draw (or cease drawing) large loads
> can do this.  And inductive loads - like a motor - can really screw with
> your power.
>
> And yes, I've seen reports of people who have correlated pvrusb2 crashes
> with their A/C compressor cycling on/off.  (Though it has been a few
> years...)
>
> You won't be able to analyze bad power with a voltmeter (analog, DMM,
> DVM, whatever..).  The events you are looking for will be too fast and
> the meter is usually filtered internally for slower (more readable)
> response.  If you really want to look for glitches, use an oscilloscope
> - but BE CAREFUL - you're messing with high voltage + high current which
> can seriously injure or kill you.  You can blow up the scope if you get
> the grounding wrong!  Actually it would be safer instead to 'scope it
> indirectly - say look at the output of a doorbell transformer wired to
> the mains.  Then at least it's isolated, current-limited 24VAC instead
> of 120VAC or 240VAC (depending obviously on your country's power grid).
>
> Anyway, if you suspect bad power, one easy test for this is just to plug
> the pvrusb2 device's power brick into a UPS.  If you suspect heat
> issues, try just using a simple desk fan to blow air across the top for
> a while.  If either experiment changes the behavior then you know you're
> onto something.
>
>   -Mike
>
>
> --
>
> Mike Isely
> isely @ isely (dot) net
> PGP: 03 54 43 4D 75 E5 CC 92 71 16 01 E2 B5 F5 C1 E8
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-- 
Jan