[pvrusb2] Weird behavior with my Happauge UB-PVR

[Mike Isely]

On Thu, 20 Mar 2008, Eric A. Bonney wrote:
> 
> I actually only see the issue of the USB HDs changing where they are 
> mounted at boot time. After that they are always good and they are 
> plugged into the same power/surge strip as the PVR. I am guessing that 
> the PVR may be more sensitive than the HDs. If it is a dirty power 
> issue any suggestions on how to resolve the issue?
> 

Well not knowing anything about your USB hard drives, I can't really 
make any comparison about how sensitive they might be compared to the 
PVR.  The real sensitivity is probably going to depend on how good the 
power brick / wall wart is.

One thing people don't immediately realize (and I've said this many 
times in the past) is that PC power supplies are going to be much more 
robust than an external power supply for a USB device.  A PC power 
supply manages hundreds of watts and has considerable internal 
capacitance which can carry it across momentary power glitches.  I kid 
you not - I have personally witnessed having the lights blink out in my 
house for 1/4 - 1/2 second and the PC (no UPS!) sails right through it 
without a hiccup.  Compare that to a power supply for a USB device - 
such a device will typically be a tiny little switcher with a very low 
power rating and not much internal capacitance.  A wall wart is not 
going to be able to sustain its output voltage when there are "gaps" in 
the incoming power.  A wall wart also isn't going to have anywhere near 
the filtering of a PC power supply.

I've seen people get unwelcome surprises due to this.  They think the 
power in their house is clean - because the PC is fine, and then start 
scratching their heads when the PVR seems to randomly reboot / reconnect 
once or twice a day.  Because the PVR is "on its own" as far as power 
supply is concerned, it can't benefit from all the filtering / capacity 
of the PC power supply.  (And this is not a fault of the PVR since 
USB-supplied power is limited to 1/2 amp at 5 volts (2.5 watts) which is 
not enough to run the PVR.  This is why 3.5" external USB hard drives 
all have external power while far more power-efficient "laptop" style 
external USB hard drives frequently / barely can run directly off the 
USB cable.)

There was a case a while back of a pvrusb2 user seeing these symptoms.  
He ultimately traced the root cause as being the air conditioner in his 
house.  Every time it turned on, it glitched the AC power in the house, 
causing his PVR-USB2 device to reset.  His PC was never affected.

I would start by plugging your PVR into a surge protector.  If the 
problem is surges or EMI, the the surge protector's filtering should 
help.  If however the problem is due to actual fraction-of-a-second gaps 
in the line power, then a surge protector won't help.  In that case you 
need a UPS.  Heck, just get a nice UPS, plug your PC into that and then 
plug in your PVR to it while you're at it.  If the problem really is 
dirty power, then that will definitely solve it.

  -Mike


-- 

Mike Isely
isely @ pobox (dot) com
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