[mythtv-users] HDPVR intermittent failure

Greg gregl at nycap.rr.com
Sun Jun 28 16:31:45 UTC 2020

On 6/27/20 9:46 PM, DryHeat122 . wrote:
> On Mon, May 11, 2020 at 12:59 PM DryHeat122 . <dryheat122 at gmail.com 
> <mailto:dryheat122 at gmail.com>> wrote:
>     On Mon, May 11, 2020 at 2:41 AM Stephen Worthington
>     <stephen_agent at jsw.gen.nz <mailto:stephen_agent at jsw.gen.nz>> wrote:
>         On Sun, 10 May 2020 20:20:30 -0700, you wrote:
>         >On Sun, May 10, 2020, 7:58 PM Greg <gregl at nycap.rr.com
>         <mailto:gregl at nycap.rr.com>> wrote:
>         >Ok thanks I will investigate that.  But it's been working
>         fine with the
>         >current power source for like a year now, and others on this
>         list use it
>         >too.
>         USB cables often fit badly into the sockets.  If so, the
>         connection
>         generally gets worse over time as you get dirt or oxidisation
>         on the
>         contacts.  So badly fitting cables will degrade with time. 
>         The result
>         is that the voltage drop across the cable will increase
>         markedly.  And
>         they can be too thin - the amount of copper in the wires is
>         too little
>         and that causes high resistance and a big voltage drop across the
>         length of the cable.  Some (most?) USB cables are designed
>         only for
>         data transmission, or to run very low power devices. For a
>         high power
>         device, you need a better (thicker) cable.  The high power
>         devices do
>         a negotiation with device supplying the power and request high
>         power
>         mode.  If the cable is not capable of high power, that
>         negotiation is
>         not supposed to work and the device should either only work in low
>         power mode or it should turn itself off.  But USB cable makers
>         often
>         make cables not capable of high power transmission that will
>         allow the
>         high power mode negotiation to succeed.  So even though the device
>         supplying the power is sending high current, the voltage drop
>         in the
>         cable means that at the other end, the voltage can be below
>         the level
>         required for proper operation or to fully charge the device's
>         battery.
>         I have had two notably bad experiences with USB cables.  One
>         was a USB
>         DVB-T tuner, and it was very like your experience - it would
>         go for a
>         number of days just fine, then suddenly stop.  If I unplugged
>         it and
>         plugged it in again, it would usually work again. When I finally
>         investigated properly, I found the cable was just a little
>         loose in
>         the PC's socket.  I replaced the cable with one that fit more
>         tightly
>         and the tuner was much more reliable.  It still occasionally
>         caused
>         trouble, but only when I had bumped the cables (or in one
>         case, after
>         we had a small earthquake).  So because of that and because I
>         needed
>         more DVB-T tuners, I finally replaced all my DVB-T tuners with
>         an 8
>         tuner PCIe card.
>         The second bad experience was my Samsung Galaxy Tab S2
>         tablet.  Its
>         USB charging cable was supplied with it by Samsung, so I
>         assumed it
>         was a good one.  But right from the start, the tablet took a
>         long time
>         to charge, and the time gradually got longer and longer and the
>         battery life on one charge was getting less and less. And then I
>         started to have to jiggle the cable in the socket to get it to
>         charge
>         at all.  I actually called the Samsung help line about this,
>         and they
>         said it sounds like a bad cable.  So I bought a expensive (NZ$30)
>         Pudney & Lee charging cable, which was a fair bit longer than
>         the old
>         Samsung cable, but fit very tightly at both ends and was
>         significantly
>         thicker - it has more copper in the wires in the cable.  Then
>         suddenly
>         the battery charging times were what was specified for the tablet,
>         rather than three times as long.  And over a number of charging
>         cycles, the battery life came back again.  So the original Samsung
>         supplied cable was clearly bad from the start - it is probably
>         less
>         than the specification required to charge the tablet properly
>         as it is
>         too thin and has too much voltage drop even when the plugs fit
>         properly.  So definitely NZ$30 well spent.  But I am surprised
>         that a
>         reputable company like Samsung would supply a bad cable with an
>         expensive top-of-the-line product like my tablet.  But they
>         did - so
>         now I always suspect any USB cable I get and keep an eye on
>         how well
>         it is working.
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>     Thanks for all the suggestions.  I will investigate all of them. 
>     Something I do not see in here is an opinion that some software
>     problem could have evolved.  I was kind of thinking of that as a
>     possibility given that it worked fine for so long then seems to be
>     degrading.  OTOH I never thought of the possibility that the USB
>     connection could be degrading.  I'm going to try Greg's connector,
>     assuming I can get parts during the Apocalypse.  Also, his link
>     specifies Radio Shack parts.  What's Radio Shack?!? ;-)
> Well folks this is getting frustrating.  I addressed a possible 
> ventilation issue.  I also unplugged the power cord I had from the 
> Myth box USB and connected it to an old iPad charger rated at 5V/2A.  
> No help.  It wouldn't record anything, no matter how much rebooting 
> and power-cycling. So I concluded the HDPVR was hosed and got a new 
> one (more accurately, a replacement circuit board for it).  Powered it 
> with the same wall wart.  Recorded great for a day.  Just turned it on 
> and I have failed recordings and it won't respond when I try to 
> manually play a channel.  Reboot, and it works fine, same pattern as 
> before.
> I finally got a molex connector and am still going to try what Greg 
> suggested, but I really don't think it's a power issue.  Apply makes 
> good electronics and that wart has the same specs as the power supply 
> that comes with the HDPVR. The HDPCR isn't overheating.  It's not the 
> HDPVR itself. That only leaves the software on the myth box.  Anyone 
> have ideas how to troubleshoot that?
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  The next time it won't record,try to cat it and see if it responds.  
This is the command I use,  cat /dev/video0 > test .. dmesg for the 
proper port it's connected to. This may help too see if it is the 
software or not..

I am curious were you got the motherboard? There used to be a place in 
Ohio (I believe) ,but they have gone out of business.

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