[mythtv-users] HDPVR intermittent failure

DryHeat122 . dryheat122 at gmail.com
Sun Jun 28 01:46:09 UTC 2020

On Mon, May 11, 2020 at 12:59 PM DryHeat122 . <dryheat122 at gmail.com> wrote:

> On Mon, May 11, 2020 at 2:41 AM Stephen Worthington <
> 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> 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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