[mythtv-users] HD-PVR power supply (wall wart) gone bad

Bert Haskins bhaskins at chartermi.net
Sat Dec 1 15:52:25 UTC 2018

On 11/30/2018 8:55 PM, Bob wrote:
> On 11/8/18 2:14 PM, Will Dormann wrote:
>> On 11/8/18 10:39 AM, Dan Wilga wrote:
>>> I, and others, have
>>> successfully replaced these wall warts with a cable that connects
>>> directly to the PC's 5v power supply. I essentially took the Molex
>>> connector from a dead case fan, moved the "+" pin from the 12v position
>>> to 5v, chopped off the bad wall wart's cable, and wired it to the pins
>>> on the Molex connector. Remember: Polarity is crucial!
>> +1 on this strategy.  I've been running my HD-PVR off of my MythTV box's
>> DVR for a few years with zero trouble.   I just run the wire out of the
>> back of the MythTV box (via an expansion slot cover that has a hole in
>> it) and to the HD-PVR.
>> Aside from being more reliable, one fewer wall wart is a neater setup!
> So, I made my attempt at a cable to replace my wall wart and my 
> recordings are not working so good. After re-reading this, it appears 
> I should *not* have used the 5V line even though the wall warts I have 
> show 5V @ 2A, right?
> Interestingly, the HD-PVR does power-on and is assigned a device 
> (/dev/video5 in this case). However, I attempted a 4 minute recording 
> and actually recorded for about 1 second. The "blue" light turned off 
> every 4 seconds, then back-on again.
> So, use the +12V line and not the +5V line?
Not unless you want to fry it!

Did you use a very long, very thin, or a long, thin cable?

Copper is expensive, so the wall wart is often set for a higher voltage 
to make up for the voltage drop in the wires.
So what you are reading is 5V at 2 Amps at the plug when loaded with the 
full two amps.
The voltage right at the WW could be higher.

Now when you pick off the +5 at the pc you may be dropping enough 
voltage along the wires to result in unstable operation.
You are definitely creating a ground loop this way and that can cause 
it's own set of problems.

I have yet to repair a HDHR WW or even a recent TV that had capacitors 
rated for over 30000 hours of operation.
At ten hours a day that is less than one year YMMV.

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