weird start up issue

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JR.
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weird start up issue

Post by JR. » Sun Sep 11, 2016 11:28 am

Got a good topic for this forum.

I mentioned some distress talking about my new surround system when I was unable to get sound out and had no way to check the light pipe audio feed.

After some trial and error I got it to make sound by unplugging are replugging the 5V power cord at the processor.

It turns out, if I use the outlet strip to apply AC power to the wall wart PS (probably SMPS), the surround processor lock up... All input LEDs on. OTOH if I apply the 5V after the external PS is stabilized by plugging into the 5V jack it boots up and works.

Many microprocessors connect their reset line to the +v and have enough delay built in that the PS stabilizes before anything bad happens. I suspect this external 5V supply has an unacceptable turn on profile, or is faulty.

I guess if I didn't understand how stuff works, I would just return it for another one that doesn't work (unless it's a rogue PS).

JR

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mediatechnology
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Re: weird start up issue

Post by mediatechnology » Tue Sep 13, 2016 7:28 am

Do you suppose the internal /RST capacitor needs to be bigger?
"We have grown to love our captors and demonize those that try to lead us to freedom."

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JR.
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Re: weird start up issue

Post by JR. » Tue Sep 13, 2016 9:10 am

I don't recall any reset cap for processors I work with (Microchip), just a pull-up resistor to +V There is digital delay built into the processor firmware routines. If the power supply is squirrely during this start up time I can imagine code corruption and lock up.

Just guessing, but perhaps a larger cap on the +5V rail might help smooth out any start up weirdness from the wall wart PS. If the PS maker to save cost ASSumes the load has capacitance on the 5V line, and the processor maker ASSumes the PS starts up cleanly and/or has an output cap.

I found an email address for the company, but my first answer from them in broken english is suggesting "shortage of voltage" :lol:

For now I will just leave it plugged into an un-switched outlet.

JR

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JR.
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Re: weird start up issue

Post by JR. » Wed Oct 12, 2016 3:47 pm

I finally got around to this again.

A new problem with leaving it running 24x7 is it will occasionally lose sync (guess). Low and distorted audio output, not up in all channels. I can reset it by hitting the mode switch or the input selector. While it may just be the processor getting stupid since it finds audio sync OK if TV receiver is turned off then on again...

Today the replacement external power supply ($6.50) from digikey arrived. I had to wait until I had enough parts to justify an order. I always remember something i needed "after" placing the order.

With the new PS plugged up and in the same switched outlet strip as my amps, it boots up perfectly. 8-) So the cheap Chinese PS that came with the unit was too cheap to work. :lol: The regulated voltage was spot on but i never put it on a scope to look at the waveform.

We'll see if I get curious enough to look at the PS further.

JR

PS: The suround sound is sounding pretty damn good... waiting for a coax driver I ordered to make a new center channel.

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