Ebay amp. Is it DOA?

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Finished Board New TPA3123 2 1 Digital Power Amplifier Board Subwoofer Output | eBay

Came last week. Finally got around to bench testing it. Used a 15vdc 3amp Toshiba SMPS. 3.5inch Vifa 8ohms mains and 4inch Dayton Neo woofer.
Signal from preamp. Checked, double checked, polarities.

Turned on the music, plugged in the power supply, and nothing. Just a steady approx 3 beat per second low volume "blip" coming out of the main speakers. Nothing out of the woofer. Volume, treble, and bass level controls have no affect whatsoever.

I swapped the power supply for a 19vdc 4amp Sony SMPS and the result was unchanged. I used a DMM both times to be certain the center pin power input was seeing positive.

I disconnected the signal input. No change. Same 3bps blips.


I'm well within my 15day return period and the guy's got a big store with 98.9 approval so I'm not too worried.
Some Lepai buyers stated that their amp didn't kick on for several moments after turning it on. I couldn't say whether that was due to the amp circuit or the SMPS or a flaky connection somewhere. I'd make some on-board voltage checks before (literally) wrapping it up.
Sometimes these things don't turn on when they are under-voltage. Certainly that's true of some of the Tripath lot.

I don't think this is a brain-dead idea, but someone please catch it if it is, but get a PP3 and put it in series with your supply to get it a bit closer to the 30V limit.

One other thing occurs to me and that is the orientation of that power supply socket/plug. Those cylindrical things are horrible and seem not to be subject to any universal standard and no one ever knows which is positive (hence numerous Sony Walkman Pros being blown because of them - and what a rat's nest to repair!). It could be your supply doesn't match the way they have it oriented. Hopefully there will be a diode in there, if only at the outputs, and you won't have blown anything, but this would certainly be worth checking.
Je@#s F#ckin& Ch*i$t I am an idiot!

The vendor suggested something similar regarding the plug and advised me to take a measurement at the pins underneath with my meter after the supply is plugged in. I did so and something just seemed intuitively amiss at that point.

By a sudden demoralizing insight I scanned down to my DMM and the red/black leads were reversed. WTF. All this damn time deciding on an amp, waiting on China mail, and effort setting it up. With a little chip amp like this, 19.5 volts at 4 amps probably fried it good and permanent. I don't know whether to cry or pound a nail with my forehead.

Once I got the polarity corrected the amp works. But the "sub" channel is gone, and there remains a vestige of that 3bps in the background.

I'm so enamored with the size and function of this amp I guess I'll just order another one. 23 dollars free ship. That's not too hard a hit for being a numbskull.

*whenever I do something this boneheaded I have to remind myself of the 1998/99 Mars orbiter debacle...

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