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O2 amp stopped working. Any known weak areas to troubleshoot first?

post #1 of 11
Thread Starter 

Huh. My Objective2 amp just stopped putting out sound. One minute it was working fine, and half-way through a Pandora song (via iPhone and LOD) the audio just stopped.

 

At the time of failure, there wasn't a pop or anything noticeable. The ON light still shines. I've unplugged it from power and swapped LOD cables. Swapped from iPhone input to my typical external DAC input. Nothing. No sound.

 

Whereas there used to be a small "thump" upon powering on or off, there is nothing now. No amount of plugging or unplugging -- or on/off or gain toggle -- results in any audible noise through my sensitive Etymotic hf3.

 

I can't open it up because I don't have the volume pot hex wrench at the office. I'll open and look around tonight.

 

Are there any known trouble spots or components likely to crap out on the standard BOM?

 

Is my only recourse (short of SEEING something messed up) to buy a multimeter and do something with it? Yes, I'm a decent builder, but a complete noob at diagnostic.

 

I built the unit myself, following the components list and instructions on NWG's site. I'm 85% confident that I had good joints and a solid overall build. The 15% of uncertainty is due to having to desolder and flip Q1 and Q2.

 

Any help is appreciated!

post #2 of 11

Well, it could be related to the power management circuit that includes Q1/Q2. It can cut off the power to the audio op amps entirely while the LED still remains on. Of course, make sure that there are no actual power problems.

post #3 of 11
Thread Starter 

Thanks for the suggestion, stv014. I've ordered new Q1 and Q2 units, along with new headphone jacks.

 

I also found NWG's diagnostic instructions and measurements. And I'll borrow a friend's multimeter later this week.

 

Hopefully the Q1 and Q2 swaps will solve the problem. Regardless, I'll probably teach myself how to use the multimeter.

 

Any other suggestions are appreciated!

post #4 of 11

Yeah, if both channels have gone down but the LED lights with normal brightness, then the area in which the fault lies is very likely limited to the power control. It's most likely a fault in the active devices and Q1 and Q2 are suspects, but so is U2, the NJM2903, which could be dead or misbehaving. Check that U2 has no dry joints on the IC pins which might upset the drive to Q1 and Q2. If U2 is socketed you can check it's OK by replacing it more easily than unsoldering Q1 and Q2.

 

post #5 of 11
Thread Starter 

Thank you for the additional info, wakibaki! I'll pay special attention to U2 as well as Q1 and Q2.

 

Hope to get the parts and multimeter in a few days.

post #6 of 11
Thread Starter 

Well I have a strong (and surprising) candidate for failure ... the wall adapter!

 

Borrowed my friend's multimeter and was going through NWG's troubleshooting suggestions at work. Since the amp is at home, all I could do was test the wall adapter. It comes up 0.0 on output voltage!

 

Ran the same test with my Pico wall adapter and it came up 12V as expected. Funny thing that I just noticed... the O2 and Pico share the same wall adapter (same voltage, same plug form factor). So I plugged in the O2 adapter into the Pico and no charging light came on. EUREKA!

 

So likely the adapter crapped out awhile back and the batteries had been draining the last few days. And Monday is when they lost enough power to shut down audio output, but still had enough juice to light the LED (which I know from experience is normal behavior).

 

I will head home after work with Pico adapter in hand. If all goes well, I will have regained confidence in my O2 build and will have only spent $10 on MOSFET and jacks that I may use in a future build.

post #7 of 11
Thread Starter 

Yup. A bum AC adapter is what I've got. Worked fine when I plugged in the Pico adapter.

 

New adapter (stepping up the 16V, 400mA version that NWG says is the best choice) ordered from Mouser.

 

Thanks for the suggestions provided. I'm glad the issue was much simpler to solve!

post #8 of 11

Thank you for this thread. O2 stopped producing audio, light on, all other parts of audio setup tested. Was getting really worried, read this thread and facepalmed; adapter not plugged in... :P

post #9 of 11

Thanks for the chuckle at your expense.  It really is the first step in troubleshooting electronics that won't turn on biggrin.gif  Make sure it's plugged in!

post #10 of 11
Quote:
Originally Posted by shadow419 View Post

Thanks for the chuckle at your expense.  It really is the first step in troubleshooting electronics that won't turn on biggrin.gif  Make sure it's plugged in!

 

Believe it or not, I have a BSc in Systems Engineering...

 

:D

post #11 of 11

I had given up on it until I read this thread.  I had the same problem, led power light came on but nothing worked.  low and behold someone had unplugged it from the wall.

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