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Old 27th August 2012, 07:35 PM   #11
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alright, performed the recommended voltage and resistor checks. and it looks alright so far. nothing that is off.

i checked that none of the leads on the bottom side of the board is shorted to the case.

regarding the power switch i thought that might be it, but when i tried to do the current test(with the switch on and properly working), it will "malfunction" again.

this video will shows the issue. Initially its working normally, but the current test is a "100% sure" way to trigger the problem(you can hear the buzz and there is 8volt DC on output). So to fixed it, i have to hold the power button halfway then switch it on fully. i am thinking it is something to do with capacitor. (since holding it halfway discharge it?)

<embed width="440" height="420" type="application/x-shockwave-flash" src="http://v6.tinypic.com/player.swf?file=sfym3n&s=6"><br><font size="1"><a href="http://tinypic.com/player.php?v=sfym3n&s=6">Original Video</a> - More videos at <a href="http://tinypic.com">TinyPic</a></font>

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Old 27th August 2012, 10:48 PM   #12
agdr is offline agdr  United States
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Quote:
Originally Posted by ritsute View Post
When i measure my P2 pad, i find that there is 8volts DC output. Measuring my U3,U4 pin 1 and 7 yield the same voltage. Normally when it is function normally, it shows 0Volt (analog signal).
See if the second half of this post sounds like what you are experiencing:

The Objective2 (O2) Headphone Amp DIY Project

and this

The Objective2 (O2) Headphone Amp DIY Project

When your O2 is messing up, see if the output voltage is actually climbing up to the 8Vdc from 0Vdc over the course of a second or two as in that second posting (start the amp up with the DMM attached to the output).

If so, the solution might be here, reheating the connections on R12 and R13 even if those solder connections look perfectly OK.

The Objective2 (O2) Headphone Amp DIY Project

The Objective2 (O2) Headphone Amp DIY Project

If those don't make contact then the input bias current of U3 and U4 charges up C13 and C14 to nearly the power supply rail voltage, which in turn puts a large DC voltage on the O2 output due to the unity gain buffer stage. If it is a bad solder connection like that then it would be typical for the problem to come and go.

Last edited by agdr; 27th August 2012 at 10:59 PM.
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Old 27th August 2012, 11:19 PM   #13
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opps look like the forum didn't embed the link. Video - TinyPic - Free Image Hosting, Photo Sharing & Video Hosting

mmm and its not quite the same issue. I managed to listen to run it till the battery died. Sounds normal to me. my R12 and R13 measured 40k. which sounds just about right? But i'll try reheating it later.

And the current test is not a "100% sure" way to trigger the problem now ><. cant get it to malfunction. You can see the video i posted. if its not malfunctioning, its working properly.
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Old 27th August 2012, 11:33 PM   #14
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Quote:
Originally Posted by ritsute View Post
mmm and its not quite the same issue. I managed to listen to run it till the battery died. Sounds normal to me. my R12 and R13 measured 40k. which sounds just about right? But i'll try reheating it later.
During a time when you are getting 8Vdc on one of the O2 outputs, try measuring the voltages on U3 or U4 (whichever one corresponds to the faulty output) and see what you get on all 8 pins. Measure the voltages between the pins and ground, which is the metal shell of the gain switch.

NOTE: 8Vdc on the O2 output is enough to damage headphones! You may want to leave your headphones unplugged until that one gets fixed.
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Old 27th August 2012, 11:46 PM   #15
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Alright i got it to malfunction. Pin 1 to 8 respectively is 7.94, 7.92, 1.23, 1.73, 1.22, 7.90, 7.90, 8.48 volts. DC output is immediate. On both channel.
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Old 28th August 2012, 01:40 AM   #16
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Quote:
Originally Posted by ritsute View Post
Alright i got it to malfunction. Pin 1 to 8 respectively is 7.94, 7.92, 1.23, 1.73, 1.22, 7.90, 7.90, 8.48 volts. DC output is immediate. On both channel.
OK, pin 4 at 1.73Vdc to ground is probably the bad guy. That is your negative power supply rail, and should be around the negative value of whatever is on pin 8 to ground, so somewhere around -8.48Vdc. Without having their proper negative supply rail voltages, U3 and U4 are just doing the best they can with the rest of those voltages. If you can, when the O2 is messing up, also measure the voltages on U2 pins 4 and 8, both with respect to ground (gain switch shell).

So... I would guess bad negative mosfet (Q2) and/or a bad U2, assuming that U2 pins 4 and 8 measure with proper power supply rail voltages. There have been posts in the big O2 thread where people with loud turn on or turn off transients solved them by replacing either or both of those (Q2 and U2). In the comments on RocketScientist's site for the O2 he states at one point that bad mosfet(s) can turn on or off too slowly, creating the pops.

If you decide to try replacing them, and have to order parts, probably good to order both Q1 and Q2 along with a U2 to have on hand for troubleshooting.

Last edited by agdr; 28th August 2012 at 01:48 AM.
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Old 28th August 2012, 02:10 AM   #17
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Somehow when i try measuring U2, the amp will go back to normal. This is weird.
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Old 28th August 2012, 03:00 AM   #18
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Quote:
Originally Posted by ritsute View Post
Somehow when i try measuring U2, the amp will go back to normal. This is weird.
That can also be the sign of a bad U2 or mosfet - or bad solder joint. Sounds like your meter hooked to the circuit is causing the negative rail part of the power management circuit to toggle from off to on.

It couldn't hurt to try re-heating all the solder joints in the power management circuit. U2, both mosfets, R8, C21, R6, R25, the LED, and all the other resistors and capacitors in that area. Just another 1 second or so with the soldering iron on each.

Last edited by agdr; 28th August 2012 at 03:04 AM.
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Old 29th August 2012, 03:13 AM   #19
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I don't quite understand how the meter being hooked up to the circuit is causing the negative rail part of the power management circuit to toggle from off to on. Ordered another pair of MOSFETS to swap it out.
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Old 29th August 2012, 05:10 PM   #20
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Quote:
Originally Posted by ritsute View Post
I don't quite understand how the meter being hooked up to the circuit is causing the negative rail part of the power management circuit to toggle from off to on. Ordered another pair of MOSFETS to swap it out.
Noise injection from the test leads, if just the right conditions occur. If Q2 doesn't solve it, do try U2 also. A couple of cases of bad U2s have caused similar things. Good luck!

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