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Old 25th August 2012, 07:46 AM   #1
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Default My Objective 2 having weird issues

I built an O2 Amp and it works fine sometime and sometime it will screw up. I bought a DC adapter by mistake, so now i am waiting for my AC adapter to arrive. Testing using batteries now.

Normally when i turn my amp on, there is a loud transient sound. i have no idea if it is considered loud.

So my main issue is my amp works but there are time where it malfunction.
Sometimes when i turn it on, there is a louder than usual transient sound and there will be a constant hum. 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).

I found that if i switch the amp on realllly slow, it might fix the malfunction. So at the halfway mark, the LED will power on but dimly then turn on fully with a transient sound. Thou its a hit and miss situation so it might not work.

Another thing is, i was testing it using a small speaker, so when the amp was malfunction, i pulled the 3.5mm jack out and measured the voltage across one of my battery and immediately, my speaker started humming softly. Is there emi generated? this only happen when it is malfunctioning.


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Old 25th August 2012, 05:04 PM   #2
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Did you follow NwAvGuy's troubleshooting steps thoroughly?
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Old 25th August 2012, 05:08 PM   #3
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Yea only till resistance. Voltage wise I'm using batteries.
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Old 26th August 2012, 02:10 AM   #4
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Have you try another pair of battery?
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Old 26th August 2012, 04:07 AM   #5
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mmm i only have a pair of 9volt rechargeable. You reckon the problem lies on the battery?
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Old 26th August 2012, 04:34 AM   #6
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Without actually look at and try it, I suspect only. When trouble shot, start with the easiest one first.
If you don't want to buy a new battery, can wait for the AC adaptor to arrive. Plug it in and listen.
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Old 26th August 2012, 06:51 AM   #7
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Pull the socketed silicon, insert fully-charged batteries, and perform the recommended voltage checks.
Your last pic shows unnecessarily long leads on the bottom side of the board. Make sure they don't short to the case.
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Old 26th August 2012, 03:44 PM   #8
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socketed silicon? and the voltage check value is different on battery right?
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Old 26th August 2012, 09:59 PM   #9
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AKA the 3 0r 4 dip ICs (the 2903 is needed for the complete ps)
Different... most likely. A maximum of 9V x2 versus 11.7V x2. But the proportions should be similar. If a test point should be ~0V and it reads 4.5V, you know something is wrong no matter what the actual supply voltage.
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Old 27th August 2012, 08:05 AM   #10
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Sometimes the power on/off switch itself might be faulty causing improper +/-9V supply to the opamps resulting 8V DC appearing on o/p. As for humming sound - it might be improper grounding, try some battery operated source like ipod as AC operated source might be creating humming/noise. last but not least chk. for dry solder or best reheat all solder points again.
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