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Old 7th February 2013, 11:48 PM   #1
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Exclamation Objective2 - one channel doesn't work

Hello.
I am having a problem which I am unable to resolve myself because of my lack of electronic knowledge.

I've build an objective2 amp and the left channel is not working. I can only hear loud "boom" noise when switching the amp on or off. Right channel is working OK.
I am measuring about 13v of DC on this channel's output (measured from P2).

I've already build 2 O2s in the past and I've never experienced similar problem.

Does anyone know what the problem might be? I don't know much about electronic stuff so I have no idea what to do.

Sorry for my english
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Old 8th February 2013, 03:30 AM   #2
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Quote:
Originally Posted by ProTofik View Post
Hello....
I am having a problem which I am unable to resolve myself because of my lack of electronic knowledge.
Sorry for my english
List your O2 rel. querries on this thread-

The Objective2 (O2) Headphone Amp DIY Project

Chk the input socket, it might be faulty or dry soldered.
Use one end of i/p pin & chk for continuity of the i/p socket(blue)
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Old 8th February 2013, 03:32 AM   #3
agdr is offline agdr  United States
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Quote:
Originally Posted by ProTofik View Post
I've build an objective2 amp and the left channel is not working. I can only hear loud "boom" noise when switching the amp on or off. Right channel is working OK.
I am measuring about 13v of DC on this channel's output (measured from P2).
Try reheating the solder connections on R13, even if they look perfectly good.
Attached Images
File Type: png R13 1.png (37.3 KB, 81 views)
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Old 8th February 2013, 06:35 AM   #4
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Quote:
Originally Posted by ProTofik View Post
Hello.

I am measuring about 13v of DC on this channel's output (measured from P2).


Sorry for my english
I missed that one-
WARNING: don't connect your HD800 yet. 13 VDC is too much. List the issue on The Objective2 (O2) Headphone Amp DIY Project
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Old 9th February 2013, 09:55 PM   #5
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Quote:
Chk the input socket, it might be faulty or dry soldered.
Use one end of i/p pin & chk for continuity of the i/p socket(blue)
I checked it. It's all ok.
Quote:
Try reheating the solder connections on R13, even if they look perfectly good.
Done. It didn't help.

I did follow the NwAvGuy's trobule shooting guide once more and here are the results.

At Initial DIY Testing section I am failing Check The Raw DC Voltages part. Here are the results:
Click the image to open in full size.

After that I jumped to Troubleshooting Problems section and I think there is something wrong at Negative Unregulated Supply part. This is what I got:

Click the image to open in full size.

Anymore ideas?

Last edited by ProTofik; 9th February 2013 at 09:59 PM.
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Old 10th February 2013, 12:54 AM   #6
agdr is offline agdr  United States
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Quote:
Originally Posted by ProTofik View Post
At Initial DIY Testing section I am failing Check The Raw DC Voltages part.
Yep, that is the other thing that will cause the problem, one power supply rail missing. No luck on viewing your images - first comes up the size of a postage stamp and I can't get the second to open at all - but check the voltage between ground (the metal shell of the gain switch) to pin 4 of one of the NJM4556 output chips (U3 or U4). Then measure between ground and pin 8. Be very careful not to short between the pins with the meter probe.

You should be getting close to -12Vdc on pin 4 and +12Vdc on pin 8 with the AC adaptor plugged in and the O2 turned on. If one of those voltages is missing, do the same tests between ground and pins 4 and 8 of U2, the NJM2068. If you get +/-12Vdc there but are missing one voltage on the output chips then one of your mosfets is not turning on.

Last edited by agdr; 10th February 2013 at 12:58 AM.
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Old 10th February 2013, 01:29 AM   #7
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Thanks for reply. I will check it tomorrow.
I will also reupload missing attachments tomorrow as I don't have an access to my PC now.
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Old 23rd February 2013, 09:27 PM   #8
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I've attached the files that were currupted in previous post.
Quote:
but check the voltage between ground (the metal shell of the gain switch) to pin 4 of one of the NJM4556 output chips (U3 or U4).
U3 - Pin4 = -16.61V
U3 - Pin8 = 11.71V

U4 - Pin4 = -16.63V
U4 - Pin8 = 11.71V
Attached Images
File Type: jpg 1.jpg (291.0 KB, 33 views)
File Type: jpg 2.jpg (327.0 KB, 35 views)
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Old 23rd February 2013, 09:52 PM   #9
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With the wall adapter plugged in, but the O2 turned off, measure the voltage across C7. It should be close to -12VDC. If it isn't, check that U6 is installed correctly, and that everything from J1 to D5 is as per the schematic.
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Old 23rd February 2013, 09:58 PM   #10
agdr is offline agdr  United States
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Quote:
Originally Posted by ProTofik View Post
I've attached the files that were currupted in previous post.


U3 - Pin4 = -16.61V
U3 - Pin8 = 11.71V

U4 - Pin4 = -16.63V
U4 - Pin8 = 11.71V
Those -16.6Vdc numbers on the Pin4's are a problem. Check the voltage from the banded end of diode D5 to ground (metal shell of gain switch) and see what you get. Should be -12.0Vdc +/- 0.3Vdc or so. If you are getting -16.6Vdc then either your negative voltage regulator (U6) is shorted, or more likely you have a solder bridge between the input and output pins on U6. On that chip (MC7912) the input and output pins are right next to each other and would be easy to short.

Use a magnifying glass to check - I've found it is nearly impossible to see a short there without using one.

Edit: looks like sofaspud and I were composing at the same time - and we agree on where your problem is. See what you find there.
Attached Images
File Type: png U6 short 1.png (51.5 KB, 9 views)

Last edited by agdr; 23rd February 2013 at 10:01 PM.
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