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Old 16th March 2012, 07:29 PM   #2241
Fsatsil is offline Fsatsil  United States
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Originally Posted by ethanolson View Post
@Fsatsil, you gotta fix the date stamp on your camera.
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Old 16th March 2012, 07:34 PM   #2242
T2T is offline T2T  United States
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Originally Posted by Willakan View Post
Those JDS Labs front panels sure are purdy...
Yes, it does look nice. Though, I received a new panel made from bamboo in the mail yesterday with my 2nd O2 amp. The bamboo panel with the black case looks sweet!

I'll try to get a picture posted this weekend so you can see if you agree.
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Old 20th March 2012, 08:30 AM   #2243
BlueRob is offline BlueRob  Mexico
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Default Start-up Problem

I completed the O2 and passed the initial checks with no apparent problem, but on the initial test drive it was pretty obvious that my right channel was awfully distorted while the left seems to be OK.

Would the short already mentioned between via hole and gain switch near R21 cause this?

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Old 21st March 2012, 04:18 AM   #2244
BlueRob is offline BlueRob  Mexico
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Forget about my last post...I was frustrated...still am tho.

We have pinned down the problem....a faulty board
It seems that the path between R16 and U1 pin 6 is the culprit, as result we had -10.6 volts or so in that pin.

What to do next? We can add that R16 and C19 cap off the board to overcome the issue but to be honest I don't like it, it does the job but I hate to have components floating around.

I bought the PCB from JDs Labs, I have thought on returning it (if that can be done) but its already populated with all the bells an whistles
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Old 21st March 2012, 05:10 AM   #2245
agdr is offline agdr  United States
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Quote:
Originally Posted by BlueRob View Post
but on the initial test drive it was pretty obvious that my right channel was awfully distorted while the left seems to be OK.

Would the short already mentioned between via hole and gain switch near R21 cause this?
That does sound like the gain switch problem. It affects the right channel and causes distortion. Just take a small (jewelers) screwdriver and carefully bend the two tabs on the switch that are over the via back under the switch. The shell of the switch is soft metal and bends pretty easily. The tabs can look like they are not touching the via but actually are.

As for your voltage on U1 pin 6 (pin 6 is on the left channel), pull U1 out of the socket and check if one of the pins bent underneath U1 rather than going into the socket properly. Easy to happen. The pins on chips are bent out slightly to stay put in automatic insertion equipment. I always place an IC on one side on an anti-static bag and carefully roll the pins a few degrees so they are exactly perpendicular to the body, then repeat on the other side. Goes right in the socket properly that way.

If you don't have any bent pins on U1, what are the voltages from all 8 pins to ground (the metal shell of the gain switch) with nothing plugged into the input jack and the gain switch not pressed in?

Last edited by agdr; 21st March 2012 at 05:17 AM.
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Old 21st March 2012, 06:02 AM   #2246
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What to do next? We can add that R16 and C19 cap off the board to overcome the issue but to be honest I don't like it, it does the job but I hate to have components floating around.
Sounds like an exacto knife and jumper wire are needed.
And an ECO.
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Old 21st March 2012, 07:35 AM   #2247
BlueRob is offline BlueRob  Mexico
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Originally Posted by agdr View Post
That does sound like the gain switch problem. It affects the right channel and causes distortion. Just take a small (jewelers) screwdriver and carefully bend the two tabs on the switch that are over the via back under the switch. The shell of the switch is soft metal and bends pretty easily. The tabs can look like they are not touching the via but actually are.

As for your voltage on U1 pin 6 (pin 6 is on the left channel), pull U1 out of the socket and check if one of the pins bent underneath U1 rather than going into the socket properly. Easy to happen. The pins on chips are bent out slightly to stay put in automatic insertion equipment. I always place an IC on one side on an anti-static bag and carefully roll the pins a few degrees so they are exactly perpendicular to the body, then repeat on the other side. Goes right in the socket properly that way.

If you don't have any bent pins on U1, what are the voltages from all 8 pins to ground (the metal shell of the gain switch) with nothing plugged into the input jack and the gain switch not pressed in?
I did check for continuity between the gain switch body and the via hole (bottom of PCB) and they do not appear to be in contact with each other.
To be on the safe side IŽll bend the legs *** suggested.

After that IŽll try to describe briefly what we did, what I recall and hope IŽm not mixing the results from this morning tests.

We checked the proper sitting of U1 with its socket and all legs were bent prior the mounting in the socket, we even tried an different IC, same result. After that we started checking for resistance... between pin2 and pin1 we got 1.5K witch matches R22, but when we checked between pin 6 and 7 we didnt get any reading, we should have measured the 1.5k from R16, we checked the solder and the resistance itself out of the board and was OK.

After that we "bypassed" the board by soldering one end of the resistance directly to the IC pin6 and the other end to the board (yes we leaved out C19 out of the game with this test) , mounted the IC in its socket an voila! the -10 volts did not appeared in readings anymore.

With the above tests we concluded that some how the path between R16 and pin6 of U1 was the problem. We cant think of any other reason that could have caused the problem or that could have escaped the tests we did. The only thing that comes to mind is a non visible solder bridge somewhere but I cant figure out where a short would develop the symptoms and evade the test we did.

At some point we did check all the voltages from U1 pins and seemed OK, cant recall them now but tomorrow will try to recheck them and post the results....maybe you guys can help us to find a different outcome.

BTW I talk in plural since APASSGEAR (aka my father) old time member in the forum has help me a lot with the project.
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Old 21st March 2012, 12:50 PM   #2248
agdr is offline agdr  United States
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It would be relatively rare, but you may be right about a PCB problem there. The PCB trace going from U1 pin 6 out to R16 and C19 is on the top of the board, partially underneath the U1 socket. The trace relies on a through-hole at pin 6 to connect the bottom to the top of the board. Plated through holes can be bad, either break or not get fully plated in manufacture.

The first thing to try is to re-heat the solder joint on pin U1 pin 6 if you haven't already. If that doesn't do it you can test easily enough. Pull U1 out of the socket. Then with your ohmmeter on a low ohm range put one lead on the bottom of the PCB at pin 6 and the other on the end of R16 (on the top of the PCB now) closest to the board edge on the top. That should be nearly 0 ohms. If not the through-hole is bad and/or that hidden trace under the socket is broken.

Like sofaspud says you can do a fix with a jumper wire to the IC pin. Not pretty, but it works.

Last edited by agdr; 21st March 2012 at 01:09 PM.
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Old 21st March 2012, 12:55 PM   #2249
dixter is offline dixter  United States
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Quote:
Originally Posted by BlueRob View Post
We have pinned down the problem....a faulty board
It seems that the path between R16 and U1 pin 6 is the culprit, as result we had -10.6 volts or so in that pin.
Can you post a picture of the problem... is this a short or an open... I've got several boards I'd like to inspect prior to putting the parts on them...

Thanks
db
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Old 21st March 2012, 05:06 PM   #2250
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Originally Posted by agdr View Post
That should be nearly 0 ohms. If not the through-hole is bad and/or that hidden trace under the socket is broken.
If it's a tricky via, it would be easy enough to flow a little solder into it - an option for one who wants to avoid conspicuous repairs. I could understand how someone might prefer not to trust that, though.
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