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Old 12th December 2012, 03:03 PM   #1031
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Quote:
Originally Posted by westers151 View Post
...what exactly is the small signal area that you mention in your post. Is it the LM318?
Yup, the area on the board that is shielded by the ground plane, including the input connector block, input cap, input filter, feedback network, compensation networks, Howland resistor networks, and LM318 opamp.
Some of these nodes have large voltage swings, so 'small signal' is a bit of a misnomer.
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Old 12th December 2012, 08:02 PM   #1032
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Thanks, I'll check those.
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Old 15th December 2012, 04:34 PM   #1033
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Still no joy - I've swapped R14 and R21 for the values discussed, checked for solder bridges using a magnifying glass (none found), and double checked all the capacitors. The board refuses to work.
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Old 15th December 2012, 11:05 PM   #1034
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westers151
I would verify the build instructions against what you've already placed. From reading in this thread, the percentage of builders who misplaced or left out components is more than four times those that claim a defect and many of those who discovered their error initially suspected defect so that ratio may climb even higher.
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Old 16th December 2012, 08:54 AM   #1035
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I'm not claiming a defect (I have one channel working and it sounds fine), I just don't understand why this one isn't working.

I did follow the build instructions to the letter, however I have gone back (yet again) to verify all the components, and they are fine. However, as a result of doing that, the board is now broken; I had to lift some resistors to double check the values, and as a result of doing that I have lifted the pads on one of them.

Linux Guru - Do you have any of your boards for sale? I don't fancy doing the surface based soldering on Clave's (although I may have to if there are no through hole boards left).
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Old 16th December 2012, 12:14 PM   #1036
udailey is online now udailey  United States
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Find your bad pad. Find the trace associated with it. Scrape the soldermask off of the trace. Solder onto the scratch instead of the pad.
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Old 16th December 2012, 12:30 PM   #1037
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There is no trace on the one with the lifted pad - it's R14, and the leg that isn't connected to a trace.
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Old 16th December 2012, 12:32 PM   #1038
udailey is online now udailey  United States
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Also I have started doing surface mount soldering and I find it very easy. Yes a magnifying glass is helpful. Just tin one pad then grab part with Tweezers and touch part to tinned pad while touching both with the iron. Use a lot of flux on parts with more than two legs to avoid solder whiskers between two legs. With through hole we have to bend leads, place component, bend again, flip board, trim. SMT is just tin pad, hold in place, heat, solder other side. Not bad.
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Old 16th December 2012, 12:33 PM   #1039
AndrewT is offline AndrewT  Scotland
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Maybe the trace is on the other side of the PCB.

The resistor must have a purpose and for that it must be connected at both ends to the circuit.
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Old 16th December 2012, 01:32 PM   #1040
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Yes, it's on the top of the board under R23, but hidden by R23 when that is installed.

However, what is more interesting is the behaviour of my soft start when the "faulty" board is not connected to the power.

When the "faulty" board was connected to the power, I could see the operation of the two relays in the soft start circuit. What I noticed was the delay relay didn't pull open all the way - it only moved a little, but obviously enough to power on one of the boards.

With the "faulty" board removed from the power, the delay relay in the soft start now opens fully, and with a much louder click.

However, power is getting through to the "faulty" board (when I connect it all back up), as I've measured the correct rail voltage for both V+ and V-, as well as the 12V for the LM318.
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