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Looking for some input on a problem with one of my Legato 3.1 boards - with buffers.
I built up two Legato 3 boards for my dual mono setup. One board adjusted DC offset out perfectly both balanced and SE. The other boards adjusted DC out perfectly on the balanced outputs but the right SE output shows 13.5v between GND and SE R, the trim pot has no effect - the pot measures ok, the board has been checked carefully for errors etc.
Any ideas what to check?
Also presume when using dual mono the headphone output can be used for the buffered balanced out? Presume no need to change anything else for this configuration?
Cheers,
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Sounds like a short or a dry solder joint. Post pics.
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Also make sure you can get the wiper of the SE pot to the center. Measure resistance from the wiper to each end. Make sure you can get it to be close to even on both sides
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And yes to your question about using the HPout as balanced out in Dual mono mode. :)
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How do you post pics?... Measured pot at at 0.912 kohm and 0.923kohm The jumpers were missing for J1 - J4 so i used wire; this is clear of the epoxy coating on the pcb though. Thanks, Luke hisense attached the following image(s):  IMG_1897.jpg (233kb) downloaded 281 time(s). IMG_1898.jpg (235kb) downloaded 280 time(s). IMG_1899.jpg (177kb) downloaded 280 time(s). IMG_1900.jpg (232kb) downloaded 279 time(s). IMG_1901.jpg (237kb) downloaded 281 time(s).You cannot view/download attachments. Try to login or register.
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Touch up the solder (top and bottom) around R19/20 R35/36 R23/24. Also check around the op-amp socket.
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Re made the solder joints and soldered top side as well. Also re soldered the op amp socket. Swapped op-amp for part from working board - no change. Still 13.5 between SE R and Gnd.
Also measured 13.5 at one of the pads at J6 if that helps - could you advise some measuring positions to help determine where the fault is?
Have compared in circuit component values between left (good side) and right and cant find any unusual values on the faulty side.
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Measure the voltage at pins 1, 2 and 3 of the op-amp to GND. Also check for any shorts to either rail or to GND at all of the resistors I mentioned above with your DMM (with power off). Also check for any shorts across any of pins of the op-amp. Note: One pad of R24 will be connected to GND, the other should not be. Especially check for a short (with your DMM not visually) between pin 3 and 4 of the op-amp. Edited by user Saturday, May 21, 2011 5:56:30 AM(UTC)
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It also would not hurt to touch up the pins of the LME49600(IC3). It could be (but not likely) that it is not making good contact with a pad. Edited by user Saturday, May 21, 2011 6:13:01 AM(UTC)
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Hi Russ, Problem solved - i went through the checks for shorts and none found; pin 1 read -14.5v, pin 2 6.43v and pin 3 5.58v after re soldering all legs of IC3 it worked perfectly. Must have been a dry joint at IC3
Thanks for the prompt support,
Cheers,
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Rank: Administration
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Good job tracking it down!
Very glad all is well now. I hope the rest goes smoothly. :)
Keep us posted.
Cheers!
Russ
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