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One channel of my Buf32s is not working. I've tested the outputs (both channels) with an oscilloscope. I have used a CD track with a 1kHz signal and one channel shows the signal ok, as it should be. However the other channel shows no AC signal, instead appear 13.8Vdc between + and GND and -7.9Vdc between - and gnd. Seems clear that the analog part of the buff32 is failing . Could someone please help me? Since the scheme is not available I guess Brian and/or Russ would know with more certainty that may be failing. The configuration of the dac is very simple. I use spdif input and SE output (signal taken from + and gnd) and two Placid BP one per channel (+/-15V and 200mA supply current configuration) and one Placid for Digital (5.20V and 200mA supply current configuration) . Attached is a photo of the dac. [img]null[/img]  Edited by user Saturday, April 20, 2013 3:00:56 PM(UTC)
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Russ, I did measurements at the outputs of each opamp (no input digital signal) as you suggested:
LME49710: Vout = 3.3Vdc
LM4562: VoutA = -14.32Vdc -- VoutB = 1.65Vdc
OPA1632 (IC12): Vout+ = 1.65Vdc -- Vout- = 1.65Vdc
OPA1632 (IC11): Vout+ = 13.83Vdc -- Vout- = -7.94Vdc
No AC in any output.
I check all the supply voltages and was ok (+-15Vdc)
Regards,
Francisco
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My first guess is that IC11 is damaged and needs to be replaced.
IC14 could also be damaged, but this is less likely.
Cheers!
Russ
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Thanks Russ! I ordered the parts in order to replace the parts you suggested.
I´ll let you know when I do it and the result.
Regards,
Francisco
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Excellent. Also while you are poking around just double check all of the passives around IC11. Especially any through hole parts. Edited by user Monday, April 29, 2013 3:49:12 PM(UTC)
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To avoid any mistake on my part, could you tell me exactly what passive components should be checked and what value should be?
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I just meant solder joints around R49/R50(if installed) C47/48 R36/37 R40/R41 R34/35 R32/33 Edited by user Monday, April 29, 2013 11:43:10 PM(UTC)
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Hello again Russ,
After a long delay to get the parts, I replaced IC11 and seem that the reported failure was solved. The problem is that while I was checking all the voltages, something went wrong. First I noted the Vd from the Placid regulator fell from 5.25Vdc (without load) to 1.48Vdc (when connected to the Buf32s). Then I checked the ICs outputs and obtained the next values:
IC6 (LT1763 reg): Vout = 0.16Vdc
IC4 (LT176333 reg): Vout = 1.48Vdc
IC5 (LT176333 reg): Vout = 0.29Vdc
IC2 (LME49710): Vout = 0.160Vdc
IC14 (LM4562): VoutA = 0Vdc -- VoutB = 0.078Vdc
IC12 (OPA1632): Vout+ = 0.079Vdc -- Vout- = 0.079Vdc
I was wondering why the voltages in the right channel were near zero and rechecked all the ICs outputs. When I was measuring the voltage in the pin 6 (Vout) of IC3, at the same time, I accidentally touched the pin 7 (V+ = 15Vdc). Then I had a very bad feeling. When I returned to measure the outputs of the left channel ICs I found that all were near 0volts, as were the right channel.
IC3 (LME49710): Vout = 0.105Vdc
IC13 (LM4562): VoutA = 0Vdc -- VoutB = 0.053Vdc
IC9 (OPA1632): Vout+ = 0.053Vdc -- Vout- = 0.053Vdc
Seems I made the same mistake in both channels and this confirmed that a good pulse (not like mine) is essential to test those small ICs. I hope my experience help others…
Then I ordered a replacement for IC2 and IC3 and I have replaced them. But no changes. Could you help me again please?
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As the Vd from the Placid regulator fell from 5.25Vdc (without load) to 1.48Vdc (when connected to the Buf32s), I guess some device is sucking a lot of current. Then I decided to remove all the operational amplifiers progressively in order to see which is failing. I removed all the ICs except IC10 but Vd continues to give 1.48volt... Could be a regulator (IC4, IC5 or IC6) is failing?
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Yes something is likely shorted. It could be any active device on that rail including the DAC itself. Edited by user Sunday, May 26, 2013 6:55:53 PM(UTC)
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Also check the 100uF OS-CON caps for shorts. I have seen it before.
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Thanks Russ and Brian,
Russ I agree with you, but without having the scheme is very difficult for me to figure what element could be failing. Based in the measurements I gave you in the post#8, What do you think is more likely that this failing? (at this time I only have on the board the next active devices: the dac, IC10 and the three regulators). How could I exclude that the dac is failing (without remove it from the board)?
Brian, I´ll test the os-con caps too. (I assume I can test caps for short in circuit, without remove it from the board).
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