C-Audio SR-707 Protect Issue |
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qwerp
Registered User Joined: 01 March 2019 Status: Offline Points: 41 |
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thanks, I shall give it a go later on I forgot the mention there are little variable pots ( Phillips screw driver type) on each channel board and they had oxidisation on them, like white crystals or fluff. Im not sure if this made its way onto the contacts |
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qwerp
Registered User Joined: 01 March 2019 Status: Offline Points: 41 |
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Hi yes there is amplification on both channels and sounds clean too I was using an old cheap plastic speaker ( not sure of the ohms) wasn't all that loud. So it is the protection circuit. Oh my, I shall have to lever it out and have a look. : / : ) |
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7199 |
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Yes - I was going to suggest this - but with a sig gen & oscilliscope! The best way to see if it is just a faulty protection circuit - or if there is more going on, eg high frequency instability/oscillation on the o/p. A simple multimeter check won´t pick that up. |
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simonp1100
Young Croc Joined: 01 September 2008 Location: Bristol Status: Offline Points: 1103 |
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I suggested this as i assumed he does not have this type of equipment and would give a quick way of finding out if the protection circuitry is faulty or not and if sound is coming out whether it is distorting etc.
Edited by simonp1100 - 03 March 2019 at 1:24pm |
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qwerp
Registered User Joined: 01 March 2019 Status: Offline Points: 41 |
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owch, i did the test with a speaker, with 44mv DC present on one chn and 83mv DC on the other chn. (These DC readings were taken before when with nothing connected in or out.) I do not have an oscilloscope unfortunately. Edited by qwerp - 03 March 2019 at 1:32pm |
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simonp1100
Young Croc Joined: 01 September 2008 Location: Bristol Status: Offline Points: 1103 |
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Did it work ??. The DC offset for these amplifiers are normally around + or - 10mv so the readings are a bit high and maybe need adjusting (after a warm up for about 10-15 minutes).
Edited by simonp1100 - 03 March 2019 at 1:34pm |
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qwerp
Registered User Joined: 01 March 2019 Status: Offline Points: 41 |
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yes copy of post above > yes there is amplification on both channels and sounds clean too I was using an old cheap plastic cased speaker ( not sure of the ohms) wasn't all that loud. So it is the protection circuit. Oh my, I shall have to lever it out and have a look. : / : ) Edited by qwerp - 03 March 2019 at 1:33pm |
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7199 |
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Yes - I noted the 'scrap speaker' comment! I have a few of those around the place as well for 'real life' tests. Sometimes circuits will behave differently under load. |
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qwerp
Registered User Joined: 01 March 2019 Status: Offline Points: 41 |
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if there is hf oscillation confusing the protection circuit could i trick the protection circuit by disconnecting something ( the feedback?)
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simonp1100
Young Croc Joined: 01 September 2008 Location: Bristol Status: Offline Points: 1103 |
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Glad we are getting there. You may need to take the board out and start measuring the components on the protection circuit. The boards come out easily as the are just on plastic PCB spacers (don't forget to push the small plastic release pin in before the board passes past the pillar). |
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7199 |
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Ok - at least you now know. Another question: are the output devices getting very warm? That would be a sign of high frequency oscillation - fairly common with MOSFETs. (Or bias too high.) |
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qwerp
Registered User Joined: 01 March 2019 Status: Offline Points: 41 |
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Thank you very much I shall try and fault find the protection circuit later on : )
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