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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Posted: 01 March 2019 at 6:28am |
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Hello I have a power amplifier C-Audio Sr707 The protect LED comes on when turning on it on. The fans come on too. but it does not amplify. it all looks clean inside, the glass fuse inside is o.k. I wonder does anybody know what the fault might be? Could it be a relay in this instance? Thank you for any help you may offer..
Edited by qwerp - 01 March 2019 at 6:35am |
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njw
Old Croc Joined: 26 March 2010 Location: S. Wales Status: Offline Points: 2574 |
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It could be a relay or the soft start resistor, they usually fail for a reason though, more often than not blown output transistors.
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simonp1100
Young Croc Joined: 01 September 2008 Location: Bristol Status: Offline Points: 1110 |
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[QUOTE=njw] It could be a relay or the soft start resistor, they usually fail for a reason though, more often than not blown output transistors.
The output devices are MOSFET'S (2SJ50 & 2SK135) NOT transistors. Check that all 3 relays on the soft start PCB board are o.k. (not burnt & are opening and closing) and also check on each driver PCB board the 27K 1 Watt resistors (R14 & R50) as they have a tendency to go open circuit due to heat and age. The other thing you could check is to see if there is any DC offset voltage (above 1 volt) on each channel output (before the protection relays), if there is, this would give you an ideal which channel is faulty. Good luck Simon
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njw
Old Croc Joined: 26 March 2010 Location: S. Wales Status: Offline Points: 2574 |
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Metal Oxide Semiconductor Field-Effect Transistors.... ...Or am I missing something?
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simonp1100
Young Croc Joined: 01 September 2008 Location: Bristol Status: Offline Points: 1110 |
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No, but there IS a difference between the two and i think that MOSFET would have been more of a correct & accurate statement rather than transistor.
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qwerp
Registered User Joined: 01 March 2019 Status: Offline Points: 41 |
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Thank you very much I tested the 27k 1w resistors called R24, R34, & R50 on my pcb, they all tested o.k and looked fine. fuse 1 is o.k on soft start board. i can de solder and remove the soft start board, id be able to remove the relays as i have the de-soldering machine but there are no codes fotr replacements. I could test them, but am not 100% sure with 230v (I normally use 9v on breadboards) it looks like the mains is rectified and that high voltage dc is used to trigger the relays. As you can tell my knowledge is limited so might be best if I change the relays and see if that remedies the fault. i wonder do you know the part number? thanks again : )
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Xoc1
Registered User Joined: 15 October 2012 Location: Devon UK Status: Offline Points: 397 |
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Check the amplifier for a DC offset before the output relay, The body of the output mosfets to the negative speaker binding post is a handy place to measure this. No point sweating over the relays if they are just doing their job and stopping your speaker from being damaged,
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qwerp
Registered User Joined: 01 March 2019 Status: Offline Points: 41 |
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hi thanks for your reply. Do you mean when the amp is on and the protect light is stuck on (fans run) to connect a multimeter (set to dc) and probe the two points in the photo below? thought id check to be sure as i am just a novice. http://oi64.tinypic.com/xp30x4.jpg thanks
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qwerp
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Edited by qwerp - 03 March 2019 at 3:25am |
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qwerp
Registered User Joined: 01 March 2019 Status: Offline Points: 41 |
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I forgot to quote your email i am not sure if that makes a difference with notification. so posting again. 0.083v is what i see on my meter. I hope that is good? thanks for any further help
Edited by qwerp - 03 March 2019 at 3:26am |
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qwerp
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there is only 0.044v DC on the other side. For the two output relays to come on, does the protect LED not need to go off at the same time? So, perhaps it is unnecessary to check the output relays whilst the protect light is still remaining on? thanks again Edited by qwerp - 03 March 2019 at 6:53am |
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qwerp
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Here are some schematics of the protect circuit with its LED , just under the LED are two lines Labelled "CONT" and "GND"(orange & pink) which connect to the output relays 2nd picture below is the output relay area and the soft start also. Right click "view image" for a closer look. Thanks for any help. Edited by qwerp - 03 March 2019 at 7:11am |
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