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C-Audio SR-707 Protect Issue

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qwerp View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote qwerp Quote  Post ReplyReply Direct Link To This Post Topic: C-Audio SR-707 Protect Issue
    Posted: 01 March 2019 at 6:28am
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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Post Options Post Options   Thanks (1) Thanks(1)   Quote njw Quote  Post ReplyReply Direct Link To This Post Posted: 02 March 2019 at 8:48pm
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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Post Options Post Options   Thanks (1) Thanks(1)   Quote simonp1100 Quote  Post ReplyReply Direct Link To This Post Posted: 02 March 2019 at 9:33pm
[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    Clap
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Post Options Post Options   Thanks (1) Thanks(1)   Quote njw Quote  Post ReplyReply Direct Link To This Post Posted: 02 March 2019 at 9:57pm
Originally posted by simonp1100 simonp1100 wrote:

[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.
 

 Metal Oxide Semiconductor Field-Effect Transistors....

...Or am I missing something? Confused
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Post Options Post Options   Thanks (1) Thanks(1)   Quote simonp1100 Quote  Post ReplyReply Direct Link To This Post Posted: 02 March 2019 at 10:33pm
Originally posted by njw njw wrote:

Originally posted by simonp1100 simonp1100 wrote:

[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.
 

 Metal Oxide Semiconductor Field-Effect Transistors....

...Or am I missing something? Confused


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. LOL
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Post Options Post Options   Thanks (0) Thanks(0)   Quote qwerp Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2019 at 12:53am
Originally posted by simonp1100 simonp1100 wrote:

[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    Clap



Thank you very much Smile

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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Post Options Post Options   Thanks (1) Thanks(1)   Quote Xoc1 Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2019 at 1:29am
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote qwerp Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2019 at 2:44am
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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Post Options Post Options   Thanks (0) Thanks(0)   Quote qwerp Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2019 at 3:23am
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Edited by qwerp - 03 March 2019 at 3:25am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote qwerp Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2019 at 3:25am
Originally posted by Xoc1 Xoc1 wrote:

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,


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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Post Options Post Options   Thanks (0) Thanks(0)   Quote qwerp Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2019 at 3:34am

Originally posted by Xoc1 Xoc1 wrote:

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,



there is only 0.044v DC on the other side.

I think the three soft start relays must be working if the protect circuit has its power.

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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Post Options Post Options   Thanks (0) Thanks(0)   Quote qwerp Quote  Post ReplyReply Direct Link To This Post Posted: 03 March 2019 at 7:10am

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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