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Old 2nd October 2011, 12:23 PM   #41
diyAudio Member
Join Date: Dec 2007
Hi, the soft-start / protect circuit is petty much a 47R / 23W Ceramic (or 50W Alu) resistor with a relay across it.
The soft-start is just an R-C to create the switch on delay. This feeds relays to bypass the soft start resistor, and to connect the speakers.
The same relays are used to shut the amp down if it goes faulty.
Its most likely that someone has disconnected this because the amp was 'stuck in protect'.
This is a common fault with the RA's, often due to the design. The sensitive fault detect transistors are right next to the fan, which means they get covered in damp fluff.
You need to clean this area with a toothbrush / alcohol.

this site is awesome... the C-Audio circuits are on here - with a detailed description of the protection circuit...
Free Diagrams, Schematics and Service Manuals

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Old 3rd December 2012, 09:47 PM   #42
diyAudio Member
Join Date: Dec 2012
Location: gateshead
Default ra 3000 blowing fuses


i have a bad problem with my c audio ra3000. it keeps blowing every fuse in and out of the unit instantly upon power-up. i suspect the caps in the psu to be dry. but i haven't gone further than the toroid which seems to be ok. but im not ruling it out.

the amp has been really heavily used in a night club before i had it. i used to manage the sound system in there and know what went on. every time i went in there everything was turned up to 11 if ya know what i mean.

it uses j50's and k135's which i haven't seen anyone mention on here yet. are these the original mosfets for this amp? could they just be shorted out?

like i say i havnt done anything apart from measure resistance and voltage on the toroid so anything is possible.

any help is appreciated. thanks in advance.

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Old 3rd April 2014, 03:39 PM   #43
diyAudio Member
Join Date: Dec 2009
Hi lee,
I need help to fix "C-Audio GB402 Amplifier"
I have a problem with one chanel of the above I trace a signal,with oscilloscope, up to the transistor base, next to 3 pin pot connector, but after that it is very difficult to follow the circuit due to the size of the PCB. Diodes and transistors look OK with multimeter diode measurement.
That's why I am looking for service manual or electronic circuit, if there is any available.
Best regards,
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Old 3rd April 2014, 10:54 PM   #44
burbeck is offline burbeck  United Kingdom
diyAudio Member
Join Date: Aug 2004
Location: Ratae Coritanorum
hi Pan
i have the information you require please email me
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Old 4th April 2014, 07:25 AM   #45
diyAudio Member
Join Date: Dec 2009
Hi Bob,

Thanks for your reply.
I appreciate if you can help.
As i mentioned on #43 post, I am looking for "C-Audio GB402 Amplifier" service manual or electronic circuit , if there is any available.
Best regards,
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