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Old 28th November 2006, 08:52 AM   #21
Ovation is offline Ovation  United Kingdom
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Well, I spent another load of hours last night looking at this amp. I've figured that most of the protection circuit components are directly in front of the Fan except a few near the front soft-start relay.

I've pulled all the small electrolytics out (not the one on the channel inputs though).. They all seem to test okay on my DVM. There's a 1000V 47uF cap which reads about 43uF on the meter - I guess that's slightly low, but do you think it could really be a problem. All the other little 25/35v 47uF caps read about 47uF on the meter.

I can't find any diodes or transistors which are short or open circuit, and I've removed Q45 (TO220) and tested it out of the board and it works fine.

I also pulled the VU Panel from the front of the amp and checked what I could on there. I can't find any immediate fault on this - I think the VU takes its input after the output relay so I guess it makes sense that it doesn't respond to input, but why to the first two LEDs always light??

You guys have been a massive help so far - I'll keep going at this as a soultion can't be far away.

I'd really appreciate any other suggestions you have - Particularly on other transistor fault conditions to look out for, and the vaule of that 1000v cap as above.

Many Thanks
Jonathan
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Old 28th November 2006, 09:39 AM   #22
Netlist is offline Netlist  Belgium
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A 43F cap needs to be replaced. I'm not saying that this will solve the problem but if nothing else can be found, it's worth a try.

/Hugo
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Old 28th November 2006, 10:39 AM   #23
707dave is offline 707dave  United Kingdom
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hi,
Is the amp oscillating at hf, might explain the bar graph leds on. Check the Zobel network components as o/c can cause R's or C's can cause amp to oscillate in MHz region.
have you continuity between relay driver Transistor emitter and ground? Ie no broken traces on pcb
Check AC is getting to pcb via thermal switch ( Norm Closed) , as this is needed to get cct out of start up delay.
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Old 28th November 2006, 10:44 AM   #24
Ovation is offline Ovation  United Kingdom
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I'll go out to Maplin at lunch time - Hopefully this Cap is common enough for them to stock...

Just a really quick sanity check here: I have never yet attached a load to this amp - There's no way it would go into protect because of open circuit speaker terminals. Is there?

Perhaps I should just attach a speaker and check this :-)
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Old 30th November 2006, 02:57 PM   #25
Ovation is offline Ovation  United Kingdom
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Hi Guys,
I spent another little while on this amp a couple of days back. I still havne't replaced any caps, but I'm soon to do an order of some bits and I'll probably replace all the small electrolytics for the fun of it.

I looked for Oscillation on the amp - Interestingly I discovered that if I input a 1KHz tone, then I can see the amplifier signal on both the internal circuit and also the Red speaker poles (I've just had a thought - Do the relays switch on the negative/black? That might exlain it!) - The relays definitely don't click over.

If I run the amp with no input signal I can see a very small oscillation on one of the channels - It's <5mV peak-peak and I never figured out the frequency - I'll have to check my TimeBase and calculate it.. I'm considering that the reading on the scope could possibly be spurious interference.

I'm really stuck now - I just can't find anything that isn't reading normal ...

707Dave - Do you happen to have a higher resolution diagram of the prot circuit? (If necessary I can send you some money for a hard copy) - I think I've figured out the Q numbers for the transistors but I really can't see what values the other components are meant to be, or where they are :-)

AC *is* getting to the Thermal Switch (70v I think), and the switch is closed.

Forgot to test Q45 Emitter -> Ground , I'll do that and post back.

I've spent so much time on this amp I am determined to fix it now. I'll get those caps ordered soon but I'm not convinced that they will fix it.

Many Thanks
Jonathan
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Old 6th December 2006, 11:01 PM   #26
707dave is offline 707dave  United Kingdom
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Here are component values for protection cct. Hope they help.

D7, D8, D9, D11, D30, D12 = 1N4004
D10, D11 = 1N4148
Q20, Q22, Q23, Q26 ,Q46 = BF422
Q21, Q24 = BF423
Q45 =2SA968
Z7 =9V1
Z12 = 6V8
R63, R64, R66, R67 = 47K
R62, R65, R149, RMOD1, R78 = 100K
R69 = 24K
R148 = 39K
R158 = 120R
R68 = 330R /4W
R141 = 10K /1W
R61, R151, R152 = 10K
C37 = 680Nf
C38, C39 = 100Uf/16v
C49 ?
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Old 7th December 2006, 08:33 AM   #27
Ovation is offline Ovation  United Kingdom
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Hi Dave,
Thanks for that information - I've not had a chance to look at the Amp this week - I've been fixing a couple of TVs and also started looking at an Active Sub. Hopefully I'll get a chance to work on the C-Audio amp this weekend.

As I mentioned, I'm looking at a Mordaunt-Short Active Sub (with guts made by 'audix') - It uses a pair of Power Amp ICs to drive two separate woofers. The same signal is fed into both and I can see using the scope that the input is reaching the devices and that they are correctly powered, but no sound is coming out and I can measure -2vdc across each output (The speakers are disconnected at present). I'm planning next to remove one of the ICs and test, then swap to the other one and see if one has failed and is bringing the other down - Anyone got any better ideas?

Many thanks
Jonathan
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Old 19th June 2007, 01:40 PM   #28
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Default RA fault

Hello Jonathon,

The main reservoir capacitors in this series of amps had a plastic cap on top which tended to crinkle up giving the impression that the caps had failed, in fairness during my tenure with C Audio (10 years)I changed very few due to venting.

The unit is in protect, if you power it up and inject a sinewave (off load, no speakers connected) do you get normal operation of the LED bargraph on both channels, if yes then the amp has a protection fault.

if you have 2SK135 and 2SJ162 mosfets it is unlikely they have failed as they are very robust and usualy in this amp failure is evident by a hole or burn mark on the the can of the device.

I can send you circuit diagrams for this range of amp along with servicing details if you send me your email details to

lee.basham@lj-electronics.com

or you can call me 07768 551482 and i can probably talk you through fault finding to component level.


thanks
Lee Basham
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Old 3rd November 2011, 04:59 PM   #29
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Hello All, I am a new Member at DIYAudio though I have been reading the site for many years - congratulations on a excellent forum!

I have a faulty C-Audio RA2000 exactly as described in this thread that I am very keen to repair as it is part of a 3-way set.

After much searching I am unable to find schematics for this amplifier and would greatly appreciate any assistance in obtaining them.

As per Lee's last post, I seem to have a protection fault but have received no reply from his quoted email address, though obviously this posting was quite some time ago.

Once again, congratulations on an excellent forum that I have always found to be informative & friendly.
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Old 6th November 2011, 10:49 PM   #30
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What have you checked so far?
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