Audiolab 8000A blowing fuses - REPAIRED!!! - diyAudio
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Old 28th July 2012, 10:10 AM   #1
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Lightbulb Audiolab 8000A blowing fuses - REPAIRED!!!

So, I had a late model 8000a brought in for repair. Customer suspected a transformer problem, as it kept blowing the main fuse, but I was more worried about the output devices.
A quick sweep of the underside of the board showed that these and the pre-drivers were all ok, but something about the Collector readings didn't seem right; one rail floated but the other was somehow clamped.
Ha!
Took me a minute to find it, underneath the PSU wiring, but when I checked the bridge rectifier I found two pins short-circuit.
Why did they use that little piece of cp? And then leave it with insufficient cooling?
Anyway, just my little addition to the knowledge base.
BTW, repair not yet completed. I dont fancy taking that 3D wiringloom apart, so I'm just going to leave the LPoC (edit; little piece of cp) in situ and just wire a bigger BR around it.
cw
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Old 29th July 2012, 07:31 AM   #2
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Hmm...Sounds like the rectifier could also be a fast fuse!
Seriously though, what current rating is the original bridge? Sizing varies inordinately and many Japanese 60W+ stereos satisfactorily used only 3 amp diodes for many years but I have seen enough cheap amplifiers from everywhere with only 1.5 amp bridges, yet DIYs fear that 35A may not be big enough for their 10W JLH amps.
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Old 29th July 2012, 02:05 PM   #3
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LOL, Master fuse.
The LPoC was just a SIL 3-4A thing. Plus it was wrapped by PSU wiring looms and the supply caps. Put a big metal 10A jobby in there. I'll post some pics.
I think it needed a bigger one; the circuit board is SCORCHED on the power section from years of abuse.
And does size matter? Well, you can never have enough power...
cw
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Old 29th July 2012, 02:16 PM   #4
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Those pics
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Old 29th July 2012, 10:54 PM   #5
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Thanks for the pics. Ouch! scorched alright - deep fried even. It appears that the whole output stage is designed to run on the very limit of component dissipation. Clever design but doesn't win the quality cigar in the consumers perception, I think
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Old 29th July 2012, 11:05 PM   #6
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Quote:
Originally Posted by Ian Finch View Post
Thanks for the pics. Ouch! scorched alright - deep fried even. It appears that the whole output stage is designed to run on the very limit of component dissipation. Clever design but doesn't win the quality cigar in the consumers perception, I think
you are right! there are many diy amps here that will "kill" this amp in performance, design and quality. I guess it is bussines and the companies just see it this way. that is why I went for a DIY amp instead...I love it!!!
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Old 1st March 2016, 02:34 PM   #7
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Originally Posted by lanchile View Post
you are right! there are many diy amps here that will "kill" this amp in performance, design and quality. I guess it is bussines and the companies just see it this way. that is why I went for a DIY amp instead...I love it!!!
Couldn't agree more!!!
cw
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