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Old 24th March 2005, 06:40 AM   #1
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Unhappy Onkyo M 508 Capacitor goo

First of all I am new to this forum and already it has helped me with this issue. Got the downloadable service manual for this amp from a post search. Thanks for the info.
I moved the amp the other day and noticed a brown hard goo under on the bottom cover. I researched the net for possible problems and found out about the 10,000 uf caps that are a known problem. I opened the amp and that is the area where the problem seems to be.
The amp is working ok, but I don't like when my stuff is not right.
Lookin around for the caps has taught me these caps are not real easy or cheap to come by.
Has anyone done this repair? Where did you get your caps? Costs?
What should I know in advance before changing them out? (ESD and normal percautions I am aware of)
Onkyo USA has the caps for about $300.00 for the 8. Different part number so I suspect they upgraded the part for this issue.
Seems like a straight forward job, but I like to ask others that have done something for advise to make a job smooth if possible.
Thanks in advance for any info.
J.T. Stanton
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Old 24th March 2005, 10:56 AM   #2
K-amps is offline K-amps  United States
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JT,

Any cap of similar dimensions will work. As you know to look for the ESR/ Cap/ voltage rating. Chances are for the same size, newer caps will be higher capacitance or voltage rated, this is fine as long as it does not exceed 20% of the capacitance because then you may be taxing other components.

I would not pay $300 for 8 standard 10,000uF caps....
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Old 24th March 2005, 02:56 PM   #3
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As I recall, the PSU caps in the M 508 are known to have a hard time, and even blow up frequently due to the low working voltage of the original caps.....

As k-amps write: find some with a working voltage 20% over the supply
As I can see in the service manual, the M 508 has a rail of 74.5 Volt DC and 80V caps
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Old 24th March 2005, 03:33 PM   #4
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to make the answer less complicated: You can likely replace the capacitors with some 10,000uF 100V capacitors from any reputable manufacturer and be just fine. Shop distributors for price.
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Old 24th March 2005, 03:53 PM   #5
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Not as bad as some amps I fixed in the past (affectionally called Flame Linears by some of my fellow techs) in which the manufacturer assumed that cap voltage ratings were conservative and used higher rail voltages than cap V rating!! (if memory serves 75V caps and 80V PS)
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Old 24th March 2005, 04:34 PM   #6
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B Cullingford:
Is that the same "Linear" company that assumed that an output stage with max capacity of 250W easily could deliver an output of 200W for years after years
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Old 24th March 2005, 04:45 PM   #7
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that would be them - oh how I loved replacing PCB traces with wire!
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Old 24th March 2005, 05:09 PM   #8
K-amps is offline K-amps  United States
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And is that the same guy who rates his new toys as capable of driving 2400 watts into 1 ohm with BJT's that have less total dissipation than what they are driving at 1 ohm?
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Old 24th March 2005, 06:01 PM   #9
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It sounds very possible
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Old 24th March 2005, 08:00 PM   #10
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Just to be sure, the hard goo is not between the capacitors and the board is it?

Or is it actually leaking out of them?

because some manufactureres use glue for the large caps on the board.
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