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Old 9th March 2010, 04:37 PM   #1
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Default Need Help fixing Nikko Alpha 230

Hello, new to this forum but impressed with the knowledgeable posts I've read.

So, my beloved 27-year-old Nikko Alpha 230 finally quit, after 20 years of road use!

It will repeatedly go in and out of protection mode- works for 20-30 seconds, goes into protect, comes out after several seconds and works again, then goes into protect again...

There have been some other symptoms over the last 6 months leading up to this failure... perhaps they are related and might lend clues:

1) When I'd first start the amp, one channel would not have output, though both meters would read equal power out. Raising the volume up for a split second would cause the out channel to kick in and it would usually work for the rest of the night.

2) On rare occasions, I would lose one channel during a gig but the meters would still show both channels good, and giving the amp a slight tap (a gentle whack) would cause it to work again.

3) Sometimes there would be audible high-frequency distortion in one channel.

But for the most part it would work, then suddenly started going into protect mode.

FYI, there is a decent amount of superficial corrosion throughout the amp-it has been extensively roaded for two decades and stored in a hot humid garage. Not sure if this might be a factor in where to look for the problem.

Also, It had been serviced once during its lifetime-in 1995 I loaned it out and it was returned fried, service center replaced the output transistors on one channel. No problems since until now.

I love this amp and want to get it working again. I have basic electronics skills and knowledge, but I am not a very experienced at component-level troubleshooting. Most of my test equipment I sold a long time ago, and currently I only have a DMM and a sweep tone generator.

I'd greatly appreciate schematics and suggestions as to how and where to find the problem.

Thanks much!
-Jason
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Old 9th March 2010, 08:41 PM   #2
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If it comes on with a whack then its likely to have a dry joint or a loose connection somewere. Inspect it thoroughly and go over any dodgy looking solder joints.
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Old 9th March 2010, 09:37 PM   #3
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Hi,
Thanks for your reply.
Since the amp began going into protection mode (last Friday) it no longer comes on with a whack.
Goes in an out of Protect mode several times per song.
No problem with speakers or cabling.
Any other ideas?
Thanks.
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Old 19th November 2010, 04:32 PM   #4
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Default Schematics

Brian Donegan of twisted pear audio sent me the schematics. I have attached them. It seems the leading issue seems to be the driver amps. If you take the bottom cover off (8 outer screws), and use a meter to check for shorts on the main transistors on the heatsinks in the middle you will probably find several of them shorted, they are the 2SA1095 and 2SC2565's, you may want to look at the preamp as well, as it can rail the drivers and take it all down.
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File Type: jpg NikkoAlpha230-PS.jpg (206.8 KB, 123 views)
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