Yamaha DSP A-990

Nov 06, 2006 3 Replies
S

I'm hoping that there may be somebody with a 5 channel amplifier Yamaha DSP A-990. I like my old machine, 6 years old, a fantastic sound and video processor. Happened to short the outputs and blew most of the 14 power darlington transistors. I have repaired with newer equivalents and all e-c-b voltages are OK, but 5 seconds after start, there is a safety relay that switches power off. I can't figure out why and what the sensors react on. Complicated electronics. Now I just wonder if someone happen to have such a machine and if there is also someone who have schematics. Yamaha don't not respond positively on my request, say they have no service on such a obsolete amplifier.



Thanks!



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P

"steve" wrote in news: snipped-for-privacy@b28g2000cwb.googlegroups.com:

Looks like the following site has free info on your unit:

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D

Usually looking for a DC offset to protect the speakers. Maybe also oscillation. A scope should tell all.

*Money isn't everything, but it sure keeps the kids in touch * Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound.
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M

Not finding this model number, at least not on the Yamaha's US tech site.

When the outputs blew, they probably took out one or more resistors, sometimes a 330 ohm or so which is between the emitters of the two driver transistors, or a series resistor going to the base of an output transistor, usually about 4.7 ohms, an emitter resistor, usually .22 ohms at 5 watts dual package, or, and this seems most likely to me, a resistor supplying B+ or - to the collector of a driver transistor. Usually in the one to ten ohm range.

Mark Z.

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