Yamaha DSP A-990

[steve]

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!

 

[propman]

DSP A-990

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

http://www.eserviceinfo.com/

 

[Dave Plowman (News)]

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.

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

 

[Mark D. Zacharias]

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!

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.