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In Reply to: RE: SOS on Audio Research SP-9MKII posted by dd168168 on February 28, 2015 at 10:56:24
it is a problem with the muting circuitry. I had that issue with mine years ago. The culprit was a bad TI sourced NE555 timer.
Irritating, but that has been the only trouble I've had with mine in twenty years.
Follow Ups:
Thanks. How difficult is it to replace it? It seems a quite inexpesive part if that is the problem.
I had ARC perform the service so I can't tell you how easy the task was. I just remember the failed parts.
Not too difficult if you have decent soldering skills,and can get at it easily. Note there are two of those IC's in the timing circuit. Best thing is to replace them both.
Dan Santoni
Thanks. Which brand shoul I get?
The 555 timer is pretty generic. TI and Fairchild are probably the most popular.
Dan Santoni
Thanks for the quick anwsers. I have not opened the cover yet. But from the pictures online, it seems that NE555 was installed on the socket. It might be a lot easier job, just take the old ones out and insert the new ones.
Edits: 02/28/15
I've seen them with and without sockets. If you have the sockets then it's a five minute job. Make sure you orientate the IC the right way.
One other thing to look at if the IC's still don't work is C24. It is a 33ufd 16V capacitor. If that's failed the timer will think it's muted. The value controls the time it takes to un-mute.
Dan Santoni
Given the age it might be prudent to replace it if it is an electrolytic.
Dave
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