Humming Speaker Protection relay when powering up (newbie question) - diyAudio
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Old 23rd October 2007, 10:10 PM   #1
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Post Humming Speaker Protection relay when powering up (newbie question)

Hi,
I'm working on a restoration Pioneer SA-9800.
The machine was a DOA when I got it. I now have it playing, but I have a annoying problem.
All the voltages on the scematic are present. And the protection relay for the speakers comes in.... VERY SLOWLY. It starts with a soft humm, becomes a rattle, and than the machine plays. When it hase done this, next time it powers up afterwards it clicks on reasonably 'normal'.
leave it for 20 minutes and its the humming sound again. I think it might be a slowcharging condenser or something.
Mains are 230 Volts AC, when I test it its mostly at 226, and I have the machine set at 220VAC.
The relay is a 48 volts.

I'm an newbie at this, I tried wising up by rereading everthing I have om electronics books, but this one stumps me.

Is there anyone out there who can give me a heads-up? And point me in the right direction?

thank
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Old 24th October 2007, 01:37 AM   #2
Leolabs is offline Leolabs  Malaysia
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Sounds like a power amp problem???
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Old 24th October 2007, 05:53 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
can you decypher the circuit driving the relay?
and post the schematic?
It might be just half a dozen components.
Is the relay AC or DC type?
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regards Andrew T.
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Old 21st November 2007, 10:20 AM   #4
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Default problem found!

As per the instructions from AndrewT i zooomed in on the cuircuit driving the relay.
All voltages were within spec (and that for a 30 year old amp). All seemd ok. the voltage went up correctly up to a zener diode controlling the last step in the cascade to tripping the transistor powering the coil.
But the zenerdiode did not trip correctly. I replaced the zener diode and the machine worked fine again.

So AndrewT thanks!
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Old 21st November 2007, 01:32 PM   #5
K-amps is offline K-amps  United States
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It is also a good idea to replace any caps that may have dried out. That can also cause chattering of relays.
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