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Old 06-27-2009, 06:14 PM   #1 (permalink)
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Default Replacing SP-30N(US) Adapter for Ext speakers

I need to replace the power adapter for the external speakers--SP-30N(US)--that came with an eMachines T3990. I'm probably safe getting a 9VDC, 200 to 500mA rated transformer, but what the core of the connector...is it (+) or (-)?
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Old 06-27-2009, 07:35 PM   #2 (permalink)
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Default Re: Replacing SP-30N(US) Adapter for Ext speakers

Can always use a multimeter to find that out.
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Old 06-27-2009, 08:55 PM   #3 (permalink)
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Default Re: Replacing SP-30N(US) Adapter for Ext speakers

Thanks for the idea. I have a digital multi-tester but only know how to measure the output voltage and current on a working adapter; and as I mentioned, I don't have an adapter for these speakers. Are you saying there are contacts on the motherboard that I can use?

I contacted eMachines' (Gateway) live tech support and was told that the company does not have any info about the speakers's power adapter's specs. Wow!
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Old 06-27-2009, 09:55 PM   #4 (permalink)
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Default Re: Replacing SP-30N(US) Adapter for Ext speakers

Ah, oops, guess I misunderstood what you meant, sorry. Is there a tip polarity symbol on the speakers anywhere?
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Old 06-29-2009, 01:21 AM   #5 (permalink)
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Default Re: Replacing SP-30N(US) Adapter for Ext speakers

Unfortunately no info is stamped on the speakeres regarding the polarity. But apparently you were correct: I spoke with an electronics engineer and he told me to plug in a 1/8" stereo connector into the speaker jack (without cable attached), clamp or touch a ground source on the case with the common (black cable) probe, and then use the hot (red cable) probe to touch the part on the 1/8" plug that represents the tip with the plug. If you get a negative reading, the tip is negative.

Another method is to plug in an adapter with an output of 9-12 VDC (no higher than 24 VDC), about 200 mA for a pair of small speakers, and listen for 60 Hz hum. If no hum then the polarity of the adapter for the self-powered speakers is correct; otherwise reverse the wiring on the adapter plug.

He said you can't do any harm., and he has used the latter method for years to test phasing etc. I hope this info will help others who may face the same problem. Now all I need to do it get a battery for my multi-tester, which died in storage. Aaargh!
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Old 06-29-2009, 04:05 AM   #6 (permalink)
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Default Re: Replacing SP-30N(US) Adapter for Ext speakers

Glad you figured it out .
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