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how to determine tip polarity of device

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I have a mini cassette recorder that will take 3V DC input from AC adapter. My generic adapter can do either negative or positive tip polarity. The manual for the recorder doesn't specify polarity; nor does the recorder itself. So how can I determine whether I should make my adapter positive or negative tip polarity? Thanks.
 

If there's a battery compartment, you could do a resistance measurement between the DC connector's contacts, and the most positive / most negative contacts in the battery compartment. Results usually make it clear what is + and - for the DC connector.

Otherwise, if manual doesn't say, AND you don't have original DC adapter that comes with the recorder, AND recorder itself has no relevant markings, AND there's no battery compartment (you unlucky f... :x ), only way would be to open up the recorder & check out the circuit inside.

(or just gamble but risk damaging the recorder - tip positive is the most common arrangement but there are many exceptions)

What brand & model cassette recorder are we talking about here?
 

Are you sure it isn't embossed on the casing? It is not always easy to see. Otherwise the make and model number of the device and/or adaptor may yield further information.

Keith
 

RetroTechie said:
If there's a battery compartment, you could do a resistance measurement between the DC connector's contacts, and the most positive / most negative contacts in the battery compartment. Results usually make it clear what is + and - for the DC connector.

Otherwise, if manual doesn't say, AND you don't have original DC adapter that comes with the recorder, AND recorder itself has no relevant markings, AND there's no battery compartment (you unlucky f... :x ), only way would be to open up the recorder & check out the circuit inside.

(or just gamble but risk damaging the recorder - tip positive is the most common arrangement but there are many exceptions)

What brand & model cassette recorder are we talking about here?
Click to expand...

It's an old Lanier recorder, called the "Vest Pocket Secretary" which was advertised by Arnold Palmer when it was new. I didn't need yet another AC/DC adapter when I purchased the recorder. In fact, I just used batteries for a number of years. Now I want to use the wall plug and discovered that the manual doesn't have tip polarity info.

Both you and Keith mentioned info embossed on the casing, which I do know can be hard to see, but it just says "DV IN 3V." Nothing about tip polarity. And accessories listed in manual just says 3V.

I'm a biologist with too little experience to understand exactly how my ohmmeter will make the polarity clear. Can you maybe add a little explanation? Thanks.
 

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