Draytek Vigor 120 Annex A modem, Power supply question. 9v 500ma but I don't have the original one.

[#1]

I bought this Vigor 120 modem on Ebay, I know it's old but I just hope it will work.  It was cheap!  However I don't have a power supply, so will use a 9 volt one that I have in my 'old bits' box.  It gives more than the required current at 9 volts DC.  However, I don't know what the polarity should be. 

If anyone has a Draytek Vigor 120 Annex A modem, would you please be so kind as to let me know whether the centre pin in the modem and/or power connector is the Positive or negative terminal?  I know that most of these wall plug power supplies are positive centre pin, but not all.  I don't want to wreck my modem by plugging in a power supply with the wrong polarity.

Many thanks in advance.
Dave18

[#2]

In the absence of a response from someone who has one you could look inside and see whether the power socket connects using red and black wires, or to a component with an identifiable polarity - such as an electrolytic capacitor. Or there might be a clear earth rail on the circuit board that connects to shielding.

[#3]

Hi Davro,

thanks for the response, I had not thought of doing that to be honest.  Going to ask the local computer shop as the guy who owns it has been helpful in the past.  If he doesn't know, then I will have to do as you suggest.

Many thanks for taking the time to reply to my post.
Dave18

[#4]

@Dave18 I've just been out to the garage to look at my old modems (I now use 130s) for you and I can confirm that the centre pin on the PSU is positive.