Selling Damaged Magicos

I guess I know nothing about using the multimeter. I have a GDT-11 from GB Instruments that I've hardly ever used. I read the instructions online and set the dial to 200 ohms which is the lowest ohm setting. When I touched the binding posts with the probes, the read out stayed at 1.

Yes, it does seem very unlikely that physical mishandling could have caused this problem on both speakers. But it would also be unusual, although not unheard of, for an amp to put out large amounts of DC on both channels. And if perchance it was a tube amp, in most cases it would be nearly impossible because DC would be blocked by the output transformer most tube amps utilize. So before sending the woofers cross-country it would make sense to make the measurements I suggested, which may provide added confidence in the diagnosis that is being presumed, or might point in a different direction.

I found some information on your meter. The 200 ohm scale is the correct choice. As you probably realize, one test lead should be plugged into the black "com" jack, and the other into the red jack that is just above it (and not into the uppermost red jack). Also, look to see if "BAT" appears on the display, which would indicate that the battery should be replaced.

Then touch the two metal ends of the test leads together. The meter should indicate "000" signifying zero ohms on that scale, or perhaps "001" which signifies 1 ohm but would be within the meter’s expectable accuracy tolerance.

Then proceed as I indicated in my earlier post.  Be sure to disconnect the amp from the speakers when making the measurements, as I indicated.

Regards,
-- Al

Thanks Al. I'll give it a try.

The tester seems to be functioning correctly. When I touch the leads together, the reading fluctuates between -1 and <2. It stops at -1. When I touch the speaker terminals, it goes to 1 and stays there.

Very easy test, take a 9V battery, touch it to the terminals at the speaker, + to the red/positive terminal and - to the black/negative terminal, this should cause outward cone movement, if no movement the driver is blown.   In most cases of excessive power or DC to the voice coil the coil will delaminate or change shape slightly causing it to rub against the pole plate, it'll also have a slightly "burnt" smell caused by the lacquer melting because of heat.

To test for rub place three fingers around the circumference of the dustcap and push in gently, the cone should move freely.

Best of luck


Peter