On 5/23/14, 3:34 PM, Robert Green wrote:
"David Martel" wrote in message
...


Since I have so many I'll probably have to just pick a model and go from
there. The Technics with the 15" woofer seems to woof OK but the tweeter
and midrange seem inert. I have not yet jacked them out of their case yet
because it's in an awkward place and because I just noticed the problem the
other day. I think I need to round up all the ones worth saving to try to
figure out what's what.

Now what sort of tools do you have? A multimeter? An oscilloscope? A
soldering iron?

All of the above but the scope's a pretty cheesy penscope not good for much.
I want to be able to check the crossover networks and haven't come across
much help in that area on the web. I have a DVM that has a capacitance
checker built-in, but I recall from previous threads about the flood of bad
caps a few years back, that the DVM can't really check out all the possible
flaws in a bad cap.

I've had capacitance checkers in the past, but they went bad. A
crossover capacitor may be beyond the range of a checker, anyway.

Big ones can be checked by the time constant using a couple of DMMs and
a calculator. (I used three DMMs, two to determine the voltage and
resistance of the third, on it's highest resistance range.) I found out
that bad nonpolar electrolytics give whacky results.

As I recall, the other thing to check is the capacitor's resistance.
I'd skip that.

Ok let's hook the speaker up to a good audio signal. Turn the volume
down
and the power on. Now bring the volume up. Hear anything?

I know the basics. I just need to find out more about crossover network
troubleshooting and how to determine what kind of replacements I should use
for speakers/tweeters/woofers that don't have and characteristics marked on
them. I'm busy reading up on the design of cross-over network so I can
better understand their function in the world of the Dead Speakers.

It's usually electrolytic capacitors, not coils or resistors, that go
bad. I have a Radio Shack DMM from 1979. I pull it off the shelf when
I need to check audio voltages up to 20kHz; most won't do that. A scope
can also show you where you're losing the signal, but if one side of the
audio circuit is grounded, you have to be careful where you clip the
ground lead.

I didn't bother to check with signals. Checking a few capacitors with
time constants made a believer of me; so I replaced them all. I needed
a chisel to get the circuit boards unglued from the cabinets and to get
the capacitors unglued from the boards. Their values were marked.