Help with dunlavy SM1 crossover

[ebenai]

I got a pair of these speakers but one isn't working. No output from the woofers. I connected the woofers directly to the amp and they appear to be working fine. I think the problem is the crossover (the tweteer does work fine). The circuit board and all the components look fine (external inspection). I would like to know where could I send it to be checked and repaired. I'm not up to the task and don't want to ruin it.

[R-Carpenter]

Should be a simple 2 way crossover in there. If you post the picture, we would probably guide you through step by step. All you need is a DMM and soldering iron.

[ebenai]

Thanks for you prompt response.

Here are a couple of pictures.

Thanks

[bear]

there ought to be DC resistance between the woofer and the input terminals... check what the "good" speaker reads for DCR, then compare to the bad one. IF the bad one is infinite, or very very high, you probably have a broken connection, find it and resolder. You can merely trace from the input along the path, and also from the output side back to the input...

the way to check that is with the DVM measuring resistance connected to the two speaker input posts (from the amp, no amp connected)

For tracing the circuit path, that's the " + " input terminal to the " + " woofer terminal... the other terminal/post is nominally ground, and should measure 0 from any "ground" or " - " terminal to another...

IF you get something like 1 or 2 ohms (in that range) when you measure from the input + to the woofer +, on the good one, and open on the bad one, you probably have a bad series resistor...

It's pretty simple in that respect... you can likely find it by inspection and tracing the path for continuity - the coils are moderately low DCR, like an ohm or less... FYI

_-_-bear

[R-Carpenter]

Wow, nice crossover. Nice parts.
Anyway, what Bear said plus I'll try to make it simpler.
Get a DMM such as
http://www.parts-express.com/pe/show...number=390-730
Rat Shack has even a cheaper one, I think for $9 probably in Christmas packaging.
Start with the simple things.
Check the wires running from the woofer to the crossover. See if there's any internal brakes.
Inspect the crossover itself under a good lite and see if PCB board is cracked anywhere.
Look at Inductors, capacitors and resistors and see if the leads came loose.
If nothing showing, pull out that Christmasy Multimeter.

The idea is very basic. A blown component will have either very high or infinite resistance.
You can also make a drawing and mark measured components on it so there's no mix up.
Just for the hell of it, you could pull out the crossover from the working speaker and compare the values as you go through.
My personal suspicion is that on this crossover it may be one of the sand cast resistors under the coil.
I have seen setups like this overheat.
Let us know of the progress.

[ebenai]

The resistance between the inputs of the woofers is out of the range and cannot be measured. In contrast in good speaker there is a small resistance (measurable). The problem is that all the connections, cables, etc look just fine and I cannot detect where the problem is. I noticed that bear has an electronics store and does repairs. Would you be interested in looking at it?
Thanks

Elie

[R-Carpenter]

If the resistance between (+) and (-) of the woofer is infinite then the voice coil of the woofer is on the way out and the woofer has to be replaced. The woofer should have somewhere around 6 ohm DC resistance.

[ebenai]

I'm embarrased to say that I tested the crossover without connecting the woofers. Let me try again.

[bear]

Originally posted by ebenai
The resistance between the inputs of the woofers is out of the range and cannot be measured. In contrast in good speaker there is a small resistance (measurable). The problem is that all the connections, cables, etc look just fine and I cannot detect where the problem is. I noticed that bear has an electronics store and does repairs. Would you be interested in looking at it?
Thanks

Elie

well we can simplify even more...

if you have the woofer inputs available, without the xover connected to it, you can just attach the woofer to the output of your amplifier (don't short the wires!), if the woofer is ok then it will play (not so good sounding) as a "full range speaker". If it has no output, it is open.

IF it is open, you can visually inspect the lead in wires from each terminal on the woofer basket - they are braided and sometimes will show a crack or open. If that has happened any relatively local speaker recone shop can repair (look for pro sound dealers).

IF the woofer is open, ur in a bit of a bind. You'll need to accurately have the remaining woofer tested for T/S parameters, and also frequency response, then find a suitable replacement that has the same basket size. Then install, ur done.

I am sorry that I can't look at the xover for you... that would cost you more than it is worth. imho. First check the woofer as I described, then you will know if the problem is in the woofer itself or in the xover. It is vaguely possible that there is a problem in both, but certainly, if the woofer is blown, that is where to start.

_-_-bear

PS. you can use a random "cheap" woofer for testing the xover's performance... you can also compare the "good" side to the "bad" and see if they sound the same... be sure to mark them clearly so they don't get confused...

[ebenai]

Thanks for all your help. I've already tested the woofers by connecting them directly to the amp and the work well. If I do it through the crossover I get some ouptut but at very low volume.

Thanks again