250Ti BQ LTD crossover issue

[Dagfinn]

So, I recently aquired a set of 250Ti BQ LTD in very nice condition. Except for the left tweeter not playing 100% silent. I switched the tweeters, and the driver is fine, it plays in the right speaker box. So, my problem must be in the tweeter section of crossover. I've opened it to take a look, but how to proceed? Attached is a pic of the crossover, any suggestions? Any help very much appreciated... (I have a LCR meter and regular v-meter). Regards, Dagfinn

[rdgrimes]

To rule out a wiring issue run a pair of jumpers directly from the board to a tweeter to see if it works. Make sure nothing is mis-wired on that board, they are all color coded.

[Dagfinn]

All checks out, colour coding is correct. Monster cable soldered to the board, I get a weak signal from the tweeter when measuring some resistors, so cabling from board to tweeter is good. Nothing feels loose to the touch. I haven't quite managed to connect schematic to the circuit, hard to see other side...

[Don C]

I'd be disconnecting everything else for a minute to check the switch with an ohmmeter.

[Robh3606]

I'd be disconnecting everything else for a minute to check the switch with an ohmmeter.

The switch won't kill the tweeter. It just switches out attenuation and is floating when +2 engaged. R17 should not have a solder ball on top. Could be a broken lead under there. You can take out R18 and the switched components you still have a functioning tweeter. You can't take out R17 without taking out the tweeter.

Take a close look at both leads there is no stress relief on them and they could have fractured.

Rob :)

[grumpy]

May just look like a solder ball on R17... the groove in the resistor 'case' just amplifies this perspective.

At any rate, if the wiring to HF is good and the other drivers play, there's an open (signal path in series, such as the caps) or a short (to ground, probably after the caps) in just a few related parts (including solder joints).

If a soldering iron and associated skills are available, this should be straightforward to address (pull one leg of a suspect part that's going to ground, or bypass/jumper a series connection... and use very low volume noise as a source and perhaps insert a capacitor in-line, say 1-10uF, for more tweeter-safety).

An oscilloscope (even a very cheap USB based thing) would be nice and quick, but not everyone has such a thing handy, and there is a learning curve.

Nice speakers, and worth some effort to repair/resolve.

[Dagfinn]

Thanks, guys. I'll check closer when I get it out, but I think I'll have to get help, getting to the small caps underneath will be a bit over my comfort level as far as soldering. But I'll try to find the fault, at least. Here is the working one, in non-standard position, perhaps. One owner, very nice and shiny still :). Can't wait to get them playing properly!

[Dagfinn]

So, while the c.o. is out for repairs, I'm toying with the thought of going fully 4-way active. Use a dbx 234Xs, as I already have one in house. Do one speaker first, see if I can match up it up to the passive. There's probably some issue with this I'm not aware of yet? Advice appreciated :). Dagfinn