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Frank D
04-02-2009, 01:12 PM
Hello everyone. This may have been covered before so if it has please excuse me. I have a pair of L100's that I purchased new in 1975. One speaker is only driving the woofer, no sound from the midrange or tweeter. Is this a problem that someone has encountered before and what would be the fix? Thanks.

ratitifb
04-02-2009, 01:33 PM
Lpad and/or X-over checking ;)

duaneage
04-03-2009, 07:39 AM
Carefully remove the mid and tweeter and using a 1.5 volt battery you can verify if they respond to voltage or not. If you hear a click from each one the problem is either the adjusters on the front or the capacitors that crossover the signal to the drivers. I would consider getting some contact cleaner spray from radio shack and treating the adjusters to a bath first.

It is not uncommon for the mid and tweeter to be blown, they were not really crossed over very well with single capacitors and judicious use of the volume control has killed many over the years. You can get replacement L pad controls from partsexpress.com and new drivers from ebay. Sometimes they are offered here in Marketplace as well.

Fred Sanford
04-03-2009, 09:00 AM
Carefully remove the mid and tweeter and using a 1.5 volt battery you can verify if they respond to voltage or not. If you hear a click from each one the problem is either the adjusters on the front or the capacitors that crossover the signal to the drivers. I would consider getting some contact cleaner spray from radio shack and treating the adjusters to a bath first.

It is not uncommon for the mid and tweeter to be blown, they were not really crossed over very well with single capacitors and judicious use of the volume control has killed many over the years. You can get replacement L pad controls from partsexpress.com and new drivers from ebay. Sometimes they are offered here in Marketplace as well.

I wouldn't ever recommend testing a tweeter directly from a battery. Maybe test it from another (known good) crossover network's tweeter leads.

je

jaynemo
04-03-2009, 09:12 AM
Just my humble opinion, never use contact spray cleaner unless you can verify the modern solvents used in it will not harm vintage sliders, pots or L-pads.

Maybe not so much mechanical L-pads, but cheep contact cleaner can destroy 30 year old plastics and carbon based switches. A great remedy for L-pads is good old ethanol alcohol, with adequate purity levels found in most liquor stores under the name of "Graves Grain" alcohol. However, some or most L-pads are sealed. So they need to be soaked. Hard doing with a spray can. Cheep too, about $4.00 a 1/2 pint. Make your self a cocktail on whats left over. I rebuilt a set of crossovers on my verticle arrays and used all new parts, I have spare L-pads left over if they are your last resort. I used Madisound for my new L-pads, they barely sqeek in with the real estate on the X-over boards. I also have the X-over schematic if you need it. PM me.

robertbartsch
04-03-2009, 10:01 AM
....you could also take an Ohm reading on the mid and tweeter drivers to tell you if the voice coils have been burned out, I suppose.

...I thought the juice from a 1.5 volt battery was DC and very harmful to mid and tweeter voice coils...

ROSSO
04-03-2009, 10:34 AM
Hello everyone. This may have been covered before so if it has please excuse me. I have a pair of L100's that I purchased new in 1975. One speaker is only driving the woofer, no sound from the midrange or tweeter. Is this a problem that someone has encountered before and what would be the fix? Thanks.Swap the mids and tweets between the two cabinets and see if the problem follows. If the problem stays with one cabinet, then its likely the crossover or perhaps the L-pads. Because two of the mounting screws are obscured by the JBL foilcal with the serial number stamped on it, it's a major pain to remove the crossover. Very tricky to remove the foilcal without damaging it. If you are very careful, heat from a blow dryer or a heat gun will soften the adhesive enough so that the foil can be vary carefully lifted with a thin, flexible, wide-blade putty knife. Once they are kinked its almost impossible to make them flat again. Too much heat will obviously strip the paint from the front baffle. Once they are out you might as well replace the capacitors, they are cheap.

duaneage
04-03-2009, 12:34 PM
....you could also take an Ohm reading on the mid and tweeter drivers to tell you if the voice coils have been burned out, I suppose.

...I thought the juice from a 1.5 volt battery was DC and very harmful to mid and tweeter voice coils...


Touching a 1.5 volt battery to a mid or a tweeter is not going to damage them. Especially the mid.
9 volts or 12 would be too much.
You're not powering them for any length of time, just looking for a pulse.

Meters work too, he did not indicate that he had any test equipment. But everyone has a battery somewhere/

duaneage
04-03-2009, 12:36 PM
Just my humble opinion, never use contact spray cleaner unless you can verify the modern solvents used in it will not harm vintage sliders, pots or L-pads.

Maybe not so much mechanical L-pads, but cheep contact cleaner can destroy 30 year old plastics and carbon based switches. A great remedy for L-pads is good old ethanol alcohol, with adequate purity levels found in most liquor stores under the name of "Graves Grain" alcohol. However, some or most L-pads are sealed. So they need to be soaked. Hard doing with a spray can. Cheep too, about $4.00 a 1/2 pint. Make your self a cocktail on whats left over. I rebuilt a set of crossovers on my verticle arrays and used all new parts, I have spare L-pads left over if they are your last resort. I used Madisound for my new L-pads, they barely sqeek in with the real estate on the X-over boards. I also have the X-over schematic if you need it. PM me.


The controls used in the L100 clean up just fine with contact cleaner spray. I would replace them since they are so old and cleaning just delays their eventual demise. For about 20 bucks you can get brand spanking new ones from partsexpress that match just dandy.

Fred Sanford
04-03-2009, 05:12 PM
Touching a 1.5 volt battery to a mid or a tweeter is not going to damage them. Especially the mid.
9 volts or 12 would be too much.
You're not powering them for any length of time, just looking for a pulse.

Meters work too, he did not indicate that he had any test equipment. But everyone has a battery somewhere/

I chose my words carefully:

"I wouldn't ever recommend testing a tweeter directly from a battery."

Partly because I think it's an unnecessary risk, and partly because I've seen many people hold a battery to the speaker leads for a long time, even when they've been told specifically to just "touch" them.

If I care about the tweeter, I don't run signal to it without an appropriate filter in line. If I care about the tweeter, I don't apply DC to it.

Actually, I've never done it at all, even if I didn't care about the tweeter.

je

Mr. Widget
04-03-2009, 11:32 PM
"I wouldn't ever recommend testing a tweeter directly from a battery."Just think of the LE25 as a Bose woofer. :applaud:


Widget

Frank D
04-08-2009, 05:21 PM
I sprayed down the contacts with contact cleaner and got the midrange to work. I will give them another spray when I get somemore contact cleaner and some more time.

Frank D
04-11-2009, 10:57 AM
My L100's could probably use new crossovers but replacing them is beyond my scope of expertise. Does anybody know of and shops in the Hudson Valley region of NY that can do that work?

Mr. Widget
04-11-2009, 03:45 PM
Have you ever used a soldering iron? How about a wire nut? The crossover is simply two caps and two L-pads... it would be difficult to screw up... then again, I doubt you need to mess with them anyway.


Widget

Frank D
04-11-2009, 06:23 PM
I could handle the wire nuts but with the soldering iron, I could turn them into useless piles of burned junk. Also how would I go about removing them and are there new replacement crossovers of any kind available, not just used originals?