The woofers won't be damaged even if there was a crossover problem.
Its not uncommon to find a large value cap (100uf or more) 'across' the woofer in some form or another, typically there could be a series chain of two inductors feeding the woofer and with a cap and series resistor connected to the junction of the two inductors.
For fault-finding the electronics, the first thing to confirm is that all the power rails are correct. That includes any locally derived supplies scattered throughout the equipment.
Lightning damaged clock radios 😉 would tend towards a simple power supply failure that possible burns out any internal thermal fuse embedded in the transformer windings.
You might get lucky... just approach the fault finding logically and concentrate on finding out why any single specific feature etc doesn't work.
Its not uncommon to find a large value cap (100uf or more) 'across' the woofer in some form or another, typically there could be a series chain of two inductors feeding the woofer and with a cap and series resistor connected to the junction of the two inductors.
For fault-finding the electronics, the first thing to confirm is that all the power rails are correct. That includes any locally derived supplies scattered throughout the equipment.
Lightning damaged clock radios 😉 would tend towards a simple power supply failure that possible burns out any internal thermal fuse embedded in the transformer windings.
You might get lucky... just approach the fault finding logically and concentrate on finding out why any single specific feature etc doesn't work.
It was mentioned a couple of times about testing the amp outputs for DC. Do I test each speaker output on its own, in the obvious manner (red lead to +, black lead to -), or is it more complex (red lead to left +, black lead to right -, etc)? Do I need to send a signal through the amp, or can I run it deadhead? What DC range should I run on the meter?
The polarity of the meter does not matter. You should have near zero volts DC, so it doesn't matter if your read -5 or +5. Both are bad! 🙂
Typically I think under 0.1 VDC is what you want to see. Better is under 0.050
Best,
Erik
Typically I think under 0.1 VDC is what you want to see. Better is under 0.050
Best,
Erik
Thanks very much for the info, both Erik and Mooly. You have no idea how much I appreciate your help.
If the capacitors are properly rated, the amp shouldn't be able to hurt them even if it is broken as has been suggested.
When you said the woofers wouldn't budge, were you pressing them with your hand? You can check them for resistance.
You can damage your meter measuring a capacitor for resistance if it has a charge on it.
If they measure open circuit you have a problem. If they read the normal fraction of an ohm you should hear sound.
It is possible that inductors overheat and the insulation melts. This can be almost impossible to realise from a resistance measurement, but it is often accompanied by obvious discolouration and smell. If a turn has shorted they should be replaced.
Lightning strikes are measured in kilovolts or megavolts, so easy to rip through a cap. however exactly what failed is the question.
The caps are part of the frequency determining network and ultimately are vital to it working properly (for you to get the correct frequency response).
You've already got the speakers disassembled. The cap cost is like, 1/10th the cost of your labor. 🙂 Chuck the old one's and get some better sounding one's say I. It's like replacing the timing belt at 100,000 miles. Might as well do the water pump too. 🙂
Erik
Erik
Oh I wasn't going to use the damaged amp to test the speakers. I have an AVR sitting here not doing anything that would work fine as a test source.
Yep, I pressed both with my hand. I finally got one to break free with a nice snapping noise. It makes a crunchy sound when I push it back and forth now. One of the reputable online speaker repair shops told me they can now rebuild these woofers, but I don't know if they'll be able to get them like new. I doubt it. I'll keep them around anyway, just in case I decide to try the repair some day.
I guess my choice of words could have been better. Part of the diagnostic process is determining what may have caused the problem, what it might have caused to happen, and what collateral damage there may have been. This helps to make certain judgements. Anyway...
I ordered the caps from Parts Connexion. I'm really looking forward towards getting these done.
Next up: repair the veneer. Sitting in storage, the ebony veneer shrank, believe it or not. I'm thinking about doing a rosewood or walnut, whatever it was that B&W offered back then.
Next up: repair the veneer. Sitting in storage, the ebony veneer shrank, believe it or not. I'm thinking about doing a rosewood or walnut, whatever it was that B&W offered back then.
The MKP parts you recommended. I bought matched pairs of 6.8u and 10u caps in the 250V rating. For less than $30 shipped I'll have an all new high pass on the crossover.
I finished the B&W project today. All new caps in the crossovers, new 7 inch kevlar mid woofers. I brought them up on a 7.1 Sony AVR in 2 channel mode, using a Sony BDP as a source, with my trusty copy of Alan Parson's Sound Check II as the media. Even with this wallflower of an amp they sounded pretty good. Mostly.
I noticed a sizzling coming from the woofer on the right channel. Vocals and midrange at large were totally unaffected. The sizzling was very apparent during low bass tests (sub 100hz). I switched to the AVRs 'B' channels and the sizzle was still there. I flipped each speaker to its opposite side and the sizzle followed the speaker I first noticed it on.
So.. what is this now? I would think it has to be either the coil or the woofer itself. Since the driver is new, I'm leaning towards the coil. How can I test either to see the source of the problem? Should I switch the drivers in the cabinets and see if the sizzle moves with it?
I noticed a sizzling coming from the woofer on the right channel. Vocals and midrange at large were totally unaffected. The sizzling was very apparent during low bass tests (sub 100hz). I switched to the AVRs 'B' channels and the sizzle was still there. I flipped each speaker to its opposite side and the sizzle followed the speaker I first noticed it on.
So.. what is this now? I would think it has to be either the coil or the woofer itself. Since the driver is new, I'm leaning towards the coil. How can I test either to see the source of the problem? Should I switch the drivers in the cabinets and see if the sizzle moves with it?
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