crossover repair - checking caps and finding replacements

Talon

Member
2014-08-01 11:54 pm
My B&W 600 series speakers were hit with a power surge. The woofer coils just outright melted solid. I already bought two replacements. I decided to check the crossovers prior to taking the new drivers out of the box, just in case. The problem is that I don't have a capacitance check meter, just a lowly analog sweep VOM that has served me well for years.
I understand that you can use these to check the caps for signs of life, and that there are three basic forms of movement:

1. No movement - dead cap
2. No resistance - shorted cap
3. low to high resistance gradual sweep - good cap

Of course, nothing is ever right in my world, so I have a 4th movement - high to low sweep. I'm assuming these need to be replaced.

So my question is two-fold:

1. Can I know for certain if the cap is bad with the equipment I have on hand?

2. If these are bad and assuming the manufacturer can't provide the parts, where can I find direct replacement capacitors?
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Couple of quick thoughts...

Do you know what killed the woofers ? If it was an amplifier failure (high DC offset) then its unlikely the speaker caps would be damaged. If it was something else :eek: (such as mains) then anything is possible.

You need to do basic checks on the caps with them out of circuit (one end unsoldered).

Depending on the value of the cap, you may not get much of a response on a meter.

Your 'high to low' sweep could suggest that you are reading across an inductive component rather than a cap. That would be very meter specific. Make sure they are caps you are checking.

Replacement caps should be available from several sources. You need to note the value and the working voltage which will be marked on the old ones. Caps in speakers are usually non polarised (bi-polar) types.
 

Talon

Member
2014-08-01 11:54 pm
It was a lightning strike that done it. I came home to find the tuner sweeping FM without stopping, the preamp dead, fuses blown in the amp, and the woofers unable to budge. Also took out a few other things in the homestead but that was the stuff I cared about.

I'm definitely going across the caps. The inductors are very obvious. Two of them, two caps, one resistor. (Your typical 2nd order, I guess, not that I'm any kind of expert.)
I didn't realize I would have to unsolder the caps, though. I thought I could just test across them like a resistor.

I appreciate the help. I'm just starting to learn all this.
 

eriksquires

Member
2013-05-10 4:11 pm
Well it's too late to talk about the benefits of series mode surge protection. :)

B&W uses Mundorf MKP which are good but relatively inexpensive line for the midrange caps and I'm not sure what for less. They run around $7-$8 each, give or take.

Sources in the us are Parts Connection which is in the middle of their 20% off sale. Madisound doesn't seem to karry the MKP line. My recommendation is just to replace them all. :)

A cheaper alternative for caps in the woofer section are Axon, Bennic or Dayton.
 

Talon

Member
2014-08-01 11:54 pm
The sad part was I had a pretty decent surge protector inline. I guess it was a serious hit. I've since gotten a much better unit. (Or at least I hope it is)

I really appreciate the Parts Connection link, and the info on the manufacturer, Erik.

From what I can see, the cap values are 6u8 and 10uF, which I presume mean 6.8 microfarad and 10 microfarad, polyester, 100v. Is there anything else I should know when placing the order?
 

Talon

Member
2014-08-01 11:54 pm
B&W uses Mundorf MKP which are good but relatively inexpensive line for the midrange caps and I'm not sure what for less.

I just took a look at the page you linked, and those MKP are polypropylene caps, not the polyesters in my crossovers, which according to Parts Connection are MKT designation. Also, my caps are monolithic, not barrel type. Thats a lot of differences. Are these all going to be equivalent?
 

eriksquires

Member
2013-05-10 4:11 pm
The sad part was I had a pretty decent surge protector inline. I guess it was a serious hit. I've since gotten a much better unit. (Or at least I hope it is)

I really appreciate the Parts Connection link, and the info on the manufacturer, Erik.

From what I can see, the cap values are 6u8 and 10uF, which I presume mean 6.8 microfarad and 10 microfarad, polyester, 100v. Is there anything else I should know when placing the order?

Sounds about right.

Of course, 100V is the minimum voltage. If you can't find those you can always go upwards in voltage, but for more $$$. That is, if you can't find 6.8uF at 100V, you can buy 400V versions, which would be overkill. :)

Avoid any surge protector rated in "joule's." They are all too slow. :) Furman and others license series mode surge protection, which on top of being the best surge protection for AC, also limits line noise from around 3 kHz. If you want to talk more about that message me privately so we don't go too off topic. :)

Best,


Erik
 

ticknpop

Member
Paid Member
2005-05-28 9:43 pm
toronto
Don't hook up anything until you check your amp for DC output on each channel.
Sounds lik it's possibly what damaged the woofers after the lightning damaged the amp.

Buy at Least Solen Polypropelene ( or better) their not really very expensive - they have resellers in the UK - forget buying polyester cap replacements
 

eriksquires

Member
2013-05-10 4:11 pm
I just took a look at the page you linked, and those MKP are polypropylene caps, not the polyesters in my crossovers, which according to Parts Connection are MKT designation. Also, my caps are monolithic, not barrel type. Thats a lot of differences. Are these all going to be equivalent?

From a general performance point of view, any film cap with the matching uF and at least 100V will work. The Mundorf MKP's are better. :) B&W actually in some cases makes the same speaker, but one is more expensive. The more expensive line has Mundorf MKP's in them.

Going up beyond that B&W starts to use Mundorf Supreme's, which are black and cylindrical, but not sure which exact type.

Ticknpop is right about making sure your amp isn't fried. It's actually much more likely that it fried first. Rebuilding your speakers and reconnecting would just cause you to do this again. :)

Personally I'm just not a fan of Solen's, but I hear good things about their latest high-end caps. I would stick with Mundorf's, it's what B&W uses and I think you'll be pleasantly surprised.

Best,


Erik
 
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Talon

Member
2014-08-01 11:54 pm
Don't hook up anything until you check your amp for DC output on each channel.
Sounds lik it's possibly what damaged the woofers after the lightning damaged the amp.

I'm going to test the speakers on an unused AVR I have sitting around. The original amp is going to get tested. The fuses are blown, so I have to replace those. Hopefully nothing else is damaged. Its an old Adcom, which has a lot of sentimental value to me.

Buy at Least Solen Polypropelene ( or better) their not really very expensive - they have resellers in the UK - forget buying polyester cap replacements

I'm budgeting about $10 each for caps, so it looks like I'll have a wide variety of choices. I'll post up my choices here and see what the community says.
 

Talon

Member
2014-08-01 11:54 pm
From a general performance point of view, any film cap with the matching uF and at least 100V will work. The Mundorf MKP's are better. :) B&W actually in some cases makes the same speaker, but one is more expensive. The more expensive line has Mundorf MKP's in them ... I would stick with Mundorf's, it's what B&W uses and I think you'll be pleasantly surprised.


Good advice. Thank you Erik.:cheers:
 

ticknpop

Member
Paid Member
2005-05-28 9:43 pm
toronto
Unfortunately i'd put money on the amp being fried - blown output stage at least.
Yes Solen aren't my favorite cap either , but what I like costs too much to be sensible for this repair , besides you'll need money for the amp parts - I'd like to be wrong this time, but...............

I wouldn't worry about cap shapes , just stick them with silicon sealant if you can't get cable ties to hold them
 
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One more thing... my B&W crossovers have rectangular potted caps, but all the caps I've found to replace them are barrel type. Are there any Mundorf's or whatever available in the rectangular single ended version?

All the mundorks are superior to the polyester caps you are replacing. Mundorf briefly made a line of rectangular potted caps in black plastic but have been discontinued in favor of the Evo variants.

Performance wise, potting vs. cigar shaped makess no difference except to auto insertion machines
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
It was a lightning strike that done it. I came home to find the tuner sweeping FM without stopping, the preamp dead, fuses blown in the amp, and the woofers unable to budge. Also took out a few other things in the homestead but that was the stuff I cared about.

I've seen this scenario many many times as a repair tech. All bets are off when it comes to trying to be logical as to what may or may not have failed. It sounds like the strike got into the mains from somewhere close by rather than a direct hit.

I think you've a pretty good chance (not guaranteed but pretty good) that the speaker crossover parts will be OK and that the woofer failure is down to a failed amp putting the supply voltage across them.

The electronic problems (tuner/amp etc) are almost certainly going to be non-logical to fault find on. I've seen power supply front ends blown to pieces and yet replacing the obvious damaged part (say a bridge) restores normal operation. Other have no obvious damage and yet its a catalogue of one problem after another, totally random failed parts.

Hope you get it all sorted :)
 

Talon

Member
2014-08-01 11:54 pm
To expand on what Mooly said.. The woofer coils are probably disfigured in the gap. It is probably the capacitors that saved the tweeters. If you can now confirm that the amp has no appreciable DC at the output. If it does (and maybe even if not) the caps might be OK.

I'm trying to understand this.. I can check the amp output and if I don't see any DC at the outputs that means I may not need caps in the crossovers? That would be good news. I'm only looking at about $9 per speaker but it would be nice if I could avoid maiming those boards.

I'm pretty sure the tweeters are fine in any case. After the damage, I hooked the speakers up to an integrated amp and heard very clear sound coming out of them, at a low volume though. I checked them yesterday with the VOM and saw around 3 ohms resistance, if I recall, and touching the leads to the tweeter harness produced a crackle.
 
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Talon

Member
2014-08-01 11:54 pm
I think you've a pretty good chance (not guaranteed but pretty good) that the speaker crossover parts will be OK and that the woofer failure is down to a failed amp putting the supply voltage across them.

I guess I could just put the new woofers in and see if everything works. I imagine there's nothing the crossover can do to the woofers even if the caps are damaged, right? I mean, the caps don't touch the woofer side of the circuit, they're in series with the tweeter.

Which brings to mind - what about the inductors? Is there anything beyond a simple continuity check that I should be concerned about? These are a pair of rather nice looking air cores which according to the B&W TM are 1.1mH and 0.08mH.

The electronic problems (tuner/amp etc) are almost certainly going to be non-logical to fault find on. I've seen power supply front ends blown to pieces and yet replacing the obvious damaged part (say a bridge) restores normal operation. Other have no obvious damage and yet its a catalogue of one problem after another, totally random failed parts.

Hope you get it all sorted :)

Thanks for the advice and wishes. :cheers:

Sounds to me like I should get a capacitor checker or maybe splurge on a full featured digital meter and get to work on that stuff. The preamp and tuner are vintage Hafler and there is almost no technical info on them to be found anywhere, though, so I will have a steep learning curve on this. I already ordered a bunch of replacement logic parts but I hadn't really thought much about the non-logic. Maybe I should try to fix a broken clock radio or something before getting in to the higher end stuff...