How to troubleshoot & repair this 3-way XO?

[cdwitmer]

I need to repair a nice pair of Pioneer 3-way speakers that cost the equivalent of US$2000 when they were built in 1986. At the time, these were the best consumer-use speakers Pioneer made (excluding the TAD line). I just reconed the woofers and all the transducers sound excellent, except there is intermittent noise coming from one cabinet that is almost certainly due to the crossover network. I am assuming it is the network because it persists 1) regardless of what amp I use, and 2) even after I swap the drivers between the two cabinets.

I have never had to troubleshoot and repair a passive crossover network before. This is a somewhat more complicated network than the ones I have made myself in the past, as this is a "Watkins woofer" (using dual voice coils to extend the bass).

What parts can go bad in a passive XO? I am guessing it must be the capacitors. Should I just replace all the caps? Some of them are quite large and probably expensive. Any advice on how to proceed would be appreciated. I don't have much in the way of testing and measuring equipment.

Thanks!

Christopher Witmer

[ThomasW]

As old as they are it's either the caps, or an intermittent in one of the inductors. (more likely it's a cap, they have a finite shelf life)

To test any of these they must be removed from the circuit, and individually checked. A digital multi-meter will test continuity, it takes a LCR meter to measure values of caps and inductors.

[cdwitmer]

Thanks for the advice, Thomas. Sorry for requesting long-distance diagnostics, but if the good people on this board would be so kind, please indulge me. (Just pretend you are a telepath from the former Soviet Union.) Does this symptom ring a bell? --

The problem is intermittent. When it occurs, it occurs early during use, and as time passes, it disappears. Rather than a lot of noise occuring, there tends to be a loss of sound from the loudspeaker. For example, this morning I decided to test the problem and played only the offending loudspeaker. At first, no sound would come out at all. Then, I got sound -- without any distortion that I could notice -- for about three minutes. At that point, I lost sound momentarily. I could hear the sound rapidly fading out and disappearing. Then it came back and I could listen for the next 90 minutes straight without a single glitch. This is a very typical pattern. If problems occur, they occur early in use and then disappear: almost as if "warming up" solves the problem. Does this suggest anything? This loudspeaker has a rate efficiency of 90dB, and I never play loud, so I think at most I am putting a watt or two into these speakers most of the time. I wonder if that is enough to cause a thermal “warming up” effect. (It is interesting that this problem was not occurring at all during the warm summer months, but started only recently, so temperature differences may be involved.) At any rate, if anyone can offer insights, I'd be grateful. I think it is likely to be a pain in the neck to detach the crossover from the cabinet to work on it, and I need all the support I can get . . . THANKS!

Christopher Witmer

[ThomasW]

Sorry, but ...............

You must remove the crossover and take it apart to diagnose the problem.

[Kevin P]

Is the entire speaker cutting out, or just one of the drivers?

If it's the entire speaker, I would venture it's a bad solder joint, either on the crossover board or on the back of the binding posts. Resoldering might just do the trick.

If it's just one of the drivers, it could still be a solder joint on the crossover board, or a failing component. If it's just one of the drivers, which one is it?

[JonMarsh]

Another possibility might be a protective device, such as a PTC resistor or fuse-istor. But I agree that I'd look for solder joint issues first. If it was a single component in one of the filter sections, just that driver would be cutting out.

~Jon

[cdwitmer]

Thanks for the replies. All three units are affected simultaneously, so I think I had better check solder joints and connections first. If that doesn't do it, I'll probably wimp out and have Pioneer look at it, unless they quote me some outrageous figure that makes me want to just rebuild the crossovers instead.

[cdwitmer]

I just wanted to say thanks for the suggestions on the intermittent problems I was having with my Pioneer loudspeakers. Apparently, the passive crossover components are all still in fine shape. The problem was a loose connection on the inside of the speaker terminals, and rectifying it was a simple matter of tightening a nut. I also cleaned the terminals. Sounds wonderful now. I wish everything in life was this simple. Since I am busy and not at all that technical, I would have not even attempted to fix this if it hadn't been for encouragement from the online community. I'm grateful to you all.

Chris Witmer
Tokyo

[JonMarsh]

Glad it worked out for you, Chris- sometimes simple solutions do exist!

~Jon

[cdwitmer]

Yeah, tightening up the loose screw worked so well that my wife suggested I try the same thing on myself.