Cerwin Vega V30X speaker cabinet

[Helmholtz]

Helmholtz, Indeed, the 45 resistor and choke ARE out of the circuit in normal mode. Look at the connections to the relay contacts. The 45 resistor is shorted in normal mode.

You're right, I missed that the 45 Ohm resistor is shorted by the relay in normal mode. But the choke always stays in circuit as it's wired to ground and acts in parallel to the tweeter. So the rest of my interpretation is valid.

[johnhoef]

Helmholtz, Ha! You're right, indeed the choke does stay in the circuit...my mistake.
Anyone out there care to make an educated guess as to the value the 6.5mfd cap should be? Should it be, indeed, 6.5?

[Helmholtz]

The ideal values of the caps depend on woofer and tweeter properties (crossover frequency) as well as the choke's inductance. I don't feel able to make an educated guess.
Is this a stereo pair of cabinets? If so you might open the other one and hope that that has caps with better readable prints.

Very strange that this kind of caps actually failed. And even both of them. What are your meter readings? Did you check with known caps that the meter is working properly?

[nevetslab]

The ideal values of the caps depend on woofer and tweeter properties (crossover frequency) as well as the choke's inductance. I don't feel able to make an educated guess.
Is this a stereo pair of cabinets? If so you might open the other one and hope that that has caps with better readable prints.

Very strange that this kind of caps actually failed. And even both of them. What are your meter readings? Did you check with known caps that the meter is working properly?

In lieu of a capacitance meter, connect an oscillator to one end of the cap, a 100 ohm resistor at the other end and ground the resistor to your oscillator's ground, and sweep the frequency....an AC meter will do fine here. Say, 1V input. 1.5uF with 100 ohm resistor will yield a -3dB corner @ 1.06kHz. @ 503Hz, the output should be 6dB down, at 251Hz it should be 12dB down, and so on. Then, remove the 1.5uF cap and install the other cap who's value is really not known. We're assuming the value to be higher. If, say, it was 6.5uF (not a standard EIA value, but so what), you'd get a -3dB corner at 245Hz, and at half that frequency (126Hz) -6dB, half again (63Hz), -12dB and so on. That would verify the caps are good or not, and, from the known shunt resistor value (100 ohms), you can calculate what the cap value is (C = 2/(F*2*pi*ohms). Using 1V, -3dB would be 0.707V, -6dB would be 0.5V, -12dB would be 0.25V.

[g1]

I won't speculate on the value of the cap at all.
But I will say the digit in question on that white cap appears to be either a 3 or an 8.

[J M Fahey]

What does "bad" exactly mean?

Open? .... Shorted? ... WEIRD capacitance shown? (as in 200pF or 50uF or some other impossible value).

Did you use a capacitance meter or just an ohm meter?

[johnhoef]

Nevetslab, Thank you for the test procedure for testing these caps. I am well aware of this procedure. Suffice it to say, I have determined without any doubt that these two caps are bad, and need replacing. So, my problem is determining the value of the white cap. Since it is defective, there is no way to measure it's correct value. They are both open, so my capacitance meter shows either open or very low capacitance.
This crossover, as a reminder, is from a Cerwin Vega V30X speaker. This is a professional high wattage speaker used on PA systems for VERY loud performances. No doubt some clown was not aware of it's limitations, and cranked it up!! After some time, the caps decided they had enough of this. I think the defective caps simply failed in time due to the stress they were exposed to. My guess is one of them failed, so the other took the remainder of the brunt keeping the tweeter going, until it finally failed, at which time, the clown noticed no more high end.
G1, indeed, by process of elimination, I agree the only two possibilities for that unreadable digit is a 3 or 8. If this is the case, I would lean towards the 8, as 3 would bring the crossover frequency too high, in my opinion.
Helmholtz, yes, indeed, this speaker is one of a stereo set. I have already contacted the customer to bring me the other crossover. Crossing my fingers that this other crossover has at least the white cap intact so I could either read it's value, or measure it. Also, I figure as long as I have that other crossover, I may as well recap that one. No doubt is was subject to the same stress!

[johnhoef]

I received the other crossover from the customer. It is in working condition. I promptly measured the capacitors. The 1.5 is indeed 1.5. The larger white cap measured .6mfd. This surprised me. I was expecting something larger. So, wondering if this cap has drifted far out of range. The markings on this cap are ever worse, and totally unreadable. However, this crossover does work, and the tweeter is tweeting!! Well, unless I hear otherwise, I will replace with the values discussed earlier - 1.5, and 6.5, 100v.

[Helmholtz]

I received the other crossover from the customer. It is in working condition. I promptly measured the capacitors. The 1.5 is indeed 1.5. The larger white cap measured .6mfd. This surprised me. I was expecting something larger. So, wondering if this cap has drifted far out of range. The markings on this cap are ever worse, and totally unreadable. However, this crossover does work, and the tweeter is tweeting!! Well, unless I hear otherwise, I will replace with the values discussed earlier - 1.5, and 6.5, 100v.

If the other speaker works fine, there is no reason to use larger cap values. It is improbable that theses foil caps drifted. In fact higher value caps will pass more mid range power to the tweeter, so the lower ones are safer.

[J M Fahey]

I received the other crossover from the customer. It is in working condition. I promptly measured the capacitors. The 1.5 is indeed 1.5. The larger white cap measured .6mfd. This surprised me. I was expecting something larger. So, wondering if this cap has drifted far out of range. The markings on this cap are ever worse, and totally unreadable. However, this crossover does work, and the tweeter is tweeting!! Well, unless I hear otherwise, I will replace with the values discussed earlier - 1.5, and 6.5, 100v.

And WHO said it was actually 6.5uF or anything else for that matter?
You pulled that value out of the blue and actually have no clue.
No "discussion" determining that value and if anything considering it unlikely (to put it mildly)

the one I labeled 6.5mfd (a guess). Or if anyone here can tell me what you think it should be?

[johnhoef]

JM, thanks for your scolding! Indeed, the 6.5mfd figure is one I pulled out of the air, based on my experience working with crossovers. And, Helmholtz, I agree with you, since the other speaker works fine, the .6 mfd cap is probably correct. Since the readable portion says X.5, I'll assume it's a .5 mfd cap. And indeed, that value will spare the tweeter from a wider frequency band....OK, 1.5, and .5 it is!
Thank you all for your help!!

[J M Fahey]

JM, thanks for your scolding!

Oh, no scolding at all , just trying to help you repair properly that fine speaker.
I fear too low a crossover point (because of a too large capacitor) will soon blow it to pieces.
Take care friend

[johnhoef]

JM,
Of course....I appreciate your wisdom. Sometimes it is not prudent to make assumptions. So, including the corrected schematic here one more time for anyone out there that is attempting to repair a Cerwin Vega V30X....

[J M Fahey]

Looks reasonable, it offers some fine tuning of crossover frequency.
Not dramatic, but should be heard.
Specially if at that particular frequency there is a strong peak or notch (speakers have wild curves) so "a few Hz up/down" might have a significative effect, at least with the original driver.