testing a crossover

I agree with MC's dead short analysis. Are you b-amping using the passive crossovers inside the speakers, or are you using an active crossover at the inputs of each amplifier? If you are using the passive crossovers in the speakers, then there could be a short in the crossover. But, that doesn't explain why it works when you go back to driving with a single amp. Let me think, and I might have more suggestions once you get back to us.

Okay so MC said bi-wire and not bi-amp, big deal, I knew what he meant. At this point we know there's a short somewhere. Could be shorted caps, but we need more info.

@likklegerry - Anymore info from you? Are you using internal passive crossovers?

I would like to help as I'm an avid bi/tri-amper. I would guess you've checked the cables and wiring to the amp and speakers? I don't know anything about the crossovers in the speakers, is it possible to draw a schematic or shoot some photos? I use an active crossover at the inputs of my amps to limit the frequency range to each driver, tri-amping. Nothing but wire between the voice coils and amp outputs. This configuration virtually eliminates intermodulation distortion, which is most offensive to the ears. I've been bi-amping for 44 years and tri-amping for 41 years. Might be as simple as bad caps in the crossovers you are using. If you would like, I could send a PM to you with my email and you could send me a schematic or photos of your speaker crossovers. I'm positive we can get to the problem without much effort. 

Thanks imhififan, I didn't know that either. One other thing I thought you should check on both amps, both channels. How much DC voltage is present at the output terminals?

The reason why the speakers work with a single amp and not when bi-amped is because the crossover is using different sets of inductors and capacitors. When the speakers are bi-amped you are using one set of inductors and capacitors, those are the caps or wiring that has the problem. The inductors are not the issue in my opinion. The wiring is suspect, if the caps test good. Think about what I've said thus far and tomorrow we'll get into the testing if you insist on repairing these crossovers. At this point, I don't think it's necessary for you to measure the DC at the amplifier outputs although that is always good info.

I just looked at all of your crossover photos. Don't take the following comments the wrong way, but this is my honest opinion. You should take those crossovers out and tri-amp with an active electronic crossover, please. You will truly be amazed at the improvement in sound you will get. Those are pretty cheap crossovers as the inductors are wound on ferrite and should be "air wound" on bobbins. The wire they are using for the inductors is Way to small and likely sucking allot of power from the drivers. This was a cost cutting decision when they were designed. No matter what you decide, I will help you get your speakers up and running again, bi-amped or tri-amped, whatever you decide. I'm going to take a close look at the measurements you posted the other day and all the pictures again. Will come back with questions and probably additional tests to perform. Did you ever measure the DC voltage at the amplifiers outputs with nothing connected and no signal input? Did you get the damaged amp back repaired yet? 

Did you change all of the capacitors yourself? The caps look like they are good quality.

No NOT ac voltage, DC voltage. This is the offset voltage of the amp and I wanted to make sure they were low as THAT could be a cause of capacitor failure.

Well if you have lifted one lead of each cap and they test good, I would say it's a short on the PCB. Check all the resistors just to be safe, most resistors open or go high when they fail. In one picture I saw a couple capacitor leads that looked very close together. On another note, you said the amp worked for about 3 hours when you first got it back. So I'm assuming they sounded good when bi-amped before it went pop? I'm thinking there could be physical contact between a couple components lead wires. Reason, it work for a while. Maybe vibration caused the components to get physically close enough to short. What is the value of the cap connected to the midranges in the bi-amp configuration?

For some reason I can't access your crossover photos I saw yesterday. Anyone else have this problem?

erik - If you are not really going to try and help, stay out of it! Dude...

I just looked at the crossover too, not good. Would be very easy to create a disastrous mistake, not to mention the EMI and RFI problems. Heat is not a friend of caps as you know.

pragmasi - I agree, rule out the simplest possible problems first. That's why asked about cables and connectors. Did we ever get an answer about that? I'm going to look at the schematic now. Good luck!

I can guess, but that would be uncalled for and premature.

pragmasi - Yes, sorry for being an SA. You are absolutely correct, one needs to take one step at a time. I'm waiting to see and help if possible.

Which resistor, if it's STILL showing a dead short or 0.00 ohms? This is the one mentioned in post 6-16 @ 12:59am

Okay, its been a rough couple days. I just got done drawing the schematic and looking at the words and measurements again. Just one note, do all measurement in the resistance mode, not in the diode mode as the diode mode really doesn't tell us anything. You don't need to disconnect one end of the resistors to check each resistor. So with no drivers attached, between the midrange terminals on the crossover board, you get close to 2.2 ohms, but it's not a dead short correct? For the tweeter terminals, you get close to 0 ohms, but not a dead short correct? At the mid/hi amp inputs, you get essentially OL after holding the probes on the terminals for few seconds, correct? What happens when you reverse the leads on the mid/hi amp terminals? Does the meter go to (-) xxx.x ohms then to (+) xxx.x ohms before going to OL? This is a dumb question, but just so I understand everything. When you use only one amplifier to power the speaker in the full range (bi-WIRE) mode, the (+) terminals of the inputs are connected together. And separately, the (-) terminals of the inputs are connected together, correct? The photos are gone, but don't think we need it again. From your DC voltage measurements at the amps, they look healthy. Please answer all of my questions in order, so we don't get confused, thanks.

CORRECTION, sorry. The last test on the mid/hi amp terminals on the crossover board; when I asked to to test and then reverse the meter leads and test again. The multimeter should be set on the "diode" test mode, not ohms. The readout should display some voltage then go to OL. When you immediately reverse the leads, the display should read -x.xxx volts, then change to +x.xxx volts before going to OL. Hope your meter has a diode test function, but it's not absolutely necessary. This test just shows that the caps are charging in both directions.
I still can't explain why the system worked with one amp when the mid/high amp was in repair... This is troubling. 

The testing of the mid/hi input terminals showed the caps at that end of the circuit were charging and discharging. No shorts or problems were noted in that particular test.

I'm curious, do you have a list of parts that were replaced when the amp was serviced? A list from the first repair and one from the second repair might shed some light on a potential cause for the failures.

pragmasi - I assume your post above was meant for me? I guess I really didn't need an answer to the last 2 sentences of my above post because I'm sure the answer is really yes, and maybe confusing to some.
You are absolutely correct about forgetting the jumpers when switching from bi-wiring to bi-amping. That could easily blow one or both amps used in a bi-amp configuration.

likklegerry - Thanks for your test data, looks like everything except the Lo and Hi bi-wire connections are in line with what I expected. Just to be clear, with the amplifier and other electronics off, an ohm meter test between the HF+ and LF+ terminals should be 0.0 ohms. Same should be true of the HF- and LF- terminals. This can be measure at the speaker or amplifier terminals.
The diode mode tests at the HF and LF connectors also show what I was expecting.
The dc resistance measurements with the drivers disconnected are in line of what is expected too. Don't worry if it's mH or not, trust us, it is mH.
Which capacitors (value) is showing shorted in the diode mode? The caps themselves should be tested in the ohm mode. I will continue reading an ask questions or make comments as needed.
Please do the resistance test between the HF and LF terminals as described above. This is in the bi-wire configuration with all wires connected to one amplifier.

likklegerry - Just forget that question, I already understand. Providing your crossover passed the test using the diode mode at the mid/high bi-amp inputs, which it appears to have. I think you are good to go. Just perform that same test with the drivers connected. I'll get back in touch later today.

Stop, I would not strip any parts off either board. The data, answers to my questions, looked promising. You’ve already done a lot of visual inspection and testing. The most recent pictures, the cap with the blue circle around it, what is that? Suspect bad part? What is the printed value of the cap including the voltage rating?

In one photo I can read 3.9uf/250V. When you drew and label the components on the circuit board the 4.2uf should have been 3.9?

I didn't know you were in Bulgaria, that explains the delays in communication. I think a few more tests are the only thing that is required to conclude that the issue is solved. I'm still willing to try.

I don't believe there is a problem that exists on the crossover any longer. Let's just do a few more tests. 

The fact that the speakers and amps worked of a couple or more hours is a hint that the problem may not be in the crossover. Are you SURE that when you bi-amped the speakers after getting the amp back from servicing that you didn't forget to remove the second set of cables to the low and mid/hi inputs? If the amps were connected in the outputs, even just one wire like the negative or positive between amps, that could have caused the amplifier failure.

rodman - Just FYI, I did explain that the diode function test was to verify the charging and discharging of the capacitors. This was in my post of 6-16 @ 7:06pm. His answer showed there was no longer a short at the inputs of the mid/hi amp connections.

Here are my posts from that day:
06-16-2021 5:40pmOkay, its been a rough couple days. I just got done drawing the schematic and looking at the words and measurements again. Just one note, do all measurement in the resistance mode, not in the diode mode as the diode mode really doesn't tell us anything. You don't need to disconnect one end of the resistors to check each resistor. So with no drivers attached, between the midrange terminals on the crossover board, you get close to 2.2 ohms, but it's not a dead short correct? For the tweeter terminals, you get close to 0 ohms, but not a dead short correct? At the mid/hi amp inputs, you get essentially OL after holding the probes on the terminals for few seconds, correct? What happens when you reverse the leads on the mid/hi amp terminals? Does the meter go to (-) xxx.x ohms then to (+) xxx.x ohms before going to OL? This is a dumb question, but just so I understand everything. When you use only one amplifier to power the speaker in the full range (bi-WIRE) mode, the (+) terminals of the inputs are connected together. And separately, the (-) terminals of the inputs are connected together, correct? The photos are gone, but don't think we need it again. From your DC voltage measurements at the amps, they look healthy. Please answer all of my questions in order, so we don't get confused, thanks.fiesta75404 posts06-16-2021 5:48pmWhich resistor, if it's STILL showing a dead short or 0.00 ohms? This is the one mentioned in post 6-16 @ 12:59amfiesta75404 posts06-16-2021 7:06pmCORRECTION, sorry. The last test on the mid/hi amp terminals on the crossover board; when I asked to to test and then reverse the meter leads and test again. The multimeter should be set on the "diode" test mode, not ohms. The readout should display some voltage then go to OL. When you immediately reverse the leads, the display should read -x.xxx volts, then change to +x.xxx volts before going to OL. Hope your meter has a diode test function, but it's not absolutely necessary. This test just shows that the caps are charging in both directions.
I still can't explain why the system worked with one amp when the mid/high amp was in repair... This is troubling.

rodman - I appreciate your comments. I just don't want the OP to do anymore work on the boards before doing tests. It seems like he is doing rework in the middle of the tests and that could make some tests invalid. This could create more problems as I'm sure you know. The only test I want from him before finalizing everything is the dc resistance across the tweeter terminals of the board, because his last info on that makes me think the resistance he measured was below what I expected from a 0.22 mH inductor. All help is welcome.

imhififan - That was very helpful, thank you!

**likklegerry - Small difference between the original capacitor values and the ones you installed will not cause failures of the amplifiers. If anything, it would have a SLIGHT chance to damage the tweeter or midrange driver. Since it appears that the value of the original capacitor for the tweeter was 4.2uf and the one you installed is 3.9uf, that would very slightly raise the crossover frequency and absolutely NOT cause damage to the tweeters or amplifier. The caps you installed will definitely improve the sound, so please just leave them in.

imhififan - That is an excellent catch. I was beginning to think along with rodman, that maybe the problem was outside of the speaker crossovers. I think you may have nailed it. I suppose the single short could have caused both channels of the amp to have failed, or maybe the other board has similar issues? I have asked OP about a list of parts that were replaced when the amp was serviced, wonder if he has that info. What do you think about the lower than anticipated resistance measured across the 0.22mH inductor?

imhififan - I agree on both suggestions. I just recently learned that iron core inductors are suppose to be better than air core for the bass driver due to the lower dc resistance in many cases. Tannoy  is one that uses iron core on some speakers, I'm still learning... He wouldn't even need to make a PCB, he can just use point to point wiring for those 2 components and that would also reduce the dcr.

Lower than expected dcr for 0.22uH inductor; from what I can tell, a nominal dc resistance for that inductor is about 0.21 ohms. Think that is one area that needs some additional testing.

Yes, thanks for the links, info and your input. To me, it looks like the wire gauge is 22 or 24. Doesn't appear to be 18 for sure, but hard to tell.

Correction to my post deleted. 1/Lt = 1/L1+1/L2... So yeah, dcr is about 0.05 ohms or less. Initially thought it would be about 0.68 ohms, but that was incorrect.