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410 TVX Peavey stopped making sound

D

Diirt

Dec 4, 2018
3
0
#1
Hello there!
I have a 410 TVX cabinet and a Firebass 700 head (both Peavey)
I bought them used almost 2 years ago and all had been well!

The other day I was practicing and at one point it stopped passing sound. I tested my head and speaker cable on another cab and found nothing wrong. For good measure, I ran another head into my 410 TVX but no sound would pass.

I opened up the back to see if anything stood out as broken or blown but there was no visible indication of this.
However, I used my multimeter and discovered the input is being shorted to ground.

My first though was the input jack/switching mechanism was broken and causing the short so I removed it and found it wasn't responsible.

It's tricky to isolate the issue when your input voltages are grounded everywhere on the board and since I'm not familiar enough with amp repair, I don't know what to look for.

I started looking up some information on how to test transformers (and the other components in there) but didn't find many useful resources.

Does anyone have good resources or direct experience in troubleshooting this type of bass cabinet or testing the components inside the cabinet? Here is a link to the manual:
https://assets.peavey.com/literature/specs/00584220_3.pdf

Any help at all would be awesome!
Thanks
 
#2
Disconnect one lead from each of the speakers.
Use your Ohmmeter to test across each set of speaker terminals.
The reading should be just a little less than the speaker's individual, nominal impedance.
8 Ohm speaker, 5-6 Ohms on the meter. 4 Ohms... 3-4 and so on.

Also recheck to see if you still have a short at the jack with all speakers disconnected.

And do a battery test on each speaker while they are disconnected.

If you get proper Ohmmeter readings AND you get noise out of each speaker with the battery, then it probably usn't your speakers.

Does the cab have a crossover?

-edit- Just saw the manual you posted.
Crossover? Yep. Horn? Yep
Horn attenuator? Yep - Except it is not a pot in the general sense though it looks a lot like one.
 
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#3
I took the jack out because I thought it was shorting but it is not.

I did a continuity check between where sound comes in (the input pads where the jack was) to GND and there is continuity between those two points. There is also continuity between both leads in and out of the transformer. I don't think it's the speakers for this reason. Do you think it's worth checking the speakers if the short is happening on the board?

And yes it has crossover. I measured the pot and it yielded resistance on both ends when measuring from the wiper.
Though I am unfamiliar with how cross over circuit functions.
 
#4
Transformer? There's no transformer in that cabinet...

Troubleshooting involves systematicly testing and understanding what the testing means. Everything is logical.

Are you sure you are measuring a short? What kind of meter are you using.
 
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#5
Diirt said:
I took the jack out because I thought it was shorting but it is not.

I did a continuity check between where sound comes in (the input pads where the jack was) to GND and there is continuity between those two points. There is also continuity between both leads in and out of the transformer. I don't think it's the speakers for this reason. Do you think it's worth checking the speakers if the short is happening on the board?

And yes it has crossover. I measured the pot and it yielded resistance on both ends when measuring from the wiper.
Though I am unfamiliar with how cross over circuit functions.
Click to expand...
Measuring speakers with an Ohmmeter will yield very low results as I noted above. Measuring across the jack will also yield low results. This is why you have to measure each speaker with at least one lead disconnected from each speaker. When you disconnect the speakers you are able to check them individually without the other speakers or the crossover affecting what you see. Likewise with the battery test. That is a different way to check your speakers in case you are misreading your ohmmeter.

If the cab has a crossover then it should have a horn/tweeter or midrange speaker in addition to "big" speakers.

You can't reliably measure values with an ohmmeter while the device unde test is connected to other parts of the circuit. Just measuring things in a crossover while still connected may give you false readings.

EVERYTHING needs to be disconnected for individual testing with an Ohmmeter and battery test or you're just going to be chasing your tail. Disconnect the crossover from the speakers and disconnect at least one wire from each speaker to test the speakers by battery AND Ohmmeter.

Can you post a picture of the crossover?

Is "the pot" you say you measured really a variable L pad? This would be used to reduce the level to the horn/tweeter.
 
#8
Agedhorse, there is a large component that looks like a transformer. But as BogeyBass just mentioned, it may be an inductor. If you know a lot about amps and can see that I may be misidentifying something, instead of telling me there isn't one, you might be able to offer some insight as to what it is. Or even ask for a picture. This would be helpful in the process of learning.

I have little experience with amps so I don't know what is typical and what is not.
I build and repair synthesizers as my occupation, which I felt weird mentioning earlier... I am familiar with systematically testing things when troubleshooting. This is why I removed the jack and tested it out of circuit. Mostly I am interested in knowing what is typical in an amplifier and what is not. I'd like a good starting point and a reason as to why that is a good place to start.

I am using a common handheld DMM. It has an ohmeter, voltmeter, continuity (beep!) checker and many other functions, like most DMMs I've come into contact with. Is there a specific type of DMM you suggest?

Old Garage, are you saying it is normal for me to have continuity (~0ohms) between where the signal is coming in from my head and GND? Is this because the resistance is very low due to all the speakers being in parallel?

And so everyone agrees that if absolutely no sound is coming out of my cabinet, it is likely an issue with the speakers? Or is there any chance something else could be wrong. Again, any more information on the possible issues would be good. I am happy to test these things, but again, I like to understand why I am testing something and why someone thinks this could be the issue. So in this case, what could happen to a speaker that would cause the entire cabinet not to produce sound?
 
#9
I asked because some meters are terrible at reading low resistance. The D.C. resistance of the speaker should be about 60-70% of the nominal impedance.

If you understand how the crossover is supposed to work, and the components used, you can troubleshoot to identify what does not appear right in a step by step manner.

It could be a short circuit but that's not very common, and if it was a short I would expect your amp to be complaining.

Have you looked to see if Peavey has the service information available?
 
#11
The protection circuit is for the tweeter only.

Generally, where there is only one inductor present, and there are 2 caps (IIRC that's what this crossover has), it will be an 18dB/octave high pass filter with no low pass on the woofer. If there are 2 inductors present, that would indicate a low pass filter used on the woofer.

A bit of circuit tracing (don't go pulling parts off and making assumptions) will help you understand what kind of crossover you are looking at. From there you can make some better troubleshooting decisions. First you have to know how it's supposed to work, then you can test step by step to see what's not correct.
 
#12
There should not be a short to ground. I assume you touched your probes together to zero your meter.
Even if your crossover is a second order HPF, there are no inductors to ground from measuring at the jack.
You have to check each part by itself. There is no shortcut. A capacitor should not show an ohmage short condition.
An inductor will be nearly zero ohms. Each speaker will measure around 6 ohms. They should all measure the same resistance.
Your disconnected jack should not show a short from hot to ground.
I'm afraid you'll have to do the legwork. The good news is, you only have to disconnect one lead of a cap, inductor or speaker.
Nobody would know what your problem is without checking the parts.
To fix it, you must find out all the parts that are NOT causing the problem, and NOT try to get lucky by picking and choosing what you're testing.
That's why you cringe when you get a shop bill. By the time a tech disassembles and re-assembles a unit to check it out, and does some visual inspection for the usual (using experience), you already have some money invested.
There are so few parts in a bass cabinet with a crossover, it's time well spent to just check every part, because you could have multiple problems.
 
#13
Diirt said:
Agedhorse, there is a large component that looks like a transformer. But as BogeyBass just mentioned, it may be an inductor. If you know a lot about amps and can see that I may be misidentifying something, instead of telling me there isn't one, you might be able to offer some insight as to what it is. Or even ask for a picture. This would be helpful in the process of learning.

I have little experience with amps so I don't know what is typical and what is not.
I build and repair synthesizers as my occupation, which I felt weird mentioning earlier... I am familiar with systematically testing things when troubleshooting. This is why I removed the jack and tested it out of circuit. Mostly I am interested in knowing what is typical in an amplifier and what is not. I'd like a good starting point and a reason as to why that is a good place to start.

I am using a common handheld DMM. It has an ohmeter, voltmeter, continuity (beep!) checker and many other functions, like most DMMs I've come into contact with. Is there a specific type of DMM you suggest?

Old Garage, are you saying it is normal for me to have continuity (~0ohms) between where the signal is coming in from my head and GND? Is this because the resistance is very low due to all the speakers being in parallel?

And so everyone agrees that if absolutely no sound is coming out of my cabinet, it is likely an issue with the speakers? Or is there any chance something else could be wrong. Again, any more information on the possible issues would be good. I am happy to test these things, but again, I like to understand why I am testing something and why someone thinks this could be the issue. So in this case, what could happen to a speaker that would cause the entire cabinet not to produce sound?
Click to expand...
As was stated, some meters don't read very accurately.
I never said 0 Ohms. I said very low, and not because of all of the speakers being in parallel. I have no idea how they are wired. But because they may just be very low impedance speakers. This is also why I suggested that you measure the speakers while they are disconnected.

The very low reading may be misinterpreted as a short if you don't know the limitations of your meter.
This is why I wanted you to do individual battery tests on the speakers.

Before you get excited about no one explaining Ohms law to you before you start doing some of the things we suggested please realize that people are here to help, but if you need us to also hold your hand while we walk you to school you better let us know that up front. The education can get pretty scarce if you decide to crank up the disrespect by making demands of others who would otherwise be willing to try to help. You can't teach the fine nuances of every aspect of this stuff in a few posts. Be glad there are people who will try to help.

I'm willing to call it a clean slate and put any past attitude behind.
If that works for you, then welcome to TalkBass, what can we help you with.
 
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#14
agedhorse said:
Generally, where there is only one inductor present, and there are 2 caps (IIRC that's what this crossover has), it will be an 18dB/octave high pass filter with no low pass on the woofer. If there are 2 inductors present, that would indicate a low pass filter used on the woofer.
Click to expand...
I have one and yes, it has a low pass filter on the 4x10's. Most folks remove it to give a more modern sound - mine came free with the tweeter pre-blown so needed that done anyways ;)
 
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