2000 Limited Subwoofer/Amp issues

[BradyGoat]

Hey Guys,

Yesterday when I started driving I noticed that I wasn't getting any bass from my Sub.... I had time later to take the rear plastic off and see what I could see inside the panel. Wiring looks good, I'm getting 12V on the wires to the amp, but I'm not really sure how to test the two wires that go into the connector connected to the subwoofer.

You can hear a TINY bit of bass to the sub if your ear is right on it. Not sure if this tells anybody anything. Not sure where to start. Don't know if it's the amp, sub, or possibly the head unit itself. Any ideas of where to start?

 

[Mbrooks420]

Most likely the speaker or amp. I’d pull the wires and hook up another speaker to test the amp. If that works, test the speaker on a different source or channel.

 

[J_C]

With music playing at a fair volume, the amp should be outputting well over 1V AC to the sub speaker. Of course this reading will be changing on the multimeter as the song notes change, unless you're feeding it a continuous low (enough) frequency tone but for this basic test that isn't necessary, you just want to see if the amp isn't outputting versus the speaker coil being fried. You can measure this with the amp still connected but to be sure you'll need to measure with it disconnected from the speaker.

You can also measure the resistance of the speaker coil. On a custom setup like that I shouldn't guess what impedance it has but should be in the ballpark of single digit, perhaps 4 ohms.

Swapping the speaker is easy. Troubleshooting the amp I can possibly assist with but it gets much more complex, tracing audio signals starting with the assumption that the most likely part of the amp to fail would be capacitors or the last stage in the output, transistors whether discrete or built into an amp IC. Pics of the amp PCB might help.

If the speaker coil is shorted you really shouldn't leave it connected and use the stereo. Disconnect the sub speaker if you need to continue to use the stereo until you have time to fix it.

 

[GLOCKer]

The sub in my 1998 Limited sounds very quiet too. I considered replacing the speaker, but I'm not sure I want to tear out the interior to get to it. If I remember correctly, there is a lot of stuff that has to come out to get it, no?

 

[J_C]

The whole side panel comes off then the whole assembly comes out. It's not that bad, especially if you consider it doesn't leave the vehicle undriveable to have it apart.

 

[GLOCKer]

The whole side panel comes off then the whole assembly comes out. It's not that bad, especially if you consider it doesn't leave the vehicle undriveable to have it apart.

Oh wow! I thought you had to do more to get it out!

 

[BradyGoat]

Finally got around to tackling this project.

Since this happened back in May, it has randomly come back on and worked again for 2 days, then quit again.... I don't think it's the wiring, I think it's the amp. I found a used amp on ebay for 50 bucks that I am going to swap in. I think it'll solve my problem, but if not, I think I'll give up, because I don't really want to deal with wiring.

It's amazing how good this 20 year old sound system sounds when it's working. I didn't think I'd care about the sound in my "winter beater" but not having that sub has made driving less enjoyable. I hope it's the amp!

 

[Turdle]

Don't waste time or money trying to make the stock sub sound better by purchasing a better driver. It's the amp. No response below 100 hz for the most part and very low 25w power.

I once connected 2 - 12dvc image dynamics subs to the stock unit with no audible difference. They are very efficient, and, with just a punch 60 wipers would bounce on the windshield.

 

[BradyGoat]

I just got a used factory amp. I was more than satisfied w the stock sound.

 

[BradyGoat]

Update: new amp didn’t fix it.... I guess it’s possible that amp was bad too? I doubt it.

I can hear the sub pop a little when I turn on the key....

Is if possible that it’s the head unit? It doesn’t light up at all and the digital read out is dead, so i did order a new one of those too.. but it does function other than I can’t see what I’m doing.

 

[J_C]

When music is playing, use a multimeter in ~20VAC range to measure for voltage on the red/black and brown/orange wires going to the amp. That is the audio signal going to it. If you have no signal getting to it then it's the head unit or wiring between the two that is bad.

NOTE that this assumes you have a system with just the sub amp at the sub, not the amp for everything outside of the head unit. If you have just the sub amp then you have approximately 5 wires going into it and two going out to the sub. If it is instead the amp for everything, it has closer to 19 wires but I don't see a sub hookup at all for that.

If you have signal going to it but nothing coming out to the speaker, then the amp itself is bad.

If you have signal coming out to the speaker but the speaker isn't producing sound, it probably has a fried coil in it.

 

[BradyGoat]

When music is playing, use a multimeter in ~20VAC range to measure for voltage on the red/black and brown/orange wires going to the amp. That is the audio signal going to it. If you have no signal getting to it then it's the head unit or wiring between the two that is bad.

NOTE that this assumes you have a system with just the sub amp at the sub, not the amp for everything outside of the head unit. If you have just the sub amp then you have approximately 5 wires going into it and two going out to the sub. If it is instead the amp for everything, it has closer to 19 wires but I don't see a sub hookup at all for that.

If you have signal going to it but nothing coming out to the speaker, then the amp itself is bad.

If you have signal coming out to the speaker but the speaker isn't producing sound, it probably has a fried coil in it.

Yeah, it's just the amp for the sub... Since I have a new head unit coming soon that I have to replace anyways, I will wait to rip open the side panel again until I find out if maybe it's the head unit.

I'm not really familiar with this audio stuff as you obviously, if it was a bad coil in the subwoofer, would it randomly start working a day here and a day there and sound like a million bucks?

 

[J_C]

^ Once the coil is shot it will "usually" not recover. There is some slight chance the coil insulation shorts out with changes in temperature but that is far less likely than two other possibilities which are a bad connector, or a bad solder joint on the amp board. It's less likely than the head unit having a fault too but if you play odds and likelihoods too often, you can end up chasing your tail if you don't have the most likely fault.

It's most useful to use a multimeter to measure where the audio signal stops (or at least drops to a very low AC voltage) in the chain while it's happening.

If it's just a bad amp board solder joint, that's something cheap/free and easy to fix if you can solder. The usual places to start there are look at areas on the PCB that are discolored from heat and the solder joints associated with those areas, and any large power resistors, transistors or amp-IC chips, though in an automotive environment it can be vibration as well as heat that contributes to broken solder joints. If it has short circuit protection relays, check input vs output voltage (while playing music of course) on the switched contacts on those too.