car stereo trouble

[mattmcl]

I figure someone on here might know something...

I have a Pioneer in-dash receiver with 3 sets of stereo RCA outputs. The subwoofer set goes to an amp under a seat, then to the sub. The other 2 sets are front and rear, which all go to a 4-channel ump under another seat, then to crossovers, and finally to the speakers.

All of a sudden, when I start the car the stereo wouldn't play. If I turned it way up, I could hear the music but it was very crackly. After driving about 10 minutes, sometimes the music would come on slowly and be fine until I shut the car off again. A week ago it just wouldn't come on past the crackly low-volume signal. The amps under the seat light up, so I know they're getting power.

I took the dash apart and ran each of the RCA outs on the preamp through a home stereo receiver- good strong stereo signal from each. I checked all my fuses, checked continuity from each amp to ground, and removed the wiring harness adapter for the receiver and soldered up just the right (battery), yellow (switched), black (ground) and blue (remote turn on for amps) wires directly. I checked continuity on the blue wire to the amps as well.

So the receiver is getting power and outputting sound.

The amps are getting switched on and are grounded.

It could be the RCA cables, but each of six cables would have to have failed. Could be blown speakers, but again all six speakers plus the sub would have to have failed. The amps could bad, but it would have to be both of them.

I'm at a loss. Any ideas?

 

[Bassman]

It sounds like your receiver is not putting out sound until it warms up. This happens on my home receiver. This isn't a problem for me because I leave the receiver on, but you cannot do that.

What I would do is try to find out what level the receiver outs out and get a boom box or mp3 player that is at a similar level, hook that up to the amp and start with the output volume all the way down. Slowly raise the volume until you hear audio. Try to not start the car until you are fully ready to check. That should prove that it is your receiver.

I'm basing this on how I am understanding your setup. But my guess is you need a receiver. It may not be worth fixing.

 

[jevehn]

Even though you checked it, my first thought on there is bad ground. Are both amps grounded out to chassis at the same spot? if so, is it corroded or clean?

Where is the deck grounded to? Under ideal circumstances, I usually recommend chasing a small wire between deck ground and amp ground to ensure common ground. That way RCA can reference signal to a common ground.

Unplug the left (or right) RCA, and see if you get anything. Maybe you have a polarity issue. That should be apparent right from installation, but it can't hurt to verify.

Otherwise you're chasing a ghost. If you find the problem please post it, as I'd like to know what it was. Curiousity is a dangerous thing

Another thought: Could be your deck. You could have a weak solder joint on an SMT chip deep inside the head unit. Poor connection until it heats up, and then ok. Works if you shake it, but only sometimes. Take you deck out of the DIN bracket and try tapping it while playing. If that turns out to be it, it's a good excuse to go by a new one

 

[wildwest450]

I would double check grounds also. They will do strange things when not properly grounded.

 

[buffalobrewer]

I'd check the neighbors. they probably did something so you would be out of earshot before you start cranking the tunes.

 

[Fingers]

A common problem is with cold solder joints. They wave solder the board and if the temp isn't quite right, some joints don't make a good connection. As the car and the equipment warms up, the joint expands and makes connection. The sound you're hearing is likely the pre-amp stages leaking through the power amp stages. Once the unit heats up, the power amp kicks in and away you go. Once the equipment cools down the joint shrinks and loses connection.

The remedy is to open the equipment up and re-sweat all the joints. It's labor intensive but if done properly you won't do any damage. Use a nice hot iron and 'quick in and quick out' to keep from heating components or board traces too much.

 

[mattmcl]

Wow. Great advice.

I'll try grounding the receiver to the amp ground, that could be it.

Yeah, I'm thinking I might have to crack the case though. I think I know where to start, too. The pin that the remote switch wire connects to is a bit loose, just noticed that after I posted here. I've built audio components, I can solder SMP and PCB stuff no problem.

Now, as I understand it, that blue wire from the receiver supplies a small amount of current to tell the amps to turn on. What if the amps were only getting a fraction of the current it should? The amps can't "sorta" turn on- it's either on or off, right?

 

[Bassman]

The reason why I would think that it would not be a cold solder joint is that after the receiver has warmed up it is still being bounced around and I would think you would still have some intermittency. The OP is saying it is fine once it warms up, not intermittent. Also when it starts he is getting very low, distorted, audio, not intermittent audio.

 

[jmendez29]

Can we assume that this is relatively new aftermarket equipment? Do all of the speakers come on at the same time or does one set come on after another? It seems to me that the common link is the head unit. To test problems like this in the past, I just used a CD player or even an MP3 player with a stereo input cord (has the speaker plug on one end, and the RCA plugs on the other end) and plugged that into each amp. Its a little bit lower of an input voltage but it should still give you some good solid sound out of it, at least enough to let you know if the amp is the problem.

And the blue wire is definitely a switching power supply. I've never heard of anyone with a "partially on" amp because of the switching.

 

[jevehn]

The remote wire (blue), is all about voltage, almost no current. Most modern amps are switched on via a Mosfet, which has a very high input impedance. As long as your reading 12 Volts between remote and ground, you're good to go.

 

[mattmcl]

So I dove into it this weekend. Started checking every single fuse, contact and component. Got through testing the head unit and plugged it all back in, and figured what the heck, let's see what happens. The whole system fired right up. I did about 4 hours of driving this weekend and everything was fine.

Not that I'm complaining, but it would have been nice to figure out what was causing it. Maybe a loose fuse or something.

 

[GilaMinumBeer]

First, I'd get the ump out from under the seat.

Second, I'd return that receiver.