Vintage - Rockford Fosgate Problems

[MrGeekFreak]

I received a Rockford Fosgate amp from a friend last week. I had it wired in my sister's car for around 2 days, running a 10" subwoofer. It worked perfect up until tonight when her car's battery died while her friends music playing.

So I plugged in my battery charger, set it to 2 amps, and let it sit for about 20 minutes. When I came back, her car started, but the amplifier wouldn't work. The red power LED comes on, but there is no output. I've tested multiple working speakers and nothing happens.

I would really appreciate some help, as she is leaving for college very soon and I want it to be working. I understand it's an old amp, but it's all I've got for now.

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[MrGeekFreak]

I busted out my trusty multimeter last night and the car's battery was only at 11v, but the amp's operating voltage is something like 9v to 17v. So I think that rules the battery out.

I also tested the remote and power wires and they read proper voltage levels. At that point, I was getting a little annoyed, so I ripped the amp out of the car and hooked it up to a PC power supply. The amp started working right away with my car's subwoofer.

So I've narrowed it down to something in the car. If anyone has had similar experiences and knows the problem or even has an idea, I would REALLY appreciate it!

 

[sacsking916 5,000+ posts]

did you check your fuses in the power wire? or on the amp itself?

 

[Bassin Buick]

did you check your fuses in the power wire? or on the amp itself?

probably no fuses in the amp , most of the old RF's didnt have fuses.

 

[candeshop407]

rca voltage checked with the multimeter?

 

[akheathen Premium Member]

what model amp is it, first off....... some circuitry, for whatever reason, i have seen the amp just need a discharge and then hook back up to start working again.

 

[MrGeekFreak]

Oops, I forgot to say that it is a 4.6x Fosgate. In the car, its hooked up with the high level inputs and I also tried the RCA in there, both of which didn't work. When I took it out and plugged it into my computer PSU, the RCA worked fine.

The inline fuse is still intact, and I don't see any on the amp itself. I also checked everything else inside the amp, and nothing looks blown. A friend I suggested that the ground on the car may be bad, but it was just working a couple days ago, so I don't think it would be the culprit.

 

[akheathen Premium Member]

use an mp3 player on an rca-to-3.5mm headphone adapter....to rule out that, and yes, bad ground can still work, but will cause problems. best thing is to take a voltage r3eading right at the amp terminals, and between pos, and bare metal, to check the ground, and measure voltage at the amp, vs at the source (battery) while it is on. have you tried putting it back in the car?

 

[MrGeekFreak]

use an mp3 player on an rca-to-3.5mm headphone adapter....to rule out that, and yes, bad ground can still work, but will cause problems. best thing is to take a voltage r3eading right at the amp terminals, and between pos, and bare metal, to check the ground, and measure voltage at the amp, vs at the source (battery) while it is on. have you tried putting it back in the car?

I did use one of those adapters when it was being tested in the house and while it was still working in the car. It was fine then. I dropped the amp back in her car this morning and checked the voltages on the amp terminals again.

The battery itself and the amp's terminal were something like 12.8v, the remote was around 9v, but I didn't check the ground's bolt directly. The voltages, while a little bit low, sound about right to me.

She told me that there was still no output from it today, so I guess I'll have to try something else when she gets home.

 

[MrGeekFreak]

Alright, I tested the amp while the remote switch was on, and I only read 8v on the postive terminal. I also checked RCA voltages and the front left channel (the one I was using) was putting out .45v.

I'm not very experienced with car audio, so what could the low voltage on the terminal indicate?

EDIT: Even if the car is turned off and my remote switch is turned on, the battery terminal on the amp only shows 8v

EDIT EDIT EDIT: It was an improper ground! Thanks to all that replied!