timjohnson

Hi guys got a rockford fosgate amp and alpine sub, 4 some reason now wen turn stereo on the amp powers on but no sound from sub ! if u unscrew speaker cable then just touch it against ternminal it sparks then sound comes out ! ive looked at ALL connections now im totally baffled !!!! any ideas ? tested sub on own, fine, thinkin amp ?

Big_Dan531

sounds to me like ur RCA leads are knackard try a new set on there it could make all the difference

timjohnson

hmm bout the only thing havent tried yet ! will test them next, hope not in a way as all under carpet and seats !!!

richardg

knock up a temporary cable from speaker cable and cheap plugs from maplin. if it works, you know what you have to do. if it doesn't, at least you haven't had to remove the rca cable

timjohnson

yeh will do , ill test that next , just find strange the way sparks when touch speaker cable against terminhal then will play ! then wont after a power off ! hmmm

timjohnson

nope ! thats the rca's now changed and still same & speaker cable. really thinkin now just maybe an earthing prob , think need to test nuther amp ! grrr

timjohnson

another amp tested with my wiring - perfect so some sort of remote prob on my amp but dont know anywhere (fairly cheap) that repairs them ! anyone help ?

timjohnson

bttt

timjohnson

been off 2 repairers twice & still same ! any ideas anyone !! ? rockford want £100 2repair

shanew

Out of interest have you tried another sub, it's possible that the cable to the sub may be damaged, either the cable to the box or the internal cable that goes from the terminals on the box the the sub it's self. A simple way of checking the amp is working correctly is to put a multimeter on the speaker terminals with the meter set to AC, typicaly a 500w RMS amp should show you around 20 - 25v ac. you'll find it easier for checking if you use a test tone, you can download one from the net as an mp3, burn it to a cd and play the track continuously, look for one in the mid 30hz's. you can use a normal music track but as the music changes the output of the amp will be all over the place and make it hard to measure

timjohnson

yeh that was one of my 1st thoughts actually but ive been runnin friends amp in it 4 over 2weeks not one problem at all !

shanew

Is the amp going into protect mode? RF's used to have a red led that came on if it did, it's possible that something is triping it on power up. It's difficult to pin this one down as if could be a few things.

Few questions that may help work out where the fault is:
Is this a new install or have you been running the same sytem for a while?

When the amps been taken in to be checked have they returned it as no fault found?

timjohnson

its got the red led on , but next to it just says LED, they said they found some dry joints and re-soldered! but worringly 2day i felt the earth cable and its stupidly hot ! which eath cables dont get ! but fine on friends amp again and yeh the system was fine before been insatlled three years !

shanew

Dont be over worried about the cable unless it's really hot, the harder the amp works, the more current it draws and as this is what causes it to get warm. the red led means it's in protect mode, so it's one of a couple of things, Worst case is that the output stage of the amp is faulty, usualy one of the mosfets or opamps have gone, this is usualy easy to see, it you unscrew the bottom plate of the amp you can see the cicuit board clearly, allong its edge will be the mosfets (these are the bits make the sound louder in laymans terms) they will be black with 3 silver legs, one end will be screwed to the top of the case. look for any signs of burning or cracks as when they pop they usualy crack or blister, this will also give you chance to see if they have resoldered anything as there will be clean solder not covered with laqure like the rest of the board.
the next wost thing could still be your sub, if you've done damage to it by playing it too loud you may have damaged the voice coil. the only way to check this is with a multi meter set to Ohms, or the Omega sign. check on the alpine site for your model of sub and see what the impedance is, usualy 2Ohm or 4Ohm but some older alpine stuff has diffent impedances. its possible for a 4Ohm sub the get partialy damaged and still work but now be say 3Ohm, this impedance could be too low for your amp and cause it to trip but work fine on a less sensative amp. Last thing i can think of is you've change the bass settings on the headunit or altered the gain on the amp and this is causing it to go into protect mode, simple thing for this is the turn of any bass boost/x=overs on the amp and set the gain to minimum likewise for the headunit, turn off Loud if it's on and turn off and dsp or eq functions and see if this works. Beyond that i really cant think what else it can be. best of luck!