Impossible problem?

Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=25863
Printed Date: April 19, 2024 at 9:19 AM

Topic: Impossible problem?

Posted By: Simplemitch
Subject: Impossible problem?
Date Posted: February 04, 2004 at 8:24 PM

I've got a customer vehicle (96 grand-am) that came in today for a troubleshoot for no audio from subwoofers. So i checked the subs...they're OK. I benchtested the amp... it's OK then i hooked up a CD walkman as an alternative signal source and Ta-da! the subs fire up. Ok, so its RCA's forward.... RCA's test ok, so i benchtest the head unit and the pre-outs work fine.... He had tried to install the unit himself and he blew out the car's 12+ constant (seen it a million times before...) so his "buddy" t-tapped onto the ignition column wires to achieve a 12 +, a switched 12, and a ground (to the dash subframe) which worked, but i redid all of this to alleviate any possibility that poor connections could cause such a bizarre problem, but Lo! no fix. SOOOO.... how can a good head unit, good rca's, a good amp, and good subs produce no output? (especially when the subs work when hooked to an external signal?!?) .............Anybody?.............

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Mitchell Whitney, Installer/technician
Mainstreet A/V

Replies:

Posted By: RufNUSD
Date Posted: February 04, 2004 at 8:33 PM

remote wire? which deck outputs did you test? are the testing circumstances the same for both units?

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Someone pass me that bottle.

Posted By: Simplemitch
Date Posted: February 04, 2004 at 8:47 PM

its not the remote. the amp turns on, it just acts as though its not getting a signal from the headunit. i tried two different headunits in the vehicle (both his. one sony and one JVC). on the bench ALL preouts ( on both units ) test fine. and with the radio on in the vehicle, if you unhook the Headunit from the amp and replace it witch an external source (such as a CD walkman) the amp and subs operate fine. its the damn weirdest thing i've seen in 8 years.

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Mitchell Whitney, Installer/technician
Mainstreet A/V

Posted By: Alpine Guy
Date Posted: February 04, 2004 at 9:47 PM

maybe the the rca's aren't passing enough current. Did you try new rca's from the deck to the amp?? sounds like the only thing you haven't tryed. Low level rca signals are so low in current its hard to determine if rca's are good by useing a walkman like you said. Try that and hope for the best.

Posted By: Simplemitch
Date Posted: February 04, 2004 at 9:51 PM

Already did it. with the head wired in but removed from the dash i just hooked up a new set of RCA's between the head and the amp with the same result. Messed up, huh?

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Mitchell Whitney, Installer/technician
Mainstreet A/V

Posted By: MAXST
Date Posted: February 04, 2004 at 10:29 PM

what about loose connections on the amp..and it sometimes works?

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I need quality equipment, feel free to donate.

Posted By: Simplemitch
Date Posted: February 04, 2004 at 11:18 PM

Nope. Eliminated that chance earlier. This is actually day 2 of this ordeal. On Tuesday he came in and said his subs "werent hitting as hard as they used to". he had installed the whole system himself and it showed. First up, he had 4 holes (not ports, just holes) on the enclosure....Anyway, The amp was lit but i could see that the ground wire was just wrapped and TAPED to a chasis bolt and sure enough a gentle tug and away it came. Also he had 4ga up to within 4 inches of the amp and then a distribution block with 8ga the rest of the way to the amp. Circuit City told him to do that one.... So after redoing the ground and putting a proper terminal on the 4ga primary, and also putting a female disconnect on the remote wire (its a Rockford Fosgate with the male spade for turn on, which he had wrapped the wire through...), then adjusting the gain (it was completely minimized which is a first) everything was Operational and away he went. So today begins day 2. He came in and said that the setup worked all day Tuesday, but today when he started his car he said " the subs just wouldnt work". and then from there is where this post topic starts. Anybody got ideas? xx(

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Mitchell Whitney, Installer/technician
Mainstreet A/V

Posted By: jacksonj
Date Posted: February 04, 2004 at 11:21 PM

I'm definately not an expert, but the only thing I can think of is maybe the HU has a Sub control in the menus that may be turned off, or just very very low.

Posted By: Simplemitch
Date Posted: February 04, 2004 at 11:43 PM

nope. tried all outputs, checked all menus, plus they work fine on the bench. Good thought, though.

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Mitchell Whitney, Installer/technician
Mainstreet A/V

Posted By: BaddestBanshee
Date Posted: February 04, 2004 at 11:58 PM

put in a test tone cd and check rca voltage at the deck, then the rca ends at the amp. Or run an external set of rca's to the amp from the head unit. Its all about basics, if you are thorough, you will find the problem.

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Want to know about Audi, I thought you did.

Posted By: jacksonj
Date Posted: February 05, 2004 at 12:02 AM

When you say the parts tested ok on the bench, I'm sure you're referring to each one separtely. Why not try to hook everything up together outside the car. Maybe then it may be easier to see the issue and also easier to switch a unit out to test with.

I would test that his HU works with Another amp and sub, and that other HU you had mentioned is able to work with his amp and sub, just to eliminate it further, these are methods I take when fixing computers or my own car audio problems.

Other then that, good luck.

Posted By: Simplemitch
Date Posted: February 05, 2004 at 12:16 AM

i like these last two ideas. i'll do a comparative check of the output signal using o scope once on the bench then once in the car and if prob is not found, ill hook the whole system up on the bench. That ought to discover something. Thanks guys, and if anyone else has some good ideas, dont hold back, i'll take anything.

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Mitchell Whitney, Installer/technician
Mainstreet A/V

Posted By: SDmustang21
Date Posted: February 05, 2004 at 2:12 AM

i had a similar problem which might help. I have a dvc rockford fosgate and would notice that sometimes it lost power. turned out to be a sort of cut rca which would work when it was jiggled. that in turn would either cut half the signal going to the sub or give it it's full potential. Now that i have my whole system out of my car i also noticed that it had a gash in the middle of the run, probably from running it across something sharp. sound's to me like this might be it..could also be the rca's aren't making contact at the amp or head unit ( loose fit).

I found out that a bad connection to either right or left channel will seriously lower the sound level of a speaker which is bridged from an amp into dvc woofer.

egghh....just something to think about...don't know what kind of woofer he's running

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Buy it, install it, play with it. Then take it back out, read the instructions, install it better!

Posted By: Simplemitch
Date Posted: February 05, 2004 at 8:55 AM

yeah, i tried new rca cords to no avail. his are also definately ok. I think you guys are starting to see why i named this thread "The Impossible Problem" . How can operational components become un-operational when hooked to each other? I'm gonna have him come in today and try the whole thing on a bench. That will at least determine whether the problem is car related or equipment related.

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Mitchell Whitney, Installer/technician
Mainstreet A/V

Posted By: DYohn
Date Posted: February 05, 2004 at 10:29 AM

RCA problems was my first inclination too. Hmm. Could be that the amp has bad input pre-amplifiers, or it was damaged by the sh*tty original install. The HU could be shutting down due to a low impedence load on its line-outs. Try swapping in another amp to test this.

Posted By: dcgc
Date Posted: February 05, 2004 at 1:01 PM

I had a problem with my CD not working.

I had used the remote antenna for the remote turn on.

FM worked(as far as sound coming thru), but the CD didn't turn on the amp.

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2003 Silverado Ext. cab
Kenwood mp922
Kenwood kgc6042a EQ
JL Audio xr650-csi
MB Quart PSC 213
JL Audio 300/4
pair of JL Audio 12w6v2
JL Audio 1000/1

Posted By: forbidden
Date Posted: February 05, 2004 at 1:16 PM

Chances are that you have the blue wire confused with a blue / white wire. One wire gives +12 volts when the radio is activated and is open with the cd player operating, the other wire gives +12v when either radio, cd or aux input is used. Check to see if these wires are both present, chances are that this is your mystery problem.

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Top Secret, I can tell you but then my wife will kill me.

Posted By: Simplemitch
Date Posted: February 05, 2004 at 4:00 PM

Forbideen, were you talking to dcgc? cuz thats definately his problem. i've seen alot of people do that with kenwood decks. If you were talking to me, then no, thats not it, cuz the amp doesnt shut off, it just puts out no signal. I'm having him come in tomorrow so i can set it up on the bench.

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Mitchell Whitney, Installer/technician
Mainstreet A/V

Posted By: Simplemitch
Date Posted: February 05, 2004 at 4:02 PM

Posted By: mecpcert_1
Date Posted: February 06, 2004 at 5:21 AM

how many subs are hooked up? are they svc or dvc? when everything works, how long does it play for? i had a problem with a svc woofer before, it would play when it wanted to. hit a bump and it would come back on. when it stopped playing, if i pushed in on the cone, it would play again. after using my ohmeter, found out it was the tinsel leads between the terminals of the woofer and the cone itself. re-soldered to no avail, it eventually stopped working altogether.

i would also try metering the ac signal rca output from the deck @ the deck. next, meter the same signal @ the rca before the amp. try also continuity test of the rcas.

you mentioned that the amp was rockford. does it have a bass knob? if so, check the connection. rf amps will lose 3db without it hooked up.

do the highs work? 4x6's and 6x9's. most decks shut down the internal amp if a single speaker is shorted to ground or shorted period. if so, that may hinder your signal output to the sub amp. there is only one amp, right? no external x-overs in there? it would help better if there were more specifics about the equipment involved.

those are just my thoughts...............good luck!!! posted_image

p.s. just curious as to the solution of your ordeal, please let us know what you find.

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do it right the first time....less warranty work=more money!:)

Posted By: EzekialPhoenix
Date Posted: February 06, 2004 at 11:33 AM

Set the car on fire, then push it over a cliff. Start over.

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I be tossin and flossin, my style is awesome. Causin' more family feuds than Richard Dawson.

Posted By: thapimpfromchi
Date Posted: February 06, 2004 at 12:00 PM

Hey man, does he have one rca running from the radio using a splitter? or is it 2 wires? Um... are his power wire and his RCA's run together? it might be picking up noise from something else and not giving the amp a good enough signal. there were too many posts onhere to remember which was which, but did you say you tried another set of rca's? and got nothing?

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1990 Honda Civic HB:
Clarion DXZ545MP H.U.
2- 6.5" Power Acoustik interiors
Diamond Audio 600.1 amp
Diamond Audio 15" M6MKII
Pyramid PB881X 4 CH. Amp