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Car Forum / Driving, Maintenance, Tuning / Car Audio / April 2004Strange voltage drop on remote turn-on wire
Car: 1991 Audi 200 HU: Aiwa cdc mp3 Amp: usacoustics usx4065 After wiring up my new audio system I discovered the amp in the trunk doesn't want to turn on. Tracked it down to the remote turn-on wire which registers 12.2 volts with nothing attached to it, but as soon as I attach my amp to it the voltage drops to 4.5v which is not enough to turn on my amp. Prior to this, I was experiencing intermittant amp power on my old amp which I thought was being caused by the antenna booster which I wired in parallel to the HU remote turn on along with the old amp. Wired in a new amp (that I got for my birthday) and it turned on ok but had horrendous ground loop noise. I figured it was too much resistance in the 24awg wire I was using to run back to the trunk (antennae booster is not connected) which had 3 butt connectors in it and several different wires. But when I replaced it with a single 16awg wire it does the same thing. If I jumper the 12v and remote posts on the amp it does turn on so I think that my 4 year old Aiwa HU is not performing at 100% anymore. Could this be a symptom of poor head unit ground? I plan on using a relay to send 12v from the battery to the amp but have to go look for a spare relay in my parts bin. Hopefully the HU is making enough power to trigger the relay. thanks for looking! Chi It certainly sounds like either the amp is drawing too much current at the remote turn-on input, or the output resistance at the head unit is too high. You've ruled out the wiring, since a 16-awg wire didn't cure it. The only other thing I would suggest would be to measure how much current is being drawn by the remote turn-on input on the amp. It shouldn't be much, certainly less than a 1/2-ampere or so. If it's drawing excessive current, that could cause a voltage drop at the head unit's remote turn-on output. Scott Gardner >Car: 1991 Audi 200 >HU: Aiwa cdc mp3 [quoted text clipped - 29 lines] > >Chi One thing you can do, assuming it's not an amp problem, is use the remote turn on wire to activate a relay (powered by 12V from a beefier circuit, wiper blades maybe) that will then turn on the amp/amps. I use this method to activate 4 amps in my car. You can get a relay at any auto parts store. > It certainly sounds like either the amp is drawing too much current at > the remote turn-on input, or the output resistance at the head unit is [quoted text clipped - 42 lines] > > > >Chi > One thing you can do, assuming it's not an amp problem, is use the remote > turn on wire to activate a relay (powered by 12V from a beefier circuit, > wiper blades maybe) that will then turn on the amp/amps. I use this method > to activate 4 amps in my car. This is assuming the head unit is not at fault. Most relays draw more current from the remote wire than a single amp will. This is why he first needs to identify which component is the problem. >> One thing you can do, assuming it's not an amp problem, is use the remote >> turn on wire to activate a relay (powered by 12V from a beefier circuit, [quoted text clipped - 5 lines] >current from the remote wire than a single amp will. This is why he first >needs to identify which component is the problem. Yep, the standard Bosch-type automotive relay draws anywhere from 90-160mA to activate the relay. If the problem is with his head unit, and the head unit can't turn on an amplifier, it probably won't be able to reliably activate a relay either. Scott Gardner Can someone help me with my current measurement? When I set my cheap digital multimeter to 10Amps I get a reading from the amp's remote turn on of .01 (by touching the 12v post with one end and the remote turn on post with the other end) When I put the meter on the 200m range I get a 13.6 reading. Does this sound like a normal current draw for a remote turn on? thanks in advance! Chi > It certainly sounds like either the amp is drawing too much current at > the remote turn-on input, or the output resistance at the head unit is [quoted text clipped - 8 lines] > > Scott Gardner I don't know what meter you have, but .01 in the 10A mode probably refers to .01A, and 13.6 in the 200m mode refers to 13.6 mA. Since 0.01A = 10mA, the two measurements are in agreement. In other words, if your meter is correct, your amp isn't the culprit here. It's your head unit.  SignatureMark remove "remove" and "spam" to reply > Can someone help me with my current measurement? > [quoted text clipped - 22 lines] > > > > Scott Gardner When you took the measurement, was the turn-on wire disconnected? Checking the current between the +12V post and the remote post is valid, as long as there wasn't anything else connected to the turn-on post at the time. If the head unit's remote lead was still connected to the amp, and the head unit was turned on, the current between the head unit and the amp wouldn't have been detected by the meter. Otherwise, I agree with Mark that 13.6 mA seems like a good reading. In that case, it sounds like something is wrong with the remote turn-on output of the head unit. It probably wouldn't be financially worth it to have the head unit repaired, and if the head unit can't support 13 mA to turn on the amp, it's probably not going to be able to power a relay, either. Perhaps you could connect the turn-on post of the amp to a switched 12V wire. This way, your amp would be powered on whenever your car is running, but at least you could be sure of getting enough voltage to turn on the amp. Scott Gardner >Can someone help me with my current measurement? > [quoted text clipped - 22 lines] >> >> Scott Gardner It's probably not the best idea to power your FM booster from your remote output. Hopefully it didn't damage your deck. As Scott said, measure the current draw by the amp alone (simply connect both leads of a meter to the remote and power terminals of the amp, and make sure the meter is in current mode). It should probably be in the 100mA or less range. If it's significantly more than that, then that could be the source of your trouble. But my guess is that it's the head unit at fault. SignatureMark remove "remove" and "spam" to reply > Car: 1991 Audi 200 > HU: Aiwa cdc mp3 [quoted text clipped - 29 lines] > > Chi |
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