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Amp in Protect Mode - Troubleshooting

Foreword:
I get so many questions about amplifiers going into protection (or blowing fuses after remote turn-on voltage is applied) that I've decided to provide a page to help determine if the amplifier is faulty or if a fault in the system is causing a problem.

Notes:

  • Many amplifiers will illuminate their protect LED during the mute delay (when you initially power up the amplifier). After a short delay (2-10 seconds), the protect LED will go off. For those amplifiers this is normal. Other amplifiers ONLY illuminate the protect LED when there is a problem. If you know how your amplifier behaves when the amp is in good working order, it will make troubleshooting much easier. If you are unsure about this, you can email me or ask someone on a forum where they're familiar with the amplifier you have. For the most part, this page is for amplifiers that go into protect mode and remain in protect mode or go into protect mode when the amplifier is driven hard.
     
  • Many times, the protection indicator will blink to indicate the reason the amp is in protect mode. The owner's manual is the best source to help you decode the blink sequence. This is common on older Alpine amplifiers.
     
  • Not all amps have a protection mode indicator. Some simply shut down and the power light will not illuminate when in protect mode. If the power light blinks then goes off, the amp is either going into protect mode or there is a bad connection in the power supply wiring.
     
  • Generally, the power light is green or blue and the protect light is red but on some amps, the protect light is green and the power light is red. Look at the silkscreen on the amplifier to confirm the function of the LEDs
     
  • Some amplifiers have multiple protect lights. For example, some of the Sony amplifiers have lights for power, overcurrent and thermal protection. The lights are always lit when the amp powers up but are normally green. When there is a fault, the LED changes from green to amber.
     
  • Many amplifiers show protect when initially powered up (mute delay) and then switch to green. Sometimes it's a single LED that changes color (PPI). Sometimes it switches the red LED off and switches the green on (Planet Audio, Power Acoustik and similar amps). Some (like the old Autoteks) light the green LED and red LED initially then the red LED switches off.
     
  • In MANY amplifiers, the power LED will be lit but the amplifier will be completely dead internally. This is especially true when the power supply has failed.
     
  • There are a few amps (some JL Audio) that will go into protect and none of the indicators change. This happens when the voltage drops too low when the amp is being driven hard with an insufficient power supply. Sometimes, a VERY brief drop in voltage (too short to be seen on a standard multimeter) will cause the amp to shut down for a short while.
     

Again... It's helpful to know how the amplifier behaves when working properly. If your amp is working properly, pay attention the way the indicators light up when powering the amp up. If you don't know how they're supposed to behave, ask around.

Step 1

On-board Fuses:
The first thing you need to check is the on-board fuses plugged into the amplifier (if it has them). Not many amplifiers will illuminate the protection light when the fuses are blown but a few will so you need to check this. If the fuse holders are melted, you need to have the amp checked by a technician to determine why they melted and to determine if the fuse holders are usable. Generally, when the fuse holder melts, the contacts become badly oxidized and the clips lose their tempering. This means that they can no longer function properly and will continue to overheat.

For those who don't know what a blown fuse looks like, the one on the left below is blown. The one on the right is OK.

Step 2

B+ and Remote Voltage:
Not all amps have low voltage protection but some do (MTX, Rockford and most of the Japanese brands). This means that you must confirm that you have sufficient voltage reaching the amplifier for it to operate properly.

With your multimeter set to DC volts, the black meter probe on the ground terminal of the amp (not on the point where the ground wire connected to the vehicle) and the head unit on (so the amp will have remote voltage applied), touch the red probe alternately to the B+ (battery +) and remote terminals of the amp. If the voltage is below ~11 volts, you need to check the wiring feeding whichever line is too low. Normally, both will be above 12v. It's important that you leave your head unit on during testing so that the remote line will have voltage on it, the amplifier will be on, and the amplifier will be drawing current. Sometimes the voltage will only drop when current is being drawn from the power source.

If the amp only shuts down when the amplifier tries to produce high power (when it hits a strong note), you need to measure the voltage at the time when the amp shuts down. The voltage drop should be minimal when the amp is producing/trying to produce significant output. If it's dropping below ~11v, you need to determine why.

If you have confirmed that you have sufficient voltage on the amplifier's B+ and remote terminals and have a good ground, procede to step 3.

Important!
Above, I purposely recommend placing the black probe of the meter on the ground terminal of the amp. If you place it on a chassis ground point in the vehicle and there is a bad connection between the amplifier ground terminal and the chassis ground, it will appear that the amplifier has sufficient voltage at the B+ and remote terminals (assuming that the feeds to those are intact).

Bad Ground?
If the voltage at BOTH the B+ and remote terminals is low and your vehicle's battery is not low (check the voltage at the battery with the multimeter), touch the black lead to a known good ground (a point scraped to the metal on the floor pan of the vehicle) and the red lead to the ground terminal of the amp. If you read more than 0.01v and the amp is at idle, you may have a bad ground. If you read over 0.1v, you definitely have a bad ground.

If you find that the B+ or remote voltage is low at the amplifier, you need to trace the voltage back to the source to determine where the voltage is dropping. At each connection, fuse or other point where the wire is not continuous, check the voltage. You need to check the voltage on BOTH sides of each connector and fuse holder. Since the meter leads are not long enough to reach the grounds at the battery or trunk over the long run of the power wire, you need to scratch the paint/primer/undercoat to bare metal at each point where you need to check the voltage. If you find that the voltage is good on one side of a connector or fuse but not on the other side of the connector/fuse, you need to replace the connector or fuse. In some cases, the connections between the wire and the fuse holder will be a problem. You will also see defective fuse holders.

Clues to a Bad Connection:
Generally, when there is a bad connection and the connection has been bad for an extended period of time, the insulating material around the connector will be melted. The image below shows a terminal block that melted because the set screw wasn't tight enough on the wire (this is very common). In this particular amp, the damage was so bad that the block melted the solder and pulled out of the board.

Fuses - Open But Not 'Blown':
Also, just because a fuse doesn't look blown, that doesn't mean it's intact. If there's a question, pull the fuse from the holder and measure the resistance across it (set meter to ohms). The resistance across fuses rated more than a few amps will be essentially 0 ohms. Most meters will not read to 0 ohms. To know how low your meter reads at 0 ohms, touch the leads together for 5 seconds. This is what you should read when you touch the meter across the fuse (out of the fuse holder).

The following demo is from the Installation Primer page of my Basic Car Audio Electronics site. At every point where there is a green indicator, you should check the voltage. Using the demo should help you to better understand where you'd lose voltage when there is a break in the circuit.

Step 3

If the voltage remains near or above 12v but the amp still goes into protect mode, disconnect all speaker wires from the speaker terminals of the amp and disconnect signal cables from the amp. It's important that you disconnect the speaker wires from the speaker terminals of the amplifier and disconnect all RCA cables from the RCA jacks of the amplifier.

If the amp powers up after disconnecting the speaker and signal cables from it, try reconnecting the RCA cables. If the amp goes into protect with the RCA cables plugged in, go to step 4. If it doesn't go into protect, reconnect one pair of speaker wires at a time. If you're using a mono amp and have only one pair of speaker wires, you'll need to disconnect all but one speaker from the other end of the speaker wires. If you find that one pair of speaker wires or one speaker causes the amp to go into protect, disconnect all speakers from the other end of the wires and separate the wires so they can't touch. If the amp still goes into protect, you have a bad speaker wire or the wire is shorted to chassis ground. If the amp only goes into protect when one particular speaker is connected to the amp, you have a defective speaker. .

Step 4

If the amplifier goes into protect with the RCAs plugged in (but all speaker wires disconnected), there could be several problems. You first need to check the RCA shields of the head unit. THIS link takes you to a page where it's explained in detail. If the shield ground of the head unit is OK, the amplifier could have one of several problems. You need to power up the amplifier and measure the voltage on the shields (shiny outer metal ring) of the RCA jacks. Touch the black meter probe to the ground terminal of the amp and the red meter probe to each of the RCA shields. If you read 10v or more, the amplifier may have a shorted transformer. If you read something less than 1v, the transformer is likely OK.

Some amplifiers have a problem with broken connections between the RCA shield and the circuit board. This is sometimes difficult to check unless you know how the input circuitry of the amplifier is designed. In most of the budget amplifiers, the shield will be directly connected to the NON-bridging speaker terminals. If you have that connection, the shield ground connection is intact. Sometimes, the connection is intermittent so you need to move the RCAs while you're checking to insure that the connection is solid.

Shorted Output Transistors

If the amp goes into protect with no RCA or speaker cables connected to it or if the amplifier blows the fuse AFTER remote voltage is applied, the amplifier likely has shorted output transistors. If that's the case, the amplifier will need to be repaired. If you'd like to repair it yourself, read the Amplifier Repair Primer page. It will help you troubleshoot many amps down to the component level.


 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

If you find a problem with this page or feel that some part of it needs clarification, E-mail me.

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