Question about Infinity Reference 7541a Car Audio Amplifier

2 Answers

Infinity 7541a Amp

You sent me a request to clarify what is going on with my amp. Anyway I read your page and we have alot in common. I am also ASE certified or should I say was, never renewed. Also I am an electronic tech, I graduated from Tampa Tech which is now called ITT Tech in Tampa Florida back in 1996. Alot has changed but basic electronics is still basic electronics. I want to thank you for replying to my post. First I am having the same problem as another person with the same amp, power and clipping light flashing back and forth. Manual says amp needs to be serviced when it does that. So basicly most of the time the final output transistors are fried or power mosfets are fried, either or. I was seeing if anybody found a solution to this problem yet. I have'nt had much experience in repairing car amps except for replacing some output transistors in a couple of friends' amps that were fried, you could actually see them blown apart so I knew right off that was the problem plus he was running it at 1ohm bridged on a 4ohm bridged amp. Well to begin I was doing a few tests of my own just basic voltage and ohms tests and was trying to ask if you can aproach a car amp just like any other audio amplifire. Say like a home stereo. I used to have a electronic repair shop in a small town here in Florida. I only had a couple of car amps come in so like I said have'nt had much experience in car amp repair. I do have the service manual that some guy I asked to send to me and he did, so at least I have that. Now I also found a site your probably familiar with called bcae1.com Basic Car Audio Electronics. It is a very good site for the novice person wanting to fix thier amps. Gives very detailed info on repair. The guy wants you to buy his DVD rom for $49.95 and I believe it's worth it. Anyway back on the subject brother, I was saying I took some basic voltage and ohms ratings on the output transistors but did'nt know what ratings I was looking for. Even though I know electronics A person can allways continue to learn and it's been 8 or 9 years since I've had my shop and need to brush up and start remembering my tech training, know what I mean. I still know my auto mechanic skills cause I use them still, alot on friends cars as well as people I just happen to run into. So If you can help me or know anything about this paticular amp, it would be greatly appriciated. I can send you the service manual and some pics of the insides if it would help you help me. That site I told you about has been helping out alot but like I said you might know something else thats usefull. So get ahold of me or if you want I would rather call you and talk in person if you don't mind so let me know. I think you can find my e-mail when you click on my name. Well, thanks my brother and hope to speak to ya soon. Later on Bro

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  • Mark Skinner Jan 17, 2009

    To rah1379: No I have not had a chance to check the output transistors yet. I am thinking thats what is is since it's very common other than the power mosfets. I am goining to take them off the board to test and I will let you know. Thanks for the hel and please continue to stick with me thru this. As I am an electronic tech, it's just been awhile since I've messed with electronics but have'nt forgot alot of things. I went to a tech school in Tampa Florida for electronics just trying to get refreshed. Thanks for the help. When I hook up amp all I get is protect light and clipping light going back and forth so in the manual it says it needs to be serviced so thats where I'm at. All hellp welcome. Thanks

  • Mark Skinner Jan 18, 2009

    To rah 1379, Thanks for the info I will try those tests and let you know. In the mean time after that could you please continue to help me thru this after I have done tests and checked output transistors? If so thank you very much. Also I have a Insignia

    NS-p2000 that I just got last week. When I hooked power up and had the bottom cover off, I heard like an arching noise near the torroidal transformer on one side or it was coming from the power mosfets/transisors. It did'nt go into protection mode also, it just kept making the arching sound. Then finally it quit and I have'nt tried it again. The fan powerd up each time and the light stayed green, so I have no idea yet, that ones next. Also took board out of amp and everything looked fine, no burnt marks or bad burnt smell. Anyway like I said that ones next. Thanks very much rah1379

  • Mark Skinner Feb 12, 2009

    Hi, I finally fixed my amp a couple a weeks ago. Turns out the amp had 2 shorted output transistors, TIP35c & TIP36c. I ordered transistors along with some others for 3 more amps I was repairing and put the new ones in, fired up the amp and she works fine. For some reason though, the power light does'nt come on and it's not blown out. Also on the front channels only, if you switch the crossover mode switch to lowpass the sound cuts in and out and a lot of current gets sent to the speakers. I watched the speakers go in and out when I moved switch. In fullpass mode amp works fine, only happens on the front channels. Anyone else have this problem? I know one person and I can't remember where I found it.

  • Mark Skinner Feb 12, 2009

    Hello pbabin could you send me your e-mal address, I've seen it on a couple people you helped out and should of written it down but if I had it I could write you easier to explain. Thanks. Like I said, Only on the front channels 1&2 move thxover switch to lowpass and a bad flucuation in the speakers and the sound cuts out. Need to find out what's causing this cause it's the only proble left. Works great on fullpass though, weird. I'l check volts at the opamp on each pin and see what turns up. I;m thinking it could be a capacitor, maybe.

  • Mark Skinner Feb 13, 2009

    Hello pbabin I got your request to clarify. Anyway I ended up finding 2 shorted output transistors. I replaced them just for a test with some from a nother amp. All the character numbers matched except for the dissipation wattage. The ones I replace are rated at 80 watts whenn I need 125watts transistors. It was just a test to make sure amp worked after that and it did fine except for that large amount of oscillation when moving the crossover mode switch to lowpass or highpass. Since the transistors are the wrong ones I can almost guarantee those 2 transistors are the problem. Just waiting for the new ones to come. That will probably fix that fluctuation. Thanks for the help, I will let you know what happens when I replace them.. Have a good one amigo.

  • Mark Skinner Feb 13, 2009

    Also once I switch out output transistors I will move on to the crossover switch if problem continues after replacement.

    Thanks for the help. Makes it easier on me.

  • Perry Babin May 11, 2010
  • Perry Babin May 11, 2010

    If the audio op-amps operate from a split supply (±15v), the output of the op-amps should be at 0v DC. Check each output pin. If one output has significant DC on it's output terminals, that could be causing the pulsing when the switch position is changed. I've seen it cause DC offset on the outputs when the switch was set to full range or low pass. If your amp is AC coupled beyond the op-amps, it would only cause a pulse, not offset.

  • Perry Babin May 11, 2010

    Have you tested the output transistor to confirm that none are shorted?



    If so and none are shorted, does the amp produce any sound (poping, audio...) when speakers are connected?

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Who ever is having the problem with the crossovers i have the same problem here altho i have found out the cause ...

my amp was mounted upside down and started playing up if i moved the xover switch the speaker would almost pop out of its voicecoil there was that much current being sent to the speaker

after few mins of looking over the amp there is a bord that slides out of the amps mobo (inside) has the xover switches after 20 mins of fiddling i got some glue set the xover to the pass i would like and glued the xrossover switch still now it works like a charm.. took quiet a bit of playing around with the amp on and moving xover swiches till you find the sweet spot ofcorse you could just replace the xoverbord if you dont want to glue your amp

anyquestions feel free to email me
muffman001@msn . com

Posted on Nov 16, 2009

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  • 120 Answers

Check the speaker terminals for dc, it should be very low,about 100 mV or less, it it is higher you need to find the pots that adjust dc offset to get it down.Also you can compare voltages with the opposite channel to find abnormalities.

Posted on Jan 16, 2009

  • rah1379 Feb 12, 2009

    i would check the switch with an ohm meter, and the circuits it switches in when the problem occurs,check the solder joints and traces as well as the components. The repair disc you mention is a very good one, worth the money if you work on car amps. I bought it about a year ago but dont really work on car amps very often.And yes a car amp is just like other audio amps to troubleshoot, the main difference is in the power level it works with and the power supply is external to it.which model amp was it you are working on?

  • rah1379 Feb 12, 2009

    although the power supply is external on car amps they still have dc to dc converters to boost the 12vdc up to levels needed for the output stages, i just thought of this after i signed off from my last post.

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1 Answer

I have a Infinity7541a amp. I have 7.5 volts dc to the amp. If I disconnect the power to the amp and read it its 12.2. Is something pulling it down in the amp


no. its kinda like a house plug. think of the one on your laptop, on the plug it tells you it needs 240v to power. but it only puts out 12v to power your laptop. the exact same thing is happening with your amp. the amp only needs 7.5 to work but its taking 12.2 to power it. its normal and nothing to worry over

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no for one its a 4 channel amp made for highs mids etc.

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1 Answer

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1 Answer

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Overload maybe. If the amp is run at an improper impedence, the amp will shut down. If you are "CLIPPING" speakers / subwoofers the light will blink to indicate a hard clip . Example: 4ohm/2ohm stable amp with 4 ohm subs wired at 1 ohm.

Jan 28, 2009 | Infinity Reference 7541a Car Audio...

1 Answer

Infinity Reference 7541a protect & Clip lights come on


Hello pianopeter, I have the same amp with the same problem but only when the crossover mode switch on the front channel is set to low pass or high pass. Have'nt fixed that yet cause when I got the amp and put power to it the clip and protect lights would flash back and forth. I turned out to have 2 bad output transistors on the right front channel, I replaced them and amp works great now. Then when I was doing final testing I switched the crossover mode switch to lowpass and your problem occured. I do believe the problem is in the removable board which controls the controls the crossover and input to a point. Try moving the crossover mode switch to flat on both front and rear and let me know if amp works fine that way. I'll be working on this problem soon but would like to know if your problem changes if you move the switch to flat. Please leave me a message as soon as you find out cause this will aid in the process of me fixing problem. I am an electronics tech and buy and fix broken amps all the time so I have a really good knowledge of car amp repair. Once again let me know ASAP, Thanks

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1 Answer

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Does it do the same thing if you remove the RCA input and disconnect the wires from the speaker terminals of the amp?


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1 Answer

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2 Answers

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You would do best with a 12volt inverter. It will bring the house voltage down to the necessary 12 volts for your car stereo. Best of Luck.

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2 Answers

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1 Answer

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