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Repair amp don't want to power on

I blew my amp last week. (short circuit on the output speaker :S) I see that the four 75339P were smoke. I changed all four with IRF3205 and now the amp doesn't want to turn on. (no sound and led doesn't power on) Do you have an idea if I have something else blew? I have also test DC voltage on each of the 16 pins of the TL494 when power is on. Here's the DC voltage of the TL494 PIN #1 : 0 PIN #2 : 0 PIN #3 : 0.06v PIN #4 : 1.15v PIN #5 : 0 PIN #6 : 0 PIN #7 : 0 PIN #8 : 11.5v PIN #9 : 0 PIN #10 : 0 PIN #11 : 11.5v PIN #12 : 11.6v PIN #13 : 5v PIN #14 : 5v PIN #15 : 5v PIN #16 : 0 I don't what to do now. Thanks for your help! Dominique

Posted by Dominique Landry on


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  • 113 Answers

SOURCE: my 7801 doesnt turn on

check pwm circuit amps turn on with 3-4 volts on mosfet gates ic 494, 5252or 555 controll these.hit me up for more

Posted on Aug 09, 2007



  • 631 Answers

SOURCE: mtx81000d 3rd chance

The original output transistors (SSP45N20A - if I'm not mistaken) for this amplifier are very difficult to find and there are virtually no substitutes that will work without extensive modification. Many techs try to use the SSP45N20B but they don't work reliably.

If you do find replacements, expect to pay $15 or more each. It's possible that there are other problems also. For example, the over-current protection may not be working properly. When it's working properly, it will generally trip when the output transistors fail (which prevents damage to the subs).

This is an old design. The newer amps will be more reliable and will generally offer better protection for the speakers.

Posted on Nov 19, 2007



  • 47 Answers

SOURCE: here it goes the amp powers on and seems ok

Sorry to say mate but that is one blown up amp! :(

My solution to this would be to get another amp

Sorry Matey

Upfront Audio

Posted on Apr 23, 2009


  • 19 Answers

SOURCE: No sound from speakers, but there is power to amp

make sure the power wire and the remote wire have voltage. at least 12 volts. make sure the ground wire is good and has a good solid ground. after that make sure the rca cables are getting signal from the radio. if you have a small speaker or tweeter you can touch the wires from the speaker to the rca cables and it should play music very quietly. meter the subs and make sure theyre ok and not shorted or bad. if all that checks out good.... the amp is probably bad. start with all the simple stuff and work youre way up. if the amp has good power and signal and good speakers then the only thing thats left is the amp. good luck

Posted on Dec 30, 2009


  • 64 Answers

SOURCE: My MTX JH600 works intermittently.

One of my friends had a amp like that , i looked at it an the inside of speaker box wires was touching , if thats not it then check ur power an ground , power wire must be the same size ground an if ur ground is not grounded good then u will get the cuting out .

Posted on Jun 11, 2011

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Having trouble with all my speakers except my twitters in a 2007 Saturn Outlook...what do I start with? Fuses are good

Speakers get power from the amp if your system has one or from the radio , if the tweeters work it's not a fuse problem . You like listen to your stereo loud . Blew a channel in the radio or amp ?
Take it and have it checked for DTC'S - diagnostic trouble codes
DTC B1025 01: Audio Output 1 Left Front Circuit Short to Battery
DTC B1025 02: Audio Output 1 Left Front Circuit Short to Ground
DTC B1035 01: Audio Output 2 Right Front Circuit Short to Battery
DTC B1035 02: Audio Output 2 Right Front Circuit Short to Ground
DTC B1045 01: Audio Output 3 Left Rear Circuit Short to Battery
DTC B1045 02: Audio Output 3 Left Rear Circuit Short to Ground
DTC B1055 01: Audio Output 4 Right Rear Circuit Short to Battery
DTC B1055 02: Audio Output 4 Right Rear Circuit Short to Ground

Each of the audio output channel circuits (+) and (-), at the radio and audio amplifier (if equipped) have a DC bias voltage that is one half of the battery voltage. When using a DMM, each of the audio output channel circuits will measure approximately 6.5 V DC. The audio being played on the system is produced by a varying AC voltage that is centered around the DC bias voltage on the same circuit. The AC voltage is what causes the speaker cone to move and produce sound. This voltage will vary depending on what type of audio is being listened to, talk or music, and type of music, as well as the volume setting of the system. Low volume and talk settings will measure around 1V AC and less, where constant music may measure 3 V AC and slightly higher.
Do you know how to do DC voltage testing ?
Without Amplifier without UK6
Ignition OFF, disconnect the harness connector at the appropriate speaker.
Radio ON, test for 5.0-7.5 V between the signal circuit terminal A and ground.
? If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the radio.
? If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the radio.
Test for 5.0-7.5 V between the signal circuit terminal B and ground.
? If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the radio.
? If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the radio.
If all circuits test normal, replace the speaker.

Dec 25, 2016 | Saturn Outlook Cars & Trucks

1 Answer

My GFA 555II amp blew the 2 left channel fuses while playing at normal loudness levels.

Fuses blow when there is a short circuit. All you need to do is replace the main output devices located on the heat sink. They are the ones that will have shorted most likely. Check your speakers and wiring for that channel. Any wire cross connecting will cause that kind of fault, likewise a faulty speaker.
Any engineer will be able to do this job, providing they can find the parts. But you can check them yourself by looking for the parts on the internet.

Mar 03, 2016 | Audio Players & Recorders

1 Answer

I have a Pioneer VSX-305 receiver. I blew channel A speaker outputs by allowing speaker wires to touch. Everything else works. Can anyone tell me what it takes to fix this. (I am an electrical engineer...

Without a Sams Photofact or a service manual I would go directly to the Power IC which is the largest Integrated Circuit mounted to a large heat sink. If you see any fuses they are probably for the power supply since any fused circuit on the speaker output would be ineffective because the IC would be damaged before the fuse would blow, but you need to check them anyway. Since the short was at the speaker output your problem should be at the final stage of amplification, which is the Power Amp IC. Prior to the early 70's you would have transistors mounted to a heat sink which could be individually checked and replaced. Then manufactures started to use the Power Amp IC which are more costly but eliminate having to find matched pair transistors. All you can check on the Power Amp IC is if you have an input using an oscilloscope or signal tracer and the power to the IC. If you have an input signal and power to the device with no output, I would replace the IC. Unless you have a test circuit for the IC you cannot test it completely unless you have a device like a Huntron Tracker or build a test circuit using a signal generator and a power supply to measure the gain of the IC with an oscilloscope. Short of ordering a service manual this is a good place to start.

Aug 15, 2011 | Audio Players & Recorders

1 Answer

Have a Crown amp xs 1200 that is in fault mode and wont reset what can i do to fix this

You may have two speaker wires touching eachother (shorted) or one of your speakers may have a fault and not giving enough resistance to the amp (shorted).
Last option is that one power output transistor is damaged and appears to be a short circuit to the circuit protection system.

Jun 22, 2011 | Crown XS1200 Amplifier

1 Answer

Short circuited rear left speaker cable which seems to have killed that output. Don't they have short circuit protection on MOSFET amps?

Even with the protection the outputs will blow if the "short" was not complete.
The heat will build up and waste the driver. Almost shorted will do this almost always.
There may be an internal fuse that blew. Ask a shop if that model is fuse protected.

Jan 23, 2011 | Pioneer Car Audio & Video

1 Answer

Fuse blew and replaced, now sounds bad, what happened?

Fuse is blown because you may have bad DC to DC converter circuit (step up circuit from 12vdc to provide +-/- 30~40vdc) that supplys the power amp section. I can be that the output stage of the amp shorted out and it took out the DC to DC converter circuit.

Oct 31, 2009 | Infinity BassLink II Car Subwoofer

1 Answer

While playing a CD, my Nakamichi Receiver 2 made a ''pop'' noise and lost the signal, with some smoke coming from the top vent near the front. It was in a confined area, and I believe it overheated and...

The output section has a problem. The receiver is in "protect" mode and wioll not turn on the speakers. This unit needs service. In all likelyhood, one or more of the output transistors has shorted and hte smoke came from a resistor that fried. This is a relatively simple repair for an audio repair shop. Figure around $40 for parts for this repair.


Oct 05, 2009 | Nakamichi Audio Players & Recorders

1 Answer

Low output from amp

From a former DJ, make sure that the speaker circuit is matching the load that is required by what ever amp that you are using. If the amp is rated at 1000watts/ channel into 8 ohm's then your equivalent speaker circuit has to match. I repeat has to match! If it does not the amp will either short out or be overloaded. If you are using all 8 ohm speakers on a amp that rate its output at 1000 watt/8ohms then you you have to match the watts and the ohms. Depending on how much power your speakers take you may have to use more than one speaker to handle the power. If you have to use more than one speaker you will have to use a series/parallel circuit to keep the ohms at 8ohm. You have to use ohms law for adding resistor in series and paralell. If more is needed please reply.

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2 Answers

RCA 5-CD Shelf System, RS2654 Fuses

Never ever replace a fuse with a bigger one, you are lucky the unit did not blow up and statrt a fire. When a fuse blows there is usually a reason.There is a short in the main power supply or the output stage. You will need to test for shorts on the main transformer, B+ rectifiers and the main filter capacitors. If that does not show any shorts, you will need to test the audio output circuits for shorts on the audio output IC's. Good Luck

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