Question about MTX Thunder 1501D Car Audio Amplifier

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Mta 1501d my mtx1501d put out dc at the speakers i replace the caps and transistors but still has the same problem. I opened the amp and tested the resistors at 245,246,247,249 and get a straight beep on the tester and the other gives me a clear reading. any ideas on what happen, can some test thoses resistors and tell me if the should be a reading or a straight beep on the continuity tester. i call mtx and they dont fix that model any more the guy told me its a 4.75 1/10 watts at 1% R245,246,247,249.So can ayone help; me with this.

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You need to switch your meter to ohms and measure the resistance across them. You should read something near 4.75 ohms.

4.75 ohms would cause a constant tone on diode check or continuity.

Did you replace all 8 output transistors?

If not, are you sure that the other 4 transistors haven't failed?

Posted on Apr 17, 2008

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My amp blew one filter cap and some transistors and some mosfets.I replaced all 8 filter caps and transistors and the mosfets,but the protection led stays on. Where else do you think I can check? Your


You have what's known as DC Offset(a bad amplifier) you will need to check the drivers and all the fuse type resistors that are open. You need to check the rail voltages, both positive and negative, at the amplifier. You can't "shotgun" parts. You will need to check them. Be sure to reset the amp to factory defaults, but I doubt that it will help in your instance.This will be a tough repair if you're not an Audio Technician. You will need a Variac as well. For more information, or to inquire about a repair, please visit my website at audioserviceclinic.com. Thank you.

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Sounds like you have a bad amp IC or transistors.
When these go bad they almost always put roughly 40 volts dc from the amp power supply to the speaker terminals. The protection circuit senses this dangerous (to your speakers) dc voltage and disconnects the speaker terminals from the amp via internal relays (the ones you hear click) and puts it into protect mode. If it didn't the dc voltage would quickly toast the voice coils of the connected speaker.

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I have a klh subwoofer about 6 yrs old.it keeps blowing the fuse when powered up. can you help


Okay sounds like there is Fault in the power supply or the output transistor have shorted and is pumping the driver with DC....remove the driver and test with a muti-meter and using the 200 Ohm setting. put it across the terminals of the subwoofer make sure it is disconnected from the amp module....if it is a 8 ohm driver you may get somewhere from 4-8 ohm reading if its a 4 ohm somewhere from 3-6 ohms....if you are getting a 0 ohm or "short" or a really high or infinity "open" reading then the driver probably has caused damaged to the output transistors in the amplifier module. connect the muti-meter to to the red a black leads from the amp module that was going to the speaker...put the muti-meter on the highest possible DC voltage setting Mine goes to 1000VDC and power up the sub amp module now you may get a jump and power up but then it will drop to around 1.0v (or less) that is normal but if it stays high like anywhere from 30-150 VDC then you have blown output transistors (remember if you dont have this issue just skip forward!)...if this is the case pull out the amp module (remember to follow warnings and disconnect from mains power) now the DC filter caps in the module stay charged for long time after power is removed remember: test before touching!! now hopefuly all transistors are laid out infront and you wont have to dig for them the're normally are mounted flat and bolted to a external heatsink on the back. test between all junctions of the transistors B+E C+E C+B make sure there are no shorts...if there is a short replace the transistor. across from it there is its partner...replace him to! more than likely he's faulty because they work in whats called a Complimentary pair...the PNP pulls up the postive and the NPN pulls up the negative..together making a full audio signal. now after replacing all the faulty transistors test for DC on output leads. If there is none carefully connect a NEW driver of the same impendance as the old one.....but do not connect up the old one because you will blow the amp again....now power up and test for sound....all good????


Now if there is NO DC leaking on the Output leads but its still blows fuses there is a power supply fault! pull out the amp module now there is two types of power supply that this sub (or any amp for that matter) uses Switchmode Power supply (SMPS) or the normal transformer supply.im hoping for your sake it is a normal transformer supply it makes it soo much easier to fix....now be very careful you need to check the DC filter capacitors for shorting or any other issues! so undo the board from whatever it is mounted on, now remeber these capcitors can stay charged for along time so be sure to test before touching...if they are still charged and you want to dischrge them i use a 100W bulb (not an energy effiecnt bulb...but a Normal filament globe ) and connect up two leads to it...now put it across the capcitor banks...it will glow brightly and it will slowly dimm....power discharged!!
remeber to check that all caps are fully discharged!!
now test with muti-meter again on ohms mode and check for any shorts...now as you test the resistance will get greater as the caps charge up...this means all is good but if the meter stays at short then you have an issue with one of the filter caps (now if there is a short the caps will not have charge in them but still test!!) Now carefully remove each cap and test to finally locate the shorted one(s)...if there is no fault in Filter caps i would check the power transformer on the primarys so disconnect the leads from the power input socket (remembering the whole time we're doing this power is disconnected!!) and check with ohms meter there could be fault in which case you need to get a new transformer..if its not a faulty transformer.. i would be checking all mains power connections: the switch,interconnection leads,the fuse holder ect...to make sure there is no shorts...now if the power supply is a switchmode supply i would not even go there! i can repair them but it is way to hard to describe here and is not suggested for a DIY'er to attempt to repair but if its 6 years old it should be the way i have described above (normal transformer supply)......feel free to contact me if you need some more help in repairing this..E: ben@xdcpro.com.au
Depending where you are in the world most of the parts for amps can be sourced at local electronic stores or you could ask local repair stores to order parts in for you..if you are in Australia..if you want you can send me the numbers on the parts i can arrange them for you and post them out to you! good luck and i hope this can fix it,ben

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1 Answer

I have a mtx thunder 1501d..i have the power cord connected from the battery, to a power cap and then to the amp...i have the ground connected to the metal frame of the car, to a power cap and then to the...


Hello tonytone54, The ground should go directly to the vehicle frame, never through a cap, fuse, or anything else. Also, if you are connecting positive through a cap, make sure that you charge the cap before connecting it. Hope this helps.

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1 Answer

Noisy left hand power output stage. Noisy transistor? No circuit diagram.


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2 Answers

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To get the clamps off click HERE.

There may be several bad components. Normally, shorted outputs (the most likely cause of DC on the outputs) causes the amp to go into protect mode. In your amp, you may have shorted output transistors, open emitter resistors and possibly a problem with the protection circuit.

To get up to speed on the basics, read through the following page:

Amplifier Repair Primer

After you read through that page, remove the clamps and check all of the output transistors to determine if any are shorted.

Let me know what you find.

Oct 04, 2008 | Power Acoustik GOTHIC OV2-520 Car Audio...

1 Answer

MTX 1501 SCHEMATIC DIAGRAM


MTX never released any of their schematics.

What sort of problem are you having with it?

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2 Answers

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There are a lot of problems that can cause the amp to apply DC to the speaker terminals.

Before we go any farther, you should know that this amp stores enough energy to kill. When power is applied, the transistors must be clamped to the sink. After removing power, you MUST wait for ALL LEDs to go COMPLETELY out.

You need to CAREFULLY measure the DC voltage from leg 1 to leg 3 of all of the output transistors (the ones you changed). Post a list of the voltages and circuit board designation (FETxyz) for any that read more than 1v.

Do NOT let the probes short to other pins or to the heatsink when measuring the voltage.

Remember... High voltage and lots of stored energy. Be careful.

Apr 17, 2008 | MTX Thunder 1501D Car Audio Amplifier

2 Answers

Hi i have a mtx 1501 d


If it does it with no RCAs plugged in, the speakers or wiring need to be checked.

If the speakers and wiring are OK, the amp may have shorted output transistors.

Apr 10, 2008 | MTX Thunder 1501D Car Audio Amplifier

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