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Old 7th March 2005, 08:03 PM   #1
ADRIANd is offline ADRIANd  Mexico
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Unhappy mtx blown please help

I have an mtx blue thunder pro1502 i want to fix, but all the output transistors has burned and i do not know the part numbers, and the dc-dc transistors (4) are not there, so i dont know the part numbers either, i dont have the value of two resistors conected directly to the output transistors one to the right channel and one to the left,
could any one help me with my problem, the posision of the transistors npn and pnp in the board an the part numbres ?, thanks so much!
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Old 11th March 2005, 08:37 PM   #2
ADRIANd is offline ADRIANd  Mexico
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Unhappy PLEASE

PLEASE SOMEBODY WHO HAS AN MTX 1502 PRO WORKING THAT CAN SEE THE INTERIOR OF THEIR AMP AND TELL ME THE PART NUMBERS OF THE COMPONENTS AND RESISTORS, ANY HELP WILL BE APRECIATED
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Old 19th March 2005, 09:57 AM   #3
sdoom is offline sdoom  Germany
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Hi

I have a MTX RTA-2110.

In here there are 6 YTF541 . Those are not available in Germany . The replacements should be IRF541.

Usually you can use an IRF540 or an IRFZ48N for replacement on a big number of car-amplifiers.

The output transistors on my RTA2110 are 2SD1047 and compl. 2SB817 (specs: 100W , 12A , 160V)

You should be able to replace those with TIP35C / TIP 36C power transistors (in Europe you find those as BD249C and BD250C)
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Old 11th August 2005, 06:50 PM   #4
ADRIANd is offline ADRIANd  Mexico
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Thanks so much, but i'm not shure if your amp is compatible , anyway im going to try with that parts, could you tell me the value of the Resistances conected to the outpus transistors there is two bigger than the others and is one for the right channel and one for the left channel

thanks again Best regards
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Old 11th August 2005, 07:21 PM   #5
sdoom is offline sdoom  Germany
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hi


usually you dont do wrong with the TIP35 and TIP 36 power transistors. Those can be found in better Korean amplifiers and in old Hifonics power amps (series 8) They are actually pretty common as they can handle around 150W (or 25A) before they go up in smoke .

To find out where to place the NPN and PNP transistors simply follow the curcuit lines that run from the each transistors collector (center leg) to the SMPS s big capacitors (usually 2200F/35V or 1000F/50V)

You can check there, what is positive and what is negative supply voltage. PNP transistors are connected to the - voltage supply and NPN transistors are connected to + voltage supply.

Now for the adaptive resistors that go from each power transistor to the speaker output terminal is a bit trickey. If you use too small resistors the idle current could get too high and the protection curcuit (that measures the voltage dropped at the resistors) couls interact too late in cause of a fault/overload . If the resistors are to big, idle current could be too low and also the protection curcuitry could act too early ---> that means less output power.

Not sure about those. Usually with more output transistors per channel the resistors are a bit bigger, around 0,22 Ohms . I would go with that for a try. I assume you will find a potentiometer for each channel to adjust idle current. If there is no pot. than the amplifier uses an automatic idle current control curcuit. If so you will not have to worry about the output transistors at all as the control curcuit will adjust idle current automatically.


Well, but MTX has a big homepage , I would give it a try and write an email to an MTX-tech and simply ask for the part numbers and specs about the idle current.
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Old 11th August 2005, 09:16 PM   #6
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Most of the MTX class AB amplifiers that have FET outputs use IRF540s for outputs. If yours has 541s, the IRF540 is good replacement and is more readily available.

For the power supply, IRFZ48s should be OK. I think that they may have used IRF3205s or HUF75339Ps in the power supply originally.

As for the resistors, the other channel should have the same values. Since most amplifier channels are clones (or mirror images) of the opposite channel, use the other channel as a guide.
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Old 12th August 2005, 08:09 PM   #7
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The power upply transistors are almost always going to be some sort of FET, and they usually can be replaced with some other high current switching fets. IIRF-Z44's seem to be a good choice. But I don't know for sure, as I don't have an MTX amp lying around.

The output deviceswill either be MOSFETS or a pair of complimentary transistors. The emiter (or source) resistors will be the same, so you only need to find the value of one in the amp. They're usually .22 or .1 ohms. IF the amplifier uses bipolar transistors, the - supply rail will be using PNPs and the positive rail will be using NPNs. all of the NPN and PNP transistos in the amp will be the same number. Also, the transistors are complimentary, and the datasheet for one (example a NPN one) will say what it's complement is (which will be the PNP one the amp uses). So here you also only need to be able to get the number off one transistor in the whole amp to find out what all of them are. Some amps use MOSFET output stages, and MTX makes some noise about using n-channel FETs for both sides of the circuit. But I think they still have bipolar output amps.

You can usually tell bipolar or MOSFET output from the amplifier. if the transistor holes in the amp are makred BCE or SDG, you can tell Also, bipolar amps need a decent amount of current pushed into their bases to work, MOSFETs need no current (other than that to charge their gate capacitance). Look for the driver stage, if this is using some beefy transistors (I.E. some devices that look bigger than the usual small signal transistors), then it's probabally bipolar. You can also look at the rsistors in series with the gate or base of the output transistors. If this is only a few ohms, or under or not much more than ~10 ohms, it's most likely bipolar. If it's larger, like 50-100 ohms or something, it's most likely MOSFETs.

Remember, my suggestions are pretty generic, I don't have an MTX amp!
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Old 17th August 2005, 05:46 PM   #8
ADRIANd is offline ADRIANd  Mexico
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thanks everyone , i have not idea if this model uses bipolar or mosfets, and i dont have the value of the resistances so i can not know.
i wrote MTX but they did not respond my mails.

i not shure, but im going to try with that components,

ill keep you informed

Regards!
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Old 18th August 2005, 04:55 PM   #9
ADRIANd is offline ADRIANd  Mexico
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Thanks Dr photom an Perri babin, i saw the interior of the amp and i saw fets printed for the outputs, im going to use the IRF540




the resistors im talkin about are conected in parallel with the positive an negative of each channel one for right and one for left, i thik the resistors should be a high value in ohms, because if there were low, so much power will be wasted thru it,
could you recomend me some value?

excuse my bad english

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Old 18th August 2005, 05:11 PM   #10
sdoom is offline sdoom  Germany
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Please check if each resistor are also conncted in series to a capacitor, usually something around 100nF

If so, those are output filters. Usually something around 4,7 - 10 Ohms/2W are used for that.

as you can follow the curcuit board lines, two speaker terminals for each speaker should be connected together somewehre. Now this is GND potential.

I attached a small picture, this should be it if you follow the curcuit lines.


Click the image to open in full size.
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