mtx blown please help

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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 don´t know the part numbers either, i don´t 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!
 
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)
 
Thanks so much, but i'm not shure if your amp is compatible , anyway i´m 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
 
hi


usually you don´t 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 2200µF/35V or 1000µF/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.
 
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.
 
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!
 
thank´s 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 i´m going to try with that components,

i´ll keep you informed

Regards!
 
Thanks Dr photom an Perri babin, i saw the interior of the amp and i saw fets printed for the outputs, i´m going to use the IRF540


:) :) :)

the resistors i´m 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¡¡

:xeye:
 
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.


An externally hosted image should be here but it was not working when we last tested it.
 
I have an MTX 2300 here that has a 680 ohm 2 watt resistor across the output. It's not a zobel. There is no capactor in series with the resistor. If your amplifier is designed the same way, the value of yours may be somewhat different due to the difference in power output.

If the resistor IS in series with a capacitor, 10 ohms would be a common value.
 
Thanks Sdoom and Perry Babin, your comments was so helpfull,
and there are no capacitor in series with the resistor, is just conected to the output channel, i think i could try 680 ohms 2W the amp gives 150 rms per channel @2 ohms two channels it has two fuses of 30 Amperes each one.


:cool: :cool: :cool:
 
Perry i was looking the data sheets of the irfz48s and the irf3205s and there is a diference between the continuos drain current they can handle, the z48 handles 50 A and te 3205s can handle 110, if i put the z48 will not afect the performance of the amp? because originally use 3205 s.
 
If it originally had 3205s, then that's what you need to use.

If you don't know what was in it, the Z48s aregenerally a better choice because they're easier to drive. If it has the small driver transformer between the PWM IC and the FET gates, the 3205s will be fine. I use the 3205s in all of the MTX2300s that I repair. They hold up well and cause no problems.

A note on the continuous drain current of the 3205s... The datasheet states that the actual, usable drain current is limited to 75 amps (due to the limited current capacity of the package). The extra current capability really only becomes useful at higher temperatures where the FETs would be derated.
 
Perri, one question if my amp originally have irf48s, and i put irf 3205s, i mean if i put a fet that handles more current , but the voltage and Rds(on) are similar it will afect the performance of the amp?...??

or ..only afect the performance of the amp when you put a fet with a lower drain current??


:confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused: :confused:
 
hi ADRIANd ,

it´s not that simple with the SMPS (switching power supply) mosfets. For a 30A fuse a pair of IRFZ34 would still be ok, but you will not find any SMPS that will drive the mosfets all the way to the mosfet´s limit concerning the current capabilty of the fet .

the SMPS is a whole system and depending on the setup and the power it has to handle there are different kinds of mosfets used. Also, the manufacturer tries to save money and usually you will find similar parts in a whole variety of amplifers. (korean amplifiers use IRFZ44 most of the time)


The older MTX I have all use the YTF541 , regardless if it is a 4 or a 2 channel amplifier. Both SMPS look pretty much alike.


When you need to use other mosfets than those originally installed there are some things to be taken into account.It is not only the drain current or power handling of the fet. You first need to get the datasheets and compare the capacity values of the original fet and the fet you want to use as a replacement. Depending on those values you may have to (or not if the capacity values of the fets are quite similar) replace the Gate-resistors, too.

For example: An SMPS uses IRFZ34 mosfets and you want to replace those with IRFZ44 (because those can handle more drain current and more power) . Now depending on the setup of the SMPS ( frequency, dead time , etc) you can leave the original gate resistors as they are. But I would suggest to replace the resistors with a smaller value. Let´s say there are 100 Ohm resistors in the original curcuit with the IRFZ34, I would use 82 Ohms or 68 Ohms with the IRFZ44 . This is because of the capacity values of the mosfets. If this is not taken into account, the SMPS could fail when the amplifier causes a high current draw because the mosefets might not act fast enogh anymore. This often results in a total burn of the mosfets because the timing fails and both mosfet - banks are opened at the same time, causing a short through the transformer wire.

Here is a picture of what can happen.



So it is always easier to use the original mosfets in the SMPS if they are available.



Steph
96_1_b.JPG
 
ok comparing the data sheets of the mosfets irfz48 and irfz3205

are similar irfz48 Vdds=60 Rds=0.018ohms id= 50a

irf3205s Vdds= 55 volts Rds=0.008Ohms id=110 a

i going to check the other parameters and decide wich i going to install, if the amp has two fuses of 30 Amperes there is 60 Amp total i Think irfz48 is ok
 
You will see no difference in performance between the z48s and the 3205s. The 3205 may run cooler under heavy loads.

Does that amplifier use the driver transformer or does it drive the FETs directly?

If it doesn't have the driver transformer, use the Z48s. If it has the driver transformer, you can use either transistor.

If you've determined what transistor was originally used, that's what you need to use.
 
Yes between the PWM IC and the gates there is a small toroid transformer, one coil feeds two fet´s gates and the other coil feeds the other two, there is 4 for fets in total, i think i´m going to use 3205, i think that way the amp will respond better to the high current demand, and also will work a little cooler.
 
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