Hi!
I'm not sure if this is the best forum since my question might straddle a few subforums. If there is a better place for it please let me know.
I got a Definitive Technology Mythos ST that has blown transistors in its built-in subwoofer amp. I'm trying to find out if it would make sense to replace the transistors or just replace the whole transistor board. From what I've been able to gather, it's most likely a (version of) DS-300 module but he transistors have the markings removed. Even though it looks just like the board in Mythos STS I don't know if they're identical. The transistors in the STS still have their markings. I'm including pictures of both for reference.
Does anyone know if the transistors in the ST are the same as in any other DS-300 board and if it would make sense to replace them? Or if I should just swap the whole board and is it available anywhere? Did anyone make a repair like that?
FYI: I moved the transistor board from the good ST to the malfunctioning one and it worked. So it seems that the problem is with the transistor board.
I'm not sure if this is the best forum since my question might straddle a few subforums. If there is a better place for it please let me know.
I got a Definitive Technology Mythos ST that has blown transistors in its built-in subwoofer amp. I'm trying to find out if it would make sense to replace the transistors or just replace the whole transistor board. From what I've been able to gather, it's most likely a (version of) DS-300 module but he transistors have the markings removed. Even though it looks just like the board in Mythos STS I don't know if they're identical. The transistors in the STS still have their markings. I'm including pictures of both for reference.
Does anyone know if the transistors in the ST are the same as in any other DS-300 board and if it would make sense to replace them? Or if I should just swap the whole board and is it available anywhere? Did anyone make a repair like that?
FYI: I moved the transistor board from the good ST to the malfunctioning one and it worked. So it seems that the problem is with the transistor board.
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A first check would be to see if bass driver has blown blowing up amplifier.
Also, you need to find out what else has blown with outputs as just replacing outputs might not be enough or they might blow again.
I guess simplest way is replace amp but check speaker too for low impedance.
The voice coil can cook melting resin on copper wire which then causes a short or low impedance.
If speaker is 8 ohms then DC resistance will be about 6 ohms.
If speaker is 4 ohms then DC resistance will be about 3 ohms.
If they are much lower its likely voice coil is fried.
Also, you need to find out what else has blown with outputs as just replacing outputs might not be enough or they might blow again.
I guess simplest way is replace amp but check speaker too for low impedance.
The voice coil can cook melting resin on copper wire which then causes a short or low impedance.
If speaker is 8 ohms then DC resistance will be about 6 ohms.
If speaker is 4 ohms then DC resistance will be about 3 ohms.
If they are much lower its likely voice coil is fried.
The drivers tested fine. After some poking around I found some resistors were testing open. Since the replacement resistors and transistors were not expensive, I just decided to install them and see what happens. Lo and behold! It's working! I'm all set for now. Thanks!
Nice write up.
Which DS 300 module are u referring to?
I have a pair of sts, with one defective amp... Would be nice to get it in order again.
Tnx
Hello, thanks to dear Druuber, I now know the marking of transistors! The scheme or service manual on Mythos ST cannot be found anywhere. I am repairing the same amplifier, the output stages are short-circuited, the marking in the board has been erased from some elements, so I ask for help in determining the elements, please help!
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The same small amplifier board are used in audio vector C sub....
I've struggling with the same issue on my BP 7004....
I've struggling with the same issue on my BP 7004....
I also had a break for the subwoofer, there was a break in the variable resistor - the volume control at 5kOm (always check it!), because of it, crackling first appeared, leads and self-excitation of the output stage occurred, the field-effect transistors shorted out, the track from the diode bridge of the power supply circuit burned, but it looks like you still need to change the transistor control driver, this is how about the same chip that is in the photo 1,2
I'm still doing the switching circuit, while this chip resembles an operational amplifier on switching, maybe it's TL072
Hey All I also having problems with my Mythos Sts , where it would started popping and making crackling noises! Hard to find info on these things so far I have replaced the big Caps 6800UF 80 V , no change in the behaviour of the speaker , then decided to dig further and found this forum , does anyone know if my problem could be this transistors , I am rookie when it comes to electronics but good at soldering I have pulled the transistors off the board and attempted to test them just confused on test procedure also I am not getting any Resistance going from source to Gate which makes me think that transistors are fried I get reading from source to drain of around 0.539 , if anyone that has successfully component swapped the board and was successful could please help me with this issue thanks
Hello, the transistors are most likely intact, there is no point in changing the capacitors, but you need to check them, check the transistor control resistors on the output amplifier board, I had the same problem, the resistor burned out.
Hello you are right the transistors were intact as I tested them with a transistor tester , just not sure where the transistor control resistor is on the board as I mentioned I am rookie this is my first amp I am working on here is picture I have taken the transistors are removed but will be put back soon , your help is greatly appreciated thanks
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Hello, the resistor marked 103 has a nominal value of 10 kOhm, the circuit has high-resistance elements, check everything very carefully, all resistive ceramics are of disgusting quality, so look at all resistors.
I just ordered resistor pack off Amazon will start checking all but yea as soon as I remove that one the other resistor marked 103 showed proper value so I am guessing the 103 I removed was defective , also I don’t know why this board is so weird the holes for the transistors don’t go all the way through, the same pads for the transistors is damaged when I removed them can’t see where the middle or the right pads go go the left one goes to that 103 resistor I wish they sold replacement boards