Hello to all
I'm repairing a HARDSTONE amplifier in class D ...
The amplifier uses 3 driver cards.
The first (works correctly) generates the pwm, and the other 2, use AG & DK transistors on separate boards.
One of these, unfortunately, has failed some DK & AG.
DK & AG are 2SC4672 & 2SA1797, but they are untraceable by the various suppliers that I know (RS, TME, FARNELL etc).
What could I use instead of these?
Even in different package, for example, yesterday I installed BD139 & BD140, without mosfet output the square waveform is perfect (with a strong signal at 100hz at the input of the amplifier) but if I install the mosfet, the amplifier goes to protection.
I immediately thought that BD139 and BD140 did not do the job properly.
Mind you, I do not care about the transistor package, I can adapt without problems, I would like to know if there are valid substitutes of equal characteristics.
thank you so much
I'm repairing a HARDSTONE amplifier in class D ...
The amplifier uses 3 driver cards.
The first (works correctly) generates the pwm, and the other 2, use AG & DK transistors on separate boards.
One of these, unfortunately, has failed some DK & AG.
DK & AG are 2SC4672 & 2SA1797, but they are untraceable by the various suppliers that I know (RS, TME, FARNELL etc).
What could I use instead of these?
Even in different package, for example, yesterday I installed BD139 & BD140, without mosfet output the square waveform is perfect (with a strong signal at 100hz at the input of the amplifier) but if I install the mosfet, the amplifier goes to protection.
I immediately thought that BD139 and BD140 did not do the job properly.
Mind you, I do not care about the transistor package, I can adapt without problems, I would like to know if there are valid substitutes of equal characteristics.
thank you so much
Attachments
Without rail voltage i cannot make anything because all regulated voltages (+/-15v +6v) are generated via +/-RAIL..
So without rails, the amp dont turn on.
What do you mean by "vias"?
WITHOUT OUTPUT MOSFET, with an input signal at 100Hz, I see a perfect quadratic signal (which varies depending on the input signal) on the gates of all the mosfets.
After installing the mosfet, the amplifier goes into protection.
Can BD139 and BD140 replace 2SC4672 & 2SA1797 even if the package is different?
So without rails, the amp dont turn on.
What do you mean by "vias"?
WITHOUT OUTPUT MOSFET, with an input signal at 100Hz, I see a perfect quadratic signal (which varies depending on the input signal) on the gates of all the mosfets.
After installing the mosfet, the amplifier goes into protection.
Can BD139 and BD140 replace 2SC4672 & 2SA1797 even if the package is different?
Last edited:
oh, ok thanks for clarification!
I checked them and luckily there are no problems, because the tracks are under the board, only 2 are on the board but I have carefully welded them.
The board uses 2 amplification stages, each using 3 x irf640n and 4 x irf9640 (irf9640 are used in pairs).
I will post photos of the amplifier inside.
Attachments
Of the 3 original images you posted, is there a chip on the surface of the right-most 1 ohm resistor? Are the solder connection OK?
I'd like to know if the drive circuit can drive a load. IF you can easily remove the outputs (heating all 3 legs at once makes it easy), remov them and load one FET location leg 1-3 with a 1000pf cap and confirm that the drive signal remains at the same amplitude (about 10v), is being within 1v of the rail when turning off and is still square with the cap.
I haven't tried this, but you may simply be able to pull the center leg for all outputs to load the drive circuit. Should do the same as removing the rectifiers.
I'd like to know if the drive circuit can drive a load. IF you can easily remove the outputs (heating all 3 legs at once makes it easy), remov them and load one FET location leg 1-3 with a 1000pf cap and confirm that the drive signal remains at the same amplitude (about 10v), is being within 1v of the rail when turning off and is still square with the cap.
I haven't tried this, but you may simply be able to pull the center leg for all outputs to load the drive circuit. Should do the same as removing the rectifiers.
Good news, I solved the problem!
One of the 2 voltage regulators (7815) had a broken leg and I did not notice it.
In addition, the 7806 controller that in the picture I posted is missing (lower left), I replaced it with a 5.6v zener diode and its resistor to get 6v to power 74hc6040d starting from the positive controller 7815.
Now the amplifier works perfectly.
Thanks for your help, Perry.
One of the 2 voltage regulators (7815) had a broken leg and I did not notice it.
In addition, the 7806 controller that in the picture I posted is missing (lower left), I replaced it with a 5.6v zener diode and its resistor to get 6v to power 74hc6040d starting from the positive controller 7815.
Now the amplifier works perfectly.
Thanks for your help, Perry.
because before installing the mosfet, the leg of the 7815 regulator was not broken.
Later, when I installed the mosfets, overturning the board, the regulator hit the table in my laboratory violently, so it broke and I did not notice it.
I had done the replacement of 7806 with zener diode and resistor since the beginning of the repair.
hiuppyyyy!
Please, can you tell me why?
The circuit fed by the old 7806 absorbs very little current, for this reason, a zener diode is more than sufficient.
Just apply the electronics to understand that the zener diode can work well.
In fact, it does not heat up, it produces the right voltage that the circuit requires and finally, the amplifier works PERFECTLY!
The repairers are different from those who simply replace components because they are the ones that find solutions that are different from the original ones while maintaining the functionality of the electronic device altogether, and honestly it seems to me that I have done the second.
I see you know what you are doing, but...
the zener diode voltage changes with load and temperature and you will need a resistor that can dissipate your circuit load.
On the other hand the 7806 voltage regulator will be more tolerant and stable regarding input voltage/load/temperature.
Also it will have thermal protection, current limiting and less power dissipation.
Maybe there has been some thought behind to use a 7806. Nowadays they almost all cheap out where they can (and often where they can/should not, too).
If you have no time/parts you need to improvise, sure.
the zener diode voltage changes with load and temperature and you will need a resistor that can dissipate your circuit load.
On the other hand the 7806 voltage regulator will be more tolerant and stable regarding input voltage/load/temperature.
Also it will have thermal protection, current limiting and less power dissipation.
Maybe there has been some thought behind to use a 7806. Nowadays they almost all cheap out where they can (and often where they can/should not, too).
If you have no time/parts you need to improvise, sure.
Starting from positive regulated 15v, to obtain 6volt, a very low resistance is required to achieve this voltage with a zener diode.
In my case, I used a 100ohm 5watt resistor.
The heating of this resistor and of the zener diode is very close to zero, even after about 1 hour of continuous operation, demonstrating the fact that the resistor is calculated really well and that the circuit that needs to receive power, really absorbs very little current.
In my case, I used a 100ohm 5watt resistor.
The heating of this resistor and of the zener diode is very close to zero, even after about 1 hour of continuous operation, demonstrating the fact that the resistor is calculated really well and that the circuit that needs to receive power, really absorbs very little current.
my 2 cents...
Here in the US, if you're repairing equipment as a business, you will get a really bad reputation for doing shoddy work if you use something other than the exact replacement parts. If something you repair goes to another shop to be repaired again (same or different problem) and the tech sees something that's not OEM, they WILL tell the owner that the previous tech didn't use the correct parts. A few instances of this and word will get around quickly that your repairs are not reliable. The word gets around even more quickly in tight knit communities like car audio.
The exceptions are when there is a weakness in the design where using different parts make the amp more reliable.
That's here. Things are likely different in other parts of the world.
Here in the US, if you're repairing equipment as a business, you will get a really bad reputation for doing shoddy work if you use something other than the exact replacement parts. If something you repair goes to another shop to be repaired again (same or different problem) and the tech sees something that's not OEM, they WILL tell the owner that the previous tech didn't use the correct parts. A few instances of this and word will get around quickly that your repairs are not reliable. The word gets around even more quickly in tight knit communities like car audio.
The exceptions are when there is a weakness in the design where using different parts make the amp more reliable.
That's here. Things are likely different in other parts of the world.
I do not fix amplifiers for doing business, but for passion.
Of course, this passion can lead to economic gains, ridiculous, but they are still gains.
Precisely for these reasons (I do not do business and my profit is derisory) some times (IN CASES WHERE YOU CAN DO) I am forced to use equivalent parts or find alternative solutions to solve the problem, remaining unchanged the functions of the apparatus.
Obviously, in critical circuits, such as the output stage of class D amplifiers or SMPS power supplies where only original components are needed, I do not allow myself to change components with equivalences without using the brain.
In this case, before declaring the amplifier "perfectly repaired" I did some tests, stressing the amplifier, and I noticed that it behaves well ... clean audio, low source absorption, very low heating, like the original, and since the 7806 was dedicated only to 74hc4060d (which absorbs less than 20mA) I could say with certainty that the zener diode could be the ideal solution, in fact it was.
Obviously, when I do a repair like that, the amplifier owner agrees with me and most of all he wants to spend very little.
Then if someone else wants to argue or question certain jobs, most of the time it's just to prove superior and make people believe he can do better
Of course, this passion can lead to economic gains, ridiculous, but they are still gains.
Precisely for these reasons (I do not do business and my profit is derisory) some times (IN CASES WHERE YOU CAN DO) I am forced to use equivalent parts or find alternative solutions to solve the problem, remaining unchanged the functions of the apparatus.
Obviously, in critical circuits, such as the output stage of class D amplifiers or SMPS power supplies where only original components are needed, I do not allow myself to change components with equivalences without using the brain.
In this case, before declaring the amplifier "perfectly repaired" I did some tests, stressing the amplifier, and I noticed that it behaves well ... clean audio, low source absorption, very low heating, like the original, and since the 7806 was dedicated only to 74hc4060d (which absorbs less than 20mA) I could say with certainty that the zener diode could be the ideal solution, in fact it was.
Obviously, when I do a repair like that, the amplifier owner agrees with me and most of all he wants to spend very little.
Then if someone else wants to argue or question certain jobs, most of the time it's just to prove superior and make people believe he can do better
it is not disturbance ..
it's from the beginning of the thread that I said what it was.
Do not worry, whatever you say, I treasure and learn new things that I can then use to improve my technique.
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