Hello everyone
Recently I've received a TEAC car amplifier for repair and at first glance just the outpu
t stage of one the channels was damaged.
Upon changing damaged power transistors with new ones from the same batch and applying power the amplifier was again shorted and went into protection mode.
Then I investigated further and found the presence of voltages near the rail voltage at the base of the power transistors and as soon as you apply input the final stage driver transistors BD139/140 will die and short out causing the amplifier going into protection mode.
I checked every single components in and out of the circuit and compare their value with other channels and couldn't find any noticeable difference between them.
And of course I check the input decoupling capacitor and it's not shorted.
I also tried changing all the transistors in the preamp section and still no luck.
Can anyone help me and explain what could cause such a fault?
Thanks in advance.
Recently I've received a TEAC car amplifier for repair and at first glance just the outpu
Upon changing damaged power transistors with new ones from the same batch and applying power the amplifier was again shorted and went into protection mode.
Then I investigated further and found the presence of voltages near the rail voltage at the base of the power transistors and as soon as you apply input the final stage driver transistors BD139/140 will die and short out causing the amplifier going into protection mode.
I checked every single components in and out of the circuit and compare their value with other channels and couldn't find any noticeable difference between them.
And of course I check the input decoupling capacitor and it's not shorted.
I also tried changing all the transistors in the preamp section and still no luck.
Can anyone help me and explain what could cause such a fault?
Thanks in advance.
Thank you for replying 🙏
On BD140 I can read -0.944V from GND to Base and -39.4 from GND to Collector and -0.378 TO emitter
And for the BD139 0.952, 39.4 and 0.365 respectively.
I tried using TIP41/42C instead of them and that resulted in two of the power transistors failing + the biasing D667 along side with them
But the TIP
s survived!
I didn't tried it again to make sure was that just two faulty power transistors or the problem was caused by the TIPs
Can I use these instead in your opinion?
But the TIP
s survived!
I didn't tried it again to make sure was that just two faulty power transistors or the problem was caused by the TIPs
Can I use these instead in your opinion?