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.