Hello.
I received two ALTO TS115A active speakers for repair.
The amplifiers work in class D, they are two-way.
Power supplies - switched mode.
Below are the diagrams.
Both columns were loaned to the customer and returned damaged.
The same fault in both! (+ additionally in one a burnt woofer).
Unfortunately, the products are made in china and the construction is much poorer than provided for in the catalog notes of individual elements.
After turning on the power (with no signal source connected, gain-minimum) there is a slight "noise" in the speakers. When a signal is applied as the volume is turned up (the gain knob), the loudspeakers begin to play, but the sound is very distorted, as if the noise typical of digital circuits is superimposed. With a low volume of voice (increasing the gain), the overload protection is activated and the loudspeaker goes silent.
I've probably checked everything by now, and I'm spreading my hands out slowly.
In the power supply section, all branches "hold" the voltage values according to the diagram (measurement with a multimeter). These voltages do not change when the protection is triggered.
IGBT transistors, diodes and electrolytes on the w / n side of the power supply are measured - ok, the converter "does". On the low voltage side, electrolytes, diodes and stabilizers are fine, nothing gets hot. The tweeter power amplifier (TDA7254) seems to be working. The tip of the woofer (driver + mosfet transistors q104, q107) is working.
To be sure, I changed the driver and transistors of the LO terminal, TDA7254 of the HI terminals, transistors in the power supply converter, LM393 operational amplifiers in the security section. Unfortunately, no changes.
The only point I found was ripple on the power supply.
In the +/- 60V power section (powering the woofer power amplifier, I marked the diagram as + vcc and -vcc in red) there are ripples with an amplitude of about 0.35-0.45V at a frequency of about 285khz (respectively 3rd and 4th oscillogram ). I am writing "about" because I measured it with an old Soviet oscilloscope.
During this time, without powering the audio signal and without load, the HI and LO terminals, respectively, show the waveforms as in the photos below (HI - 0.35v / 285khz 2nd waveform, LO - 1.5V sine / 285khz 1st waveform) .
Could the problem be with the power supply?
I am counting on suggestions
I received two ALTO TS115A active speakers for repair.
The amplifiers work in class D, they are two-way.
Power supplies - switched mode.
Below are the diagrams.
Both columns were loaned to the customer and returned damaged.
The same fault in both! (+ additionally in one a burnt woofer).
Unfortunately, the products are made in china and the construction is much poorer than provided for in the catalog notes of individual elements.
After turning on the power (with no signal source connected, gain-minimum) there is a slight "noise" in the speakers. When a signal is applied as the volume is turned up (the gain knob), the loudspeakers begin to play, but the sound is very distorted, as if the noise typical of digital circuits is superimposed. With a low volume of voice (increasing the gain), the overload protection is activated and the loudspeaker goes silent.
I've probably checked everything by now, and I'm spreading my hands out slowly.
In the power supply section, all branches "hold" the voltage values according to the diagram (measurement with a multimeter). These voltages do not change when the protection is triggered.
IGBT transistors, diodes and electrolytes on the w / n side of the power supply are measured - ok, the converter "does". On the low voltage side, electrolytes, diodes and stabilizers are fine, nothing gets hot. The tweeter power amplifier (TDA7254) seems to be working. The tip of the woofer (driver + mosfet transistors q104, q107) is working.
To be sure, I changed the driver and transistors of the LO terminal, TDA7254 of the HI terminals, transistors in the power supply converter, LM393 operational amplifiers in the security section. Unfortunately, no changes.
The only point I found was ripple on the power supply.
In the +/- 60V power section (powering the woofer power amplifier, I marked the diagram as + vcc and -vcc in red) there are ripples with an amplitude of about 0.35-0.45V at a frequency of about 285khz (respectively 3rd and 4th oscillogram ). I am writing "about" because I measured it with an old Soviet oscilloscope.
During this time, without powering the audio signal and without load, the HI and LO terminals, respectively, show the waveforms as in the photos below (HI - 0.35v / 285khz 2nd waveform, LO - 1.5V sine / 285khz 1st waveform) .
Could the problem be with the power supply?
I am counting on suggestions
