I got a request from a friend of mine to have a look to his amplifier. When switching on "OVERLOAD" was displaying, however from time to time, message disappears and protection was removed.
I took some time in visual inspection (no bold caps, no solder joins, no burnt components neither hot burnt areas). I took some time to measure transistors and diodes. Everything seemed ok.
I realized that when OVERLOAD was on, pin 13 on IC601 (RSN307M44A-P) measured 5V. From time to time, when Amplifier was not protected pin 13 measured the right -1.5V
(Pin 13 goes through a 1K resistor to PIN 4 CP902 that goes to micro controller).
As long as everything else was measuring OK (no dc offset, no voltage on speakers), I decided to remove that 1K resistor (R663). At this point of time, amplifier was fully operational.
Without resistor, pin 13 on IC601 was measuring -12V. On the other side of the disconnected resistor I was measuring 5V coming from CP902 (micro controller). These two voltages were stable and didn't change during time!!
Why when connecting the resistor, voltage fluctuates from time to time between -1.2 and 5V triggering the protection? and without resistor voltages don't change and amplifier works "fine"?
Any understandable explanation? might be IC601 slightly faulty?
Regards,
Francesc.
I took some time in visual inspection (no bold caps, no solder joins, no burnt components neither hot burnt areas). I took some time to measure transistors and diodes. Everything seemed ok.
I realized that when OVERLOAD was on, pin 13 on IC601 (RSN307M44A-P) measured 5V. From time to time, when Amplifier was not protected pin 13 measured the right -1.5V
(Pin 13 goes through a 1K resistor to PIN 4 CP902 that goes to micro controller).
As long as everything else was measuring OK (no dc offset, no voltage on speakers), I decided to remove that 1K resistor (R663). At this point of time, amplifier was fully operational.
Without resistor, pin 13 on IC601 was measuring -12V. On the other side of the disconnected resistor I was measuring 5V coming from CP902 (micro controller). These two voltages were stable and didn't change during time!!
Why when connecting the resistor, voltage fluctuates from time to time between -1.2 and 5V triggering the protection? and without resistor voltages don't change and amplifier works "fine"?
Any understandable explanation? might be IC601 slightly faulty?
Regards,
Francesc.
