Don Oleg wrote:I had detected in some disks that the 0 ohm resistor of the 5V line had degraded to 10-20 ohms causing a drop in 5V feed.
In other cases i have noticed that when disk clicks the negative -5V flicks, but in this case can not arrive to a good conclusion.
That's very interesting. However, I think you will find that very few, if any, people actually measure anything. Instead they usually just swap boards and move the "ROM".
One observation I have in regard to the -5V supply is that it is usually generated by the motor controller IC and can be switched on and off via a command from the MCU. So if the MCU does not detect the preamp, or if it detects a fault in that area, then it can switch off the -5V supply. It may even do this during standby, but I've never checked this.
If you suspect a problem with the -5V supply, perhaps you could add additional capacitance in parallel with the output cap. I would use a high frequency ceramic cap.