In Class H circuits, faulty steering diodes or MOSFETs can prevent the amplifier from switching to the high-voltage rail, causing premature audio clipping. If you need help with a specific repair, tell me:
: Check for shorted collector-to-emitter junctions on the power BJTs. Always replace them in matched pairs. Failed Class H Commutators nx audio rx 4000 circuit diagram
: A specialized system protection circuit is a core feature, providing: Short Circuit & Overload Protection : Prevents damage during output faults. DC & Thermal Protection : Guards against DC offset at the speakers and overheating. Soft Start : Reduces inrush current during power-up. Signal Processing : Includes built-in 120Hz Hi-Pass and Low-Pass filters In Class H circuits, faulty steering diodes or
| Symptom | Likely Circuit Area | Components to Check | | :--- | :--- | :--- | | | Output Relay / Protection | Check the protection transistors and the relay coil voltage. Check for DC offset on the output pins. | | Distorted Sound | Bias Circuit / Output Stage | Check the Vbe multiplier (bias transistor) on the heatsink. Test output transistors for shorts or opens. | | Amplifier Blows Fuses | Power Supply / Shorted Outputs | Disconnect mains! Use a multimeter to check resistance across the power supply capacitors and output transistor legs (C-E junction). A dead short indicates blown output transistors. | | Hum/Buzz | Power Supply Grounding | Check filter capacitors for drying out (loss of capacitance). Check "Ground Lift" switch functionality and input cable shielding. | | Overheating | Bias / Fan Control | Is the fan spinning? If not, check fan voltage. If fan runs but amp is hot at idle, the Bias Current is set too high (adjust bias trimmer pot). | Failed Class H Commutators : A specialized system
If you have measured any across the main rails or output terminals.
Steps up the low-voltage input signal to a high-voltage swing.