Hello!
I'm not very experienced at diagnosing and repairing audio equipment.
This is a Chinese made DAP Audio CX-2100 very similar to CROWN Xli 800 definitely made in the same factory
The amp in the schematic is a class G and exhibits DC on output channel 2, varying from 100mV to 3V (Channel 1 has 6mV) and crackling when a speaker is connected both rails have steady +49V and -49V.
Most of the time AC current draw is steady at 200mA (and responds as expected to WR1 and WR2), but a couple of times I had a pulsing current draw (I could hear the transformer) and measured it pulsing all the way up to 800mA
I have removed the power transistors Q85 to Q87 and Q91 to Q93 and replaced with a single 2SC6200 (and complimentary PNP) for testing but no change
Also removed the "iDrive" mosfets Q70 and Q73 but no change
Once I measured "Middle 2" to ground as -2V and at the same time voltage across D81 was 49V and D84 was 43V something is causing this difference
Base to Emiter volage on the power transistors 30mV
Voltages at Q78 and Q79 are very close to the same transistors on channel 1 (Q77 and Q80)
Surprisingly (for me) the protection circuit is not on
And this is as far as I got!
I'm stumped since nothing is obviously burnt but something is definitely wrong
Can someone please help me on what to do next
Thanks
I'm not very experienced at diagnosing and repairing audio equipment.
This is a Chinese made DAP Audio CX-2100 very similar to CROWN Xli 800 definitely made in the same factory
The amp in the schematic is a class G and exhibits DC on output channel 2, varying from 100mV to 3V (Channel 1 has 6mV) and crackling when a speaker is connected both rails have steady +49V and -49V.
Most of the time AC current draw is steady at 200mA (and responds as expected to WR1 and WR2), but a couple of times I had a pulsing current draw (I could hear the transformer) and measured it pulsing all the way up to 800mA
I have removed the power transistors Q85 to Q87 and Q91 to Q93 and replaced with a single 2SC6200 (and complimentary PNP) for testing but no change
Also removed the "iDrive" mosfets Q70 and Q73 but no change
Once I measured "Middle 2" to ground as -2V and at the same time voltage across D81 was 49V and D84 was 43V something is causing this difference
Base to Emiter volage on the power transistors 30mV
Voltages at Q78 and Q79 are very close to the same transistors on channel 1 (Q77 and Q80)
Surprisingly (for me) the protection circuit is not on
And this is as far as I got!
I'm stumped since nothing is obviously burnt but something is definitely wrong
Can someone please help me on what to do next
Thanks