I have a Crown XLS 402D, that is about 4 years old. It would attempt to power up, then shut down due to the thermistor heating up from excessive current draw. So I put a 40W light bulb in series with the AC input, and started checking things at a safe current level.
I discovered that there is an oscillation in channel 1. I can make the amp run normally by doubling C107, removing C106, or even putting my DMM on the base of Q10, Q110, Q111, or Q102. I haven't found any bad components, and it's really got me stumped at this point.
Using my scope on x10 probe range, I can see the oscillation. The pulses are about 5uS wide and spaced around 10uS apart.
I discovered that there is an oscillation in channel 1. I can make the amp run normally by doubling C107, removing C106, or even putting my DMM on the base of Q10, Q110, Q111, or Q102. I haven't found any bad components, and it's really got me stumped at this point.
Using my scope on x10 probe range, I can see the oscillation. The pulses are about 5uS wide and spaced around 10uS apart.
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What is the voltage between Q118 and Q123 emitter to emitter? Should be <15mV DC
This amp will oscillate on low supply voltage. Don't let that fool you.
Place the input on a Variac and bring the mains up slowly whilst monitoring that voltage. That will tell you the nature of your fault.
I thought Crown had a 5year warranty.
This amp will oscillate on low supply voltage. Don't let that fool you.
Place the input on a Variac and bring the mains up slowly whilst monitoring that voltage. That will tell you the nature of your fault.
I thought Crown had a 5year warranty.
It went over 1 volt before the thermistor brought the power supply down.
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