JL300/2 power supply problem? - pls help

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Hi!

Somebody help me on JL amp 300x2? dont have problem if the volume level is minimum and low. But If you increase the volume/gain the rail voltages drops to +-12volts or lower and sound output become distorted. I notice if no load, the rail voltages just reaches to +-24V, I know these voltages are low and not normal.

Checking the signal at primary and secondary transformer, I can't see a perfect square wave coming in and out.

Happy New year! Thank you!
 
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The supply is heavily regulated so there will be no square wave. For some amps, you can reduce the input supply voltage to force a perfect square wave but the low-voltage shutdown in this amp may shut the amp down before you get to a perfect square wave.

Is the waveform on the primary collapsing when the rail voltage drops?
 
The supply is heavily regulated so there will be no square wave. For some amps, you can reduce the input supply voltage to force a perfect square wave but the low-voltage shutdown in this amp may shut the amp down before you get to a perfect square wave.

Is the waveform on the primary collapsing when the rail voltage drops?

Hi Perry, The primary and maybe the secondary waveforms too, making a nice square wave when the rail voltages drops or increasing the sound level. The sound becomes distorted too. Thanks!
 
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If the waveform is going square on the gates and the drains and the drains are swinging to 2x the supply voltage, I'd suspect that the problem is on the 12v supply line. Can you use a supply that will keep the input voltage well over 12v?

Hello Perry, I confirmed that my 12V supply not drops below 12v, I monitored it on the top(Drain) of power mosfets and at the terminal of the power supply.

I have a question

1.Why my rail voltages is measuring +29V and -22V (neg probe on -supply) only with load. And It drops when has a load and kickin. What is the normal rail voltages without load?

Other symptoms:
- There is no LEDs lit coming out...
- When there is a music the rail voltages drops to +-12V, respect to -supply.
- Turning off the amplifier through remote signal, you can still hear a very low music and gone.

Please see attached image taken from the output rectifier with load. looks nice...

Thank you!
 

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Leaky? Electrically?

Were they heating up?

If you have removed them, re-check the rail voltage. They could have been pulling down the reference used by the rail regulator circuit. I think pin 5 on U701 should be near 2.5v.

Yes, the logic gates/FF were about 30 ohms and 100 ohms on their power pins. The 3 pins nearby not sure it is regulator or transistor is heating so I removed the ICs and the heating went away.

Thank you Perry! I will replace the two ICs and let you know!
 
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