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JL300/2 power supply problem? - pls help
JL300/2 power supply problem? - pls help
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Old 15th January 2019, 07:58 AM   #1
nonprof is offline nonprof
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Default JL300/2 power supply problem? - pls help

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!

Last edited by nonprof; 15th January 2019 at 08:02 AM.
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Old 15th January 2019, 12:46 PM   #2
Perry Babin is offline Perry Babin  United States
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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?
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Old 15th January 2019, 08:29 PM   #3
Cartel is offline Cartel
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JL300/2 power supply problem? - pls help
possible related?

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Old 16th January 2019, 01:14 AM   #4
nonprof is offline nonprof
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Quote:
Originally Posted by Perry Babin View Post
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!

Last edited by nonprof; 16th January 2019 at 01:19 AM.
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Old 16th January 2019, 01:19 AM   #5
Perry Babin is offline Perry Babin  United States
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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?
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Old 16th January 2019, 02:32 AM   #6
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Quote:
Originally Posted by Perry Babin View Post
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?
Thank you. I'll do.
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Old 17th January 2019, 01:47 AM   #7
nonprof is offline nonprof
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Quote:
Originally Posted by Perry Babin View Post
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!
Attached Images
File Type: jpg IMG_8262[1].jpg (143.1 KB, 36 views)
File Type: jpg IMG_8261[1].jpg (130.3 KB, 37 views)
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Old 17th January 2019, 10:16 AM   #8
Perry Babin is offline Perry Babin  United States
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Are there any broken legs on the rectifiers?
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Old 22nd January 2019, 05:18 AM   #9
nonprof is offline nonprof
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Quote:
Originally Posted by Perry Babin View Post
Are there any broken legs on the rectifiers?
Hello Perry, there are no broken legs at rectifier.

I notice that rail voltages are regulated at +-12Volts only. Do you have an idea how to raise the rail voltages?

Thanks
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Old 22nd January 2019, 09:02 AM   #10
Perry Babin is offline Perry Babin  United States
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Pin 1 is the feedback for the voltage regulation. It goes back to U701 on the PS driver board. Post the DC voltage on all terminals of U701.
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