PWM output voltage is just only 0.14Vrms!

[nonprof]

Hello there!

Kindly let me know if it is normal for PWM of JLHD 750/1 to have output of 0.14Vrms using my DC meter. The problem of this amplifier is growling sound at the speaker and smd capacitors are bursting at output section. My rail voltage is 120VDC! is it higher? please help me to this amp, ive invested a lot of money here....
thank you and more power to DIYers!

[Perry Babin]

I have no information on this amp but here are some generic answers.

Your meter may not have the frequency response to read high frequencies accurately. It's generally only the most expensive meters that can read over ~500Hz accurately.

If the rail voltage is not too low, the drive signal is likely OK.

The JL 1000 has a rail voltage of 115v. 120v may be a bit high but maybe not. If the working voltage of the rail caps is greater than the rail voltage, 120v may not be a problem.

Is the voltage across the SMD caps greater than their working voltage?

What's the DC voltage on the positive and negative speaker terminals? Place the black meter probe on the amplifier's ground terminal.

Does it make noise with no RCAs plugged in?

[nonprof]

Originally Posted by Perry Babin

I have no information on this amp but here are some generic answers.

Your meter may not have the frequency response to read high frequencies accurately. It's generally only the most expensive meters that can read over ~500Hz accurately.

If the rail voltage is not too low, the drive signal is likely OK.

The JL 1000 has a rail voltage of 115v. 120v may be a bit high but maybe not. If the working voltage of the rail caps is greater than the rail voltage, 120v may not be a problem.

Is the voltage across the SMD caps greater than their working voltage?

What's the DC voltage on the positive and negative speaker terminals? Place the black meter probe on the amplifier's ground terminal.

Does it make noise with no RCAs plugged in?

I did measures PWM out from other JL 600/4, I got 1.5V something.
The filter caps has a 160VDC rating, it's higher from rail voltage.
If JL 1000 has a 115VDC rail voltages then the 750/1 schematics says correct with a rating of 105 rail voltage for 750wattsrms - so I must get this value.

From defective JL750 I notice the PWM Duty cycle is very small, thats why it gives only 0.15VRMS. This is not usual...

The voltages on ouput terminal goes low and high! If I touched with my fingers I feel electricity, and some ceramic caps popping and burst.
SMD caps rated as 200V connected on output speaker terminals.

EVen without signal processor the speaker growls and caps burst.

Thanks to your reply...

[Perry Babin]

IF the rail voltage is too high, you don't want more drive. That would make it even worse.

If you have the schematic diagram, email me a copy. It will make it much easier to help.
babin_perry@yahoo.com

[nonprof]

Originally Posted by Perry Babin

IF the rail voltage is too high, you don't want more drive. That would make it even worse.

If you have the schematic diagram, email me a copy. It will make it much easier to help.
babin_perry@yahoo.com

you got email Babin...thanks in advance!

[Perry Babin]

Did you measure the rail voltage on the rectifier or on the output transistors?

[nonprof]

Originally Posted by Perry Babin

Did you measure the rail voltage on the rectifier or on the output transistors?

rectifier is something 105VDC I guess...120VDC rail voltage at the output FET transistor, drain or source.

[Perry Babin]

The rectifier reads higher than the outputs in some amps that have inductors (like this one). Re-measure the voltage at both points. If it's easier to get to the two terminals of the filter inductor, you can measure the voltage there.