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Old 22nd September 2008, 08:58 PM   #21
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I don't have a 300/2 here but the 500/1 I have here has a very similar circuit and the FET (IRFZ44) runs cool. Measure the voltage across the 33 ohm resistor near the transformer. This amp has 3v DC across the 33 ohm resistor. Yours should have something similar. If it's significantly more, there may be a problem.

If you have a scope, measure the peak voltage of the gate drive signal on Q510. If I'm not mistaken, your amp uses the 3843 driver IC. If so, you should see a drive signal of ~10v peak.

The 4 amps of current draw could be from the biasing of the audio amplifiers. Before you try adjusting them, measure the DC voltage across the test points. Be careful not to allow the probes to contact the busbars.
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Old 22nd November 2008, 07:05 PM   #22
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Default Im back!!!

Quote:
Originally posted by Perry Babin
I don't have a 300/2 here but the 500/1 I have here has a very similar circuit and the FET (IRFZ44) runs cool. Measure the voltage across the 33 ohm resistor near the transformer. This amp has 3v DC across the 33 ohm resistor. Yours should have something similar. If it's significantly more, there may be a problem.
Yes, have a problem, one side has 11.13V and the another side 14.4V
Quote:
Originally posted by Perry Babin

If you have a scope, measure the peak voltage of the gate drive signal on Q510. If I'm not mistaken, your amp uses the 3843 driver IC. If so, you should see a drive signal of ~10v peak.
You are right, it use the 3843B

this is the wave form from the gate of Q510 set at 5us and 5v.
Click the image to open in full size.Click the image to open in full size.

This is from the Drain:
Click the image to open in full size.Click the image to open in full size.

And the source:
Click the image to open in full size.Click the image to open in full size.

Quote:
Originally posted by Perry Babin
The 4 amps of current draw could be from the biasing of the audio amplifiers. Before you try adjusting them, measure the DC voltage across the test points. Be careful not to allow the probes to contact the busbars.
The + - 53V its ok

+ - 15 is now + - 17V, but I think its by the actual failure.

another comment: the two IC 74VHC132 are very hot.
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Old 22nd November 2008, 07:29 PM   #23
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14.4-11.13 is close enough to 3v across the resistor.

What is the voltage on pin 14 of the 74vhc132?

The waveforms look OK.
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Old 22nd November 2008, 07:46 PM   #24
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Quote:
Originally posted by Perry Babin

What is the voltage on pin 14 of the 74vhc132?

Pin 14 is 8.33 V
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Old 22nd November 2008, 08:21 PM   #25
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It should be ~5v. You'll have to try to find the 5v regulator.
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Old 17th March 2009, 09:39 PM   #26
sheim is offline sheim  United States
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Default Board location for Jfets?

I would like to ask you some questions about this Amp.
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Old 18th March 2009, 03:00 AM   #27
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If you're looking for a response from someone specifically, you should ask for them by name.
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Old 18th March 2009, 04:17 PM   #28
sheim is offline sheim  United States
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Default IRF540N pcb board locations

There are two of these out of 8 and need to know where the two IRF540N go?
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Old 18th March 2009, 11:31 PM   #29
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If I'm not mistaken, all 8 of the output transistors (connected to the large white resistors) are IRF540s. The N suffix part is essentially the same as the IRF540.
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Old 19th March 2009, 03:58 AM   #30
sheim is offline sheim  United States
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Default JL Audio 300/2 fets

Perry,

Thank you for your reply. The reason I ask this question is because the IRF540 is rated for 100 Volt , 28 Amp , and 150 Watt.

The IRF 540N is rated at 100 Volt 27 Amp and 94 Watt.

I did not notice this till after I had removed all 8 of them. If this is not that much of a differance in there values I my have other problems.

Steve
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