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Old 2nd July 2008, 04:55 AM   #1
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Default Help to repair JL audio 300/2

I have been trying to repair this amplifier since 3 months.

It has been a headache!!

All the internal parts apear be fine.

The problem is:

It ignites of intermittent way.

turn´s on 15 seconds and turn´s of 5 seconds, turn´s on 15 seconds and turn´s of 5 seconds, etc.

Please help me before I take and...

This is the pic:

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Old 2nd July 2008, 10:08 AM   #2
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During the time that it's on, does it produce clean audio in both channels?

Is there excessive DC offset on either channel?

Does either channel have any oscillation on the output?

Does the cycle of on/off change when you change the position of any of the switches/potentiometers?
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Old 3rd July 2008, 03:43 AM   #3
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Quote:
Originally posted by Perry Babin
During the time that it's on, does it produce clean audio in both channels?

Is there excessive DC offset on either channel?

Does either channel have any oscillation on the output?

Does the cycle of on/off change when you change the position of any of the switches/potentiometers?

The amp produce clean audio in two channels and bridget, before shot down.

whitout signal:

without remote, the amp present 0.62 v DC in the outputs.

Whith remote, 0.006 V DC in the otputs


No changes, when I move switches and potentiometers.
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Old 3rd July 2008, 06:40 AM   #4
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Default more pics

I found other measurements rare in the power source:

Click the image to open in full size.
Click the image to open in full size.

They are without remote, only positive and negative applied
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Old 3rd July 2008, 06:52 AM   #5
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Without remote, those voltages are normal. If you apply remote, the voltage on pin 1 of the FETs will go to ~3-5v. The voltage on the rectifiers will probably go to approximately ±35v.

How many amps of current does the amplifier draw at idle (remote voltage applied, no audio).

Does it shut down with no speakers connected?

Are any of the indicators LEDs lighting except for the power LED?

Does the power LED go off when the amp shuts down?

What are you using to power the amp?
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Old 5th July 2008, 01:55 AM   #6
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Quote:
Originally posted by Perry Babin
Without remote, those voltages are normal. If you apply remote, the voltage on pin 1 of the FETs will go to ~3-5v. The voltage on the rectifiers will probably go to approximately ±35v.

How many amps of current does the amplifier draw at idle (remote voltage applied, no audio).

Does it shut down with no speakers connected?

Are any of the indicators LEDs lighting except for the power LED?

Does the power LED go off when the amp shuts down?

What are you using to power the amp?
The voltage on the diodes go 44 and -44 !!!!!!

4 amp current when apply remote.

Shut down only with speaker connected and at high vol.

Only the green led is turn on, and is always present.

I’m using one 12.5 v regulated power source (ASTRON) 1 - 25 A.

Today happen something different.

[img=http://img61.imageshack.us/img61/6824/dsc00944dw4.jpg]
[img=http://img61.imageshack.us/img61/6824/dsc00944dw4.b484ea5d27.jpg]

two resistors was burn, R300 and R301

¿this gives a track to find where is the problem?
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Old 5th July 2008, 02:35 AM   #7
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The voltage on the diodes go 44 and -44 !!!!!!

**** That's good. The board says the rail voltage should be 53v but its producing rail voltage so the power supply is probably OK.


4 amp current when apply remote.

**** That seem a bit high but could be due to the bias current being set too high.


Shut down only with speaker connected and at high vol.

**** This could be due to the 25 amp Astron power supply being insufficient to power the amp at high output power. When you get the amp working again, try running one channel at a time to see if the amp shuts off. If it plays at high power with 'either' channel and only shuts down when both channels are running at high power, the amp may be working properly and is simply shutting down due to low voltage.


Today happen something different.

**** If I'm not mistaken, those are (were) 10 ohm resistors. They are used extensively to provide protection for the regulated ±15v power supply. The caps provide additional filtering near the op-amps. I don't know why they would have failed. It's not likely to be part of the original problem. Is it possible that you didn't have the preamp boards plugged in correctly to the main board? You have to be careful connecting them. You need to replace them to see if they burn again. If they do, you may have a defective op-amp in that area.
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Old 5th July 2008, 03:42 AM   #8
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Quote:
Originally posted by Perry Babin
The voltage on the diodes go 44 and -44 !!!!!!

**** That's good. The board says the rail voltage should be 53v but its producing rail voltage so the power supply is probably OK.


4 amp current when apply remote.

**** That seem a bit high but could be due to the bias current being set too high.


Shut down only with speaker connected and at high vol.

**** This could be due to the 25 amp Astron power supply being insufficient to power the amp at high output power. When you get the amp working again, try running one channel at a time to see if the amp shuts off. If it plays at high power with 'either' channel and only shuts down when both channels are running at high power, the amp may be working properly and is simply shutting down due to low voltage.


Today happen something different.

**** If I'm not mistaken, those are (were) 10 ohm resistors. They are used extensively to provide protection for the regulated ±15v power supply. The caps provide additional filtering near the op-amps. I don't know why they would have failed. It's not likely to be part of the original problem. Is it possible that you didn't have the preamp boards plugged in correctly to the main board? You have to be careful connecting them. You need to replace them to see if they burn again. If they do, you may have a defective op-amp in that area.

The power supply is rigt for run the amp.

They shut down when is current only 6 A.

I change the resistors and the power suply is fine, + - 53V.

The voltage in the traks marked + /- 15 are +/ - 17V.

I have scope, if you see some more.
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Old 5th July 2008, 03:49 AM   #9
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Does the amp shut down if you run one channel at a time? There may be a problem with only one channel so this is something you need to check.

Did the resistors burn again after you replaced them?

±17 is OK.
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Old 5th July 2008, 04:03 AM   #10
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Quote:
Originally posted by Perry Babin
Does the amp shut down if you run one channel at a time? There may be a problem with only one channel so this is something you need to check.

Did the resistors burn again after you replaced them?

±17 is OK.
Now the amp shut down whit out speakers, or signal.

The resistors are fine after change; I find one broken cap too. I need to change. (I will change the two).
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