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Old 26th August 2013, 10:21 PM   #1
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Default JL500/1 No Power

Got one of these that is a tough dog. Everything is fine, except there are no LEDs, draws no current, its as if it has no remote signal. Matter of fact, thats exactly what it is.

I know the remote circuitry is on the pre-amp PCB. So i swapped another pre-amp PCB from a known good unit in, The amplifier powers up and works fine.

but the original pre-amp PCB does not. So i begin checking transistors around the LM324 circuit. (remote circuit) and am coming up empty. Even checked all the resistors, they are fine.

There is a 5-leg SOT23 transistor that has a Marking N09 B or it might be 60N. Not sure. Cant find any data on this part. Closest thing I found was an Analog Devices watchdog/reset management controller and i know this isnt right. the pinning isnt the same.

The working board has 1.8V between the 22K resistors next to that part. The non-working board has 7.3V there. with 0V on the other side whereas working board has 5V.
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Old 27th August 2013, 01:24 AM   #2
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Have you applied remote voltage to the amp and probed throughout the boards traces and components to see where you lose it?
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Old 27th August 2013, 02:49 AM   #3
kds9591 is offline kds9591  United States
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It might not be a component failure. JL amps often have problems with a lack of plating or corrosion in the via's(plated through holes) causing open traces.

Trying to just eyeball them is not enough as even under magnification they can look good but are not. Check the traces for continuity in the remote circuit and any that you are unsure of where they go (ex:trace goes under a component) check against the known good board you have for comparison.
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Old 27th August 2013, 12:00 PM   #4
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Look for any feed-throughs that have a green powdery substance in them. Do not clean the board. The images below show the substance before and after cleaning. The defective feed-throughs are easier to find before you clean the board.

You may need a high-power lighted magnifying glass to see the damage.
Attached Images
File Type: jpg IMG_8943b2x.jpg (169.5 KB, 49 views)
File Type: jpg IMG_8921bx.jpg (92.9 KB, 47 views)
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Old 27th August 2013, 01:59 PM   #5
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Well, I found a Rev3 preamp boad in my junk bin. (Rev10 is whats in here).

All it does is smoke Q401 on powerup. But it does powerup. lol. I replaced Q401 and D401 from the other board and it still wants to overheat Q401.

Odd...
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Old 27th August 2013, 02:17 PM   #6
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I looked over it, I dont see anything corroded as such, I checked them all, and they came out good. I did however find a hairline crack in the resistor R416 So I will swap that out and see what happens.
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Old 27th August 2013, 02:21 PM   #7
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When you state that it powers up, do you mean that it will produce clean audio?
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Old 27th August 2013, 02:57 PM   #8
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That fixed it. Wonder how a resistor developes a hairline crack like that. It shows no signs of heat stress....

This is on the original Rev10 board. I pulled the rev3 board that kept smoking the transistor and tossed it back in the junk parts bin.
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Old 29th August 2013, 03:30 AM   #9
kds9591 is offline kds9591  United States
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Quote:
Originally Posted by mbates14 View Post
That fixed it. Wonder how a resistor developes a hairline crack like that. It shows no signs of heat stress....

This is on the original Rev10 board. I pulled the rev3 board that kept smoking the transistor and tossed it back in the junk parts bin.
Thank you for posting your repair conclusion. So many of these car amp repair threads start out well but end up being cliffhangers with no conclusion.
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