JL Audio 300/2 Blown Left Channel

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I blew a left amp channel. It sounded like my left front door speaker had blown out. There was a loud pop - then no sound on the left side. The right side plays normally and the amp comes on with no issues other than no sound on the left side.

I opened up the amp and visually inspected it for signs of burned parts or smell but nothing was discovered.

How do I proceed?

Thanks.
 
Upon a closer look I noticed that there is a "Right" and "Left" daughter board. On the Right Channel daughter board, pictured on the left, there is ONLY one lighted-type surface mount device and it is lit GREEN as in the picture.

However, on the right side of the picture which is the Left Channel, there are THREE lighted-type surface mount device and they are all lit GREEN in the picture.
 

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You don't need 'special' tools but you'll need desoldering braid (liquid or paste flux if the braid isn't good quality - radio shack paste flux is messy but works well enough), solder and a soldering iron.

Do one end of the resistor at a time and you won't have to worry about getting it positioned properly on the solder pads.

There's no guarantee that this will solve the problem but it's a common enough problem that you need to do this before you do any more troubleshooting.
 
Okay, I will do the above, however.

While waiting for a response, I did some resistance checks. There is a 621 resistor that reads 16.47M Ohm. Using a lighted magnified, I discovered that that value is slightly defaced, probably caused by smoke. Nothing on the board is burnt. I couldn't see this with my naked eye.

A comparison of the right channel of resistor 621 reads .619k Ohm - being in tolerance.

What other component would have failed, causing the resistor to burn open? A shorted diode, maybe?

I figured it would have been a resistor problem as I 'scoped the amp last night via the TP1 and TP2 and noticed TP1 had a nice waveform with adequate amplitude and TP2 had a minutely small waveform, slightly above dc.
 
You are correct about the value. The 621 mentioned above is what was stamped on the body. As you know, 621 = 620 Ohm's.

I will check Mouser or Digikey for a replacement part and, while I am at that, purchase some of the other items you suggest getting on your Amplifier Repair website.

Thanks for all your help so far, until I get the above part ordered.
 
UPDATE

Replaced the 620 Ohm resistor and unseated the two big resistors and the left channel was restored. However, the left channel did not last for very long.

I again, replaced the 620 Ohm resistor as it had again increased in value. Unsoldered and resoldered those big resistors and now have the amplifier running on my test bench. Every now and then I would take voltage readings from each channel.

The left channel reads 27.75 VAC, unloaded.

Right channel reads 27.74 VAC, unloaded.

Bench source Rockford Fosgate RFX 8140. At max it clips the inputs of the amplifier at the minimum input sensitivity on the "High" setting which is 8 Volts.
 
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