JL Audio 300/2 Blown Left Channel

[SQ ABSOLUTE]

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.

[Perry Babin]

Is there any DC voltage on the speaker terminals of the blown channel (measured directly across the speaker terminals)?

[SQ ABSOLUTE]

-9.28 V DC.

[SQ ABSOLUTE]

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.

[Perry Babin]

Check the 10 ohm resistor near the second pin from the left.

[ashlar]

It reads 10 Ohm's.

[Perry Babin]

The 47k ohm resistors (large, marked 473) are known for bad solder connections. Check the connections. They typically need to have new solder added, be desoldered and re-soldered to remove the oxidized layer of solder.

[ashlar]

One reads 46.79k Ohm's

Other reads 46.85k Ohm's.

How do I go about desoldering/re-soldering a surface mount resistor? Do I need a special tool to do this?

[Perry Babin]

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.

[SQ ABSOLUTE]

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.