MTX Thunder2301

[rodner]

Hi guys. Working on a Thunder 2301. It has a SMD transistor marked 1GM that puffs smoke every time I apply the remote. ??? What is a 1GM and have you seen this before?

Thanks,

Roger

 

[Perry Babin]

The SMD Code Book

MMBTA06

If no one can answer your question, post a photo of the entire board and another of the area with the burns.

 

[rodner]

Will do. Thanks Perry!

 

[rodner]

Here are a few pics of the board. C131 was removed to take the pictures. Q201 is where I am seeing the puff of smoke.

 

[Perry Babin]

I have an amp here with the same transistor blown. It may take a day or two to study the circuit. If someone has a diagram for it, please post it.

 

[rodner]

I would appreciate any help, Perry!

 

[Perry Babin]

For your amp, what's the resistance between the main ground terminal and pin 4 of the LM311?

 

[rodner]

It's grounded. 0.3 ohms

 

[Perry Babin]

The following is from a 5601. It should be similar to your amp. I can't see how that transistor could burn, even though the one in this amp has also failed. I don't see any other failed components. You can right-click to zoom in on the photos.
http://www.bcae1.com/temp/mtx5601overcurrentprotection01.swf

 

[rodner]

I agree. There seems to be no reason for it to cook. I had a thought, though. This one came in with the 2 voltage regulators on the heatsink fried. One was a 317T. The other was melted to the point that I couldn't read it. Do you think it could have been different and using a 317 is causing the problem? I ordered a new transistor that will be here today. I will replace it tonight and see what happens.

 

[Perry Babin]

The 317 positive regulator is generally used with an LM337 negative regulator.

 

[rodner]

I hadn't thought of that. DOH! But I can't see where that would burn the transistor. Does the board you have use a 317 and a 337?

 

[Perry Babin]

No. It uses the more complex regulators using FETs, due to higher rail voltage.

 

[rodner]

Okay. I'm going to put a 337 in place of the one that cooked and replace the transistor that burned. Let you know how it turns out. Thanks a bunch!

 

[Perry Babin]

I don't have anything on the 2301. Before ordering the part, look up the datasheet and confirm that the input, output and adjust correspond to those on the 337.

 

[rodner]

Well it turns out that it was suppose to be an LM337T. I replaced it and the transistor that cooked. Powered it up and another SMD transistor fried. I believe the owner is going to call it a wash on this one. But, just to try, I've emailed MTX to inquire about a schematic. Not much hope for that happening, though.

 

[Perry Babin]

Which other transistor failed?

If you're successful in getting a diagram from MTX, you'll be the first. When working on car amps, you have to expect not to be able to get diagrams except from Rockford and the Japanese manufacturers.

 

[rodner]

The transistor that failed is on the opposite side of the board. I will shoot a picture of it, this evening.

I wasn't expecting a response from MTX. But I figured it wouldn't hurt to send an email. I really never expect to find much in in the line of documentation on anything 12 volt. It's sad that a company can build a product but not provide support information for it. But that's another thread, I guess.

 

[rodner]

Q419 is the one that smoked. Its marked 1D, as best as I can read it.

 

[Perry Babin]

Do you have a current limiter or a large current limiting resistor for the 12v supply?