MTX Thunder 4122

[jkrokenberger]

Hi there, I have an MTX Thunder 4122 that powers up and plays. It has a problem though, D93 has shorted and burned a trace to ground. D93 is in the input section of the amp. It is a simpler amp with only a hi/lo/full pass switch and gain control. Any help would be appreciated.

 

[Perry Babin]

Photo?

 

[jkrokenberger]

The diode, D93 has the anode tied to RCA ground and the cathode to power ground. The trace from cathode to power ground is burned, diode is measuring shorted. The amp plays fine as it is now, I can get photos in a little while. I am suspecting the amp had the main ground wire lose connection at one time, could that cause the problem?

 

[Perry Babin]

That's right. Remove and don't reinstall the diode. There should be a parallel 1k resistor and another identical diode with a reverse connection. Those should be checked. Without a photo, I'm assuming that this amp is like many of the older MTX amps.

 

[jkrokenberger]

There is a parallel 1k resistor but D93 is the only diode in that area. This amp is a surface mount version of the Pleitz design Thunder 250x. While not identical it is very similar.

So, remove the diode and repair the trace then?

 

[Perry Babin]

If the anode was connected to the RCA jacks, it's a later version where the one that could burn when the amp lost ground had already been omitted. What probably happened was 12v was allowed to contact the RCA shields. The trace will be need to be repaired. I'd replace the diode in the later design with only one diode.

 

[jkrokenberger]

Thank you sir. I will do that and see how it goes. I will report back.