HiFonics BXi1608D

[adelphia83]

I have a HiFonics BXi1608D that I purchased refurbished that's been working fine for about a year and a half.

Out of the blue, turned the stereo up and noticed no bass, turns out the protection light is on. Removed said amp from vehicle, placed it on a test bench, and protection light comes on immediately at startup. Draws normal current at idle, < 1 amp.

The amp is never really driven hard, so I think it's unlikely the failure is due to stressed components. A visual inspection inside the amp does not reveal any burnt or suspect parts.

Ideas and suggestions on where to start? I have a meter and basic tools, but no scope. I successfully repaired an Audiobahn amp a year or two ago with the help of this forum; hoping I have similar success with this one!

[Perry Babin]

If it has the attached driver board and there are no defective output transistors (either broken legs or shorted), the two transistors in the rectangle are likely defective.

[adelphia83]

Yes, it does have that driver board you pictured.

Upon closer inspection, R207 is burned up, it's near the output transistor Q203. That's the only damage I can find; does this help pinpoint the failure? I'll begin testing output transistors tomorrow, do I have to remove the transistor from the PCB, and how do the "clips" come off that hold the transistor to the heatsink?

[Perry Babin]

Jl audio 500/1 Transistor clamps

For that resistor to burn, the FET would have to be defective. If it's defective, you should replace all of the output transistors on that side of the amp. The two transistors on the driver board should be replaced also. They run hot and tend to fail.

[adelphia83]

What would be the most likely cause of this failure?

I have no experience replacing those small surface mount transistors. Can you offer tips on how this is done?

Also, do you know off hand the part numbers I'll need-- Output transistors, and for those two surface mount transistors?

[Perry Babin]

I posted a link for the clips.

Get the number off of the face of the outputs.

MMBTA42

Apply enough solder to bridge between the legs. Heat the solder and lift the transistor to about 45°. Desolder the bridge between the legs and the board with desoldering braid. Heat the other leg and remove the transistor.

[adelphia83]

Thanks for the link. I'm still uncertain exactly how to get those clips off. Pry them off with the ground-down screw driver? The cotter key tool is pictured, but I'm not sure its purpose.

Does the PCB need to be removed completely from the chassis? That looks like it's going to be quite a process...

[brandes.cm]

The clips remove quite easily if you use the ground screwdriver. Insert the screwdriver and press down towards the pcb. You may find a screwdriver that doesn't need to be ground, but I made one from a larger than needed just for leverage.

Putting them back just align and tap into place using the nut driver pictured at the bottom.