Hifonix BRZ1200.1D issue

[mbates14]

This one has a weird issue that I cant pin down.

It works, but it has really low volume. I have to turn the gain all the way up before it begins to beat the subs. Then when I do this, it starts clipping only at certain frequencies, and when this occures it starts cooking the sub, B+ rails drop during clipping.

Idle no clipping I have +/-65V rails. they sag to about 30v when clipping. And its burning the sub when it clips.

 

[mbates14]

Quick measurements gave me this:

100Hz Sinewave tone into RCAs. 0.4VAC input on RCAs.

R201 couples the pre-amp/crossover stage to the Class D driver board. the Driver board side with gain turned all the way up is 0.8VAC.

Pre-amp side of resistor is about 6.5VAC. Resistor measures fine.

is this normal? or is the class D driver bad. Both 8 pin SOIC-W ICs are scratched off. Both get really hot.

any ideas?

 

[mbates14]

I see......

Anyway, I figured out the 2 ICs on the driver PCB are TL072. I have an O2 audio which is a hifonix PCB and it wasnt scratched off.

Replaced them and the issue seemed to have gone away. We will see.

 

[Perry Babin]

When you repair these amps, replace the two 1D transistors in the center of the board, even if they're not defective. They run hot and commonly fail.

 

[mbates14]

Center of which board? also what package, SOT-23?

 

[Perry Babin]

See attached.

 

[mbates14]

Yea, I changed the 2 072s on that board. The top right one looked brown where it had gotten hot, and was getting hot. Changing those 2 op-amps improved the sound.

I didnt change those transistors yet. What is the symptom of these failed transistors?

 

[seankane]

Amp stays in protect.