Hifonics Brutus BRZ1200.1D

[Don Hathcock]

That may be possible. I have been using the AudioQ schematic for a reference but there are several differences.
If I let my DMM probe touch pins 6 and 7 at the same time it reads 14.34vdc.

 

[Don Hathcock]

I remember finding this op amp voltage when I originally was checking it. I have been working on this one on and off for about 3 months or more. I suspected it then. In fact I ordered 4558 op amps just in case.

 

[Perry Babin]

If you're going to replace it (there are more tests that could be done before), look for traces on both sides of the board for pins 5, 6 and 7.

 

[Don Hathcock]

I will. I will pull it out of the heat sink in the morning and check.

 

[Don Hathcock]

Pins 5, 6 and 7 do not have any traces or connections. I have not replaced that IC.

 

[Perry Babin]

The noise shouldn't be audible in the other channel of that op-amp but there could be some crosstalk into the other channel. I'd suggest shorting pins 6 and 7 together and connecting pin 5 to either the secondary ground or any non-PS terminal of the other channel of the op-amp. This will keep it quiet.

 

[Don Hathcock]

So connect pin 5 to either pins 1, 2 or 3?

 

[Perry Babin]

Yes. When you do, pin 1/2 should follow whatever signal is on the pin that you connect it to.

 

[Don Hathcock]

Connected it to my small power supply with a 2A limit and connected a 15" woofer with no input signal. It maxed out the current, so I increased the current limit to 5A. It still has the static noise through the woofer without an input signal. It was drawing ~4.5A.

 

[Perry Babin]

Is that op-amp now quiet?

 

[Don Hathcock]

No. And I can also hear a hum and a kind of higher pitched whir in the background of the static. The whir sound is like the sound you get sometimes tuning in an older radio.

 

[Don Hathcock]

I was checking the other op amps DC voltages. I disconnected the woofer. The only op amp with a board designation is IC6. I found -13.73vdc on pin 1.

 

[Perry Babin]

Are you saying that the output of the unused op-amp still looks like the waveform you posted?

Does the noise you hear sound like this:
http://www.bcae1.com/temp/cooleditmixedoscillator01.wav
What's the DC voltage on the pins of IC6?

 

[Don Hathcock]

Attached screen shot of pin 7 of the op amp that I shorted pins 6 and 7 together. Pin 5 connected to pin 1.
Yes, the noise sounds exactly like that.
DC voltages of IC6:
Pin 1) -13.73
Pin 2) -.026
Pin 3) -.027
Pin 4) -15.11
Pin 5) 0
Pin 6) -.001
Pin 7) -.001
Pin 8) 14.84

 

[Perry Babin]

That sound is due to unsynchronized oscillators (PS and output). There isn't anything practical to stop it.

If pin 5 is connected to pin 1, why don't they have the same voltage?

 

[Don Hathcock]

The voltages listed above are from IC6. The one that I shorted pin 6 to pin 7 and connected pin 5 to pin 1 is a different op amp. The voltages on it before the connection changes is listed above in item #39. The voltages on pins 1 and 5 on it are the same now.

 

[Perry Babin]

For the shorted op-amp, does pin 7 look the same as pin 5?

I don't know how the op-amp IC6 is being used. The fact that pins 2 and 3 are the same, seems to indicate that the op-amp is doing its job but the voltage on the output pin is odd, being so close to the supply voltage. From the numbers alone, I can't make any definitive conclusions.

If you short pins 1 and 2, does the voltage on pins 1/2 match the voltage on pin 3?

 

[Don Hathcock]

For the shorted op-amp, pin 7 looks the same as pin 5.
On IC6, I shorted pins 1 and 2.
The voltage on pins 1/2 are -13.77 and the voltage on pin 3 is -.005.

 

[Perry Babin]

That looks like a defective op-amp unless something external is driving voltage to pin 1. When pins 1 and 2 are shorted, the op-amp is a follower and pins 1 ans 2 should match 3.

 

[Don Hathcock]

I don't have any TL072 DIP8s. I have them on order. Can I use a 4558 just to check it? And should I replace the op amp that I shorted earlier?