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Mote 10th March 2012 05:38 PM

Hifonics Brutus BXi1600D does not power up
4 Attachment(s)
I got this amp to be repaired.
User said that he had problems with amp switching off sometimes, lately it had been happening more often. By switching off he did not mean going into protection but all LEDs go off and amp produces no audio.

I got the amp, at first I did not encounter any problems with it switching itself off.
Although there was this noise in the speaker like someone is searching channels on AM radio. It was quite loud, the Brutus 1100D did not make that loud noises.

Then I opened the amp up, I saw a resistor which had overheated, but still within tolerance and in the center of the board, the big resistors and diodes have got so hot that they have almost unsoldered themselves. After resoldering them I got the result the user described: amp is supposed to be on, no LEDs are lit, they are in working order, I checked. On the center legs of rectifiers I get 58 volts, on opamps there are both positive and negative 15V. Relay does not click.

There are two things which seem to be someones handy work. Resistor across 494s pins and a wire soldered underneath the board. Seen on photos.

What should I check next?

timwebb 10th March 2012 05:54 PM

i have this same amp. it plays fine but sounds like a am radio is playing.

Mote 10th March 2012 05:57 PM

Have you got photos of 494, does yours have the resistor?
Or the blue wire?

timwebb 10th March 2012 06:23 PM

it has the blue wire but not that resistor.

Mote 11th March 2012 11:21 AM

2 Attachment(s)
Resistor on TL494 is connected to one of the timing pins.
I removed it to see what will change.
The waveform on timing caps pin got a little messier thats all. I decided to put it back.

6,2V Zener connected to 4080 was defective, replaced it. Now Power LED is lit red all the time. Pin 3 of 4080 has 7V on it.

Poked around near the relay as well, transistor which is supposed to pull one terminal of relay to ground had 0,7V, 10,4V and 0V on its legs while relay did not engage. When relay engaged then measuring DC with multimeter on its pins would often make the relay to deactivate, also pushing on transistor which I mentioned earlier or other transistors near it would cause the relay to click.
I resoldered their legs and now relay comes on more often than not.

Strange that even that 4080 goes into protection, relay still engages most of the time.

AKHeathen 11th March 2012 12:27 PM

I take it the led switches from green or yellow to red, and the pics are with and without the resistor. I can only assume 0.7v is insufficient gate voltage

What is the transistor that drives the relay ground, and what drives it?

Mote 11th March 2012 12:56 PM

LED is either green or red, or in my case: green, red or does not light up at all.
Transistor which drives the relay to ground is C3228, its base is connected to LM393 opamps output, one of the inputs is connected to the same output via resistor and diode, other input is connected to 6,2V zener and to another opamp.

Yes the pictures were with and without resistor.

Mote 11th March 2012 01:18 PM

There is some intermittent connection somewhere. If I bend the board I can hear a faint click, Power LED turns red, then relay clicks, bend the board other way, LED goes off and relay clicks.
Power supply keeps working all the time. Rectifiers center legs have 58V on them, but now if LED is off there is no more 15V voltage for opamps.

Where to search for broken contact?

Mote 11th March 2012 02:01 PM

Found my intermittent contact. Two of the output transistors had broken legs.
They are the infamous IRF3710 which have to be replaced with IRF3710Z.
I am still very inexperienced with class D amps, I know there are 4 banks of outputs, what are my options for further troubleshooting the amp with the 10 output transistors?

Mote 12th March 2012 09:35 AM

Disregard everything that I have posted so far.
I repair the legs of outputs with solder as a temporary fix to see if that was the problem with the amp. Seems that it was not the only problem.

All the components are in the amplifier, nothing is removed.
Symptoms are:
When remote voltage is applied, red protection LED lights up for a few seconds (as it should) then it goes out, the other LED (two LEDs in one: green and red) does not come on at all. Power supply is working 58V is on rectifiers center legs and on some of the outputs which are directly connected to the rectifiers. Also +/-15V is present on opamps. When I bend the board the second LED (green/red) lights up red because HIP4080 is in protection (3rd pin 7V). After a second relay clicks.

When I release the pressure from the board, sometimes the red LED stays on for a while, so I can take a few measurements, sometimes it goes off immediately after I let go of the board.

What could have a bad contact to cause this?

Could the HIP4080 be bad? I measured voltage on it with black probe on GND terminal (I get the feeling that I should have used RCA shield) and most of the pins had -1V or 7V on them.

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