Sinuslive SLA-1500 repair

[Mote]

Ive got this amp on the desk and I still have not really worked on any class D amplifiers so I do not really know what I am doing.
Amp drew current, protect LED was illuminated and something made clicking/screeching noises.

All I could find was a leaking output transistor, I removed it.

Then I tried to power up the amp without one output, 7 others in place. Can the amp work with 1 of 8 outputs missing? Mine did not, protect LED came on, dimmed down a bit and amp started to draw current again but no noises.

I had 25W lamp as a limiter inline with B+. I havent had problems with it considering powering up any other amp, but this is the most powerful amp I have worked on so maybe I should replace the lamp with 50W headlamp?

Another thing is a jumper wire and some resistors soldered on pins of U2 - they dont look like they are from factory, should I be concerned about those?

Or any other suggestions what should I do next?

[Perry Babin]

The amp has low voltage protection which could be triggered during power-up. Clamp all transistors and try powering it up trough an ATC/ATO15 amp fuse (no limiter). Will it power up?

I don't know about the jumper wire.

[amc32]

Small fuse like perry said $ are there and numerical indetions on the bottom of hearsink. Check opti in cicuit should be two in output section of amp, pin 1-2 2.5k pin4-5 14k. Pin 5-6 7-8 should read open

[Mote]

Tried it wihout current limiter, only 15A fuse inline with B+.
At first I thought, it does not work, protection LED went off, power LED did not come on. Power LED had failed, 12V on its pins but it is not illuminated.

So the amp switched on. It produces audio at quite high volumes but there is some distortion in the sound. It may be caused by my setup, or the fact that I dont have one output transistor in circuit.

Also there was 0,44VDC between speaker terminals without any input. When switching amp on there is about 0,2V but it slowly rises to 0,44V.

Photos of how 100Hz sine looks like on the speaker terminals. First photo is 1V/1ms, second one is "close-up" 1V/1us.

[Perry Babin]

What's the DC offset with a speaker connected?

I don't see a problem with the waveform.

[Mote]

DC offset with speaker is 0,28V

[Perry Babin]

That's about normal for these amps.

[Mote]

Do you recommend replacing all outputs, just one or the bank of 4 outputs where the defective transistor was?

[Perry Babin]

At least replace the group of 4 that had the defective transistor. Carefully check the gate resistors to confirm that all are within tolerance.

[Mote]

Replaced group of 4 transistors. Resistor for defective transistor was out of tolerance, replaced that as well. Now amp works like a charm.