sinuslive sla1500 protect

[yoppi]

Hi



I am repairing a SinusLive SLA1500. I arrive with the output in shorted. I replaced all 640n.
The amplifier turns on well and sounds good at low volume or minimum gain.
The problem is when I raise gain, the amplifier goes into protection. It does not matter if the load is connected or not, it enters protection in the same way.
Could it be that the drive board is in poor condition?

 

[Perry Babin]

Do you still need help with this?

 

[yoppi]

Yes, I have not been able to solve the problem yet

 

[Perry Babin]

You stated that the amp goes into protect when you raise the gain. Does it go into protect if the gain is set at the minimum and the input signal is increased?

Does the output signal remain clean up to shutting down?

 

[yoppi]

no, if the gain potentiometer is at the minimum and the input signal is increased, it does not enter protection.
yes, the amplifier sounds perfectly until it goes into protection



it does not matter whether it has a load or not connected at the output, it also protects

 

[Perry Babin]

Do you see excessive DC or distortion as the gain is increased?

 

[yoppi]

It has nothing of DC in output. the distortion does not appear before it is protected. I have also injected a tone of 50hz and in the output, the wave in the oscilloscope is totally clean

 

[Perry Babin]

The brown fixative on the board has become conductive. That could be part of the problem.

Do you see an unexpected change in the input signal to the driver board as the gain is increased?

 

[yoppi]

I already cleaned and restored the area of drive board that silicone brown.
The 90º pin that connects the drive board with the main board is new
no, the gain increase is progressive, without frights until it protects

 

[Perry Babin]

Lift Q50. Does that stop it from going into protect?

If not, solder it back down and do the same with Q23.

Be careful, this will disable part of the protection circuit.

 

[yoppi]

I have removed q50 and it works perfectly

 

[Perry Babin]

If you haven't done so, clean up all of the fixative from the area of Q48-Q50 and around RP1. Reinstall Q50 if it's good and re-check the amp.

 

[yoppi]

Hi

It seems that the problem has been solved. after cleaning ...
Do you know what function RP1 has?

 

[Perry Babin]

http://www.bcae1.com/temp/SLA1500.pdf

If it's the same as RT1 in the diagram above, I think it sets the bias point/threshold for the protection circuit. I don't have any information for what it's to be set to.

 

[yoppi]

Ok, thanks Perry