Damaged the STM32

[aiyiadam]

I have just fried the STM32, while I was testing a digital amp. The amp had an output of ~5Vpk (600Hz sine wave) and was connected to a 8 ohm speaker. I connected the probe to the positive and the ground to the negative output of the amp, which was a mistake big enough to destroy the oscilloscope immediately. It was a mistake but I was still a bit surprised.

I am just not very used to working with oscilloscopes and realize that it is not okay to treat them like multimeters.

However, I am planning to order another DSO Shell from Banggood and have a question: Would I damage the DSO Shell(with voltages up to 35Vpk) during testing, if I connect the ground to the negative lead of the digital amps power supply?

Testing the signal shape of amp outputs (fed by a sine wave up to 100w) will be the most extreme thing, which I will do with an oscilloscope.

[aiyiadam]

Let me also add a photo of my genuine DSO Shell and ask one more question: What is the DC rating for the C1?

Thanks

[jye1]

Did you use a power supply that shared the same ground with the amplifier? If ground is isolated 35Vpk signal shouldn't damage the scope.

C1 is rated at 50V DC.

[aiyiadam]

Thank you for the reply.

It is a cheap TDA7492 amp board powered with a 4.74A Delta Electronics brick power supply. The negative of the power supply is referenced to the ground. And I was powering the DSO Shell with a powerbank (using a 9V step up USB cable).

I forgot to mention the very important point that I had bridged the outputs of the amp. The negative amp output was active and grounding with this output would probably damage any scope. People use differential probes for this.

If I use the amp ground (negative of the power supply) for the DSO, I could just test the amp outputs separately?

And regarding the C1: Could I use a 100n polyester cap with higher DC rating for C1?