Taramps DS 1200X4 output transistors getting hot and amplifier pulling excess current

[Perry Babin]

What is all of that in the left image? All you should have is the end of the probe and the ground clip that's connected into the slot in the probe.

 

[cush man]

It's a 3ft banana plug to alligator clip to lengthen the ground wire.

 

[Perry Babin]

Why do you need to lengthen the ground wire? The gate and source terminals are 1/4" apart.

 

[cush man]

I'm such an idiot, I thought you were referring to the source ground and not the source pin on the MOSFET.

 

[cush man]

How can I attach it safely?

 

[cush man]

I can confirm it's 10 volts pkpk now. But there's no safe way to attach it the probes ground to the source pin.

 

[Perry Babin]

Do you have any j-hook type clips?

If not, grip a small length of solid wire into the ground clip and use it as a probe instead of a clip.

 

[cush man]

My brother helped me take the pictures...

First pic is high side gate to source second pic is low side gate to source.

 

[cush man]

I'm going to add those to my next purchase list.

 

[cush man]

Can the kapton tape be used as a long-term thermal pad essentially?

 

[Perry Babin]

The scope probes typically come with that type of clip for the probe itself. You can hold the ground to take the photo. You can check the rest without photographing them. If you do photograph any more, set the timebase to display only 3 or 4 cycles. The resolution is too low with so many cycles.

Are these the original part FETs or did some fail?

Has anyone else worked on the amp?

1mil Kapton tape is generally OK for most class D amplifiers.

 

[cush man]

3 or 4 cycles? I've only been using a scope for a few months now so I'm still learning the ropes.

I can confirm these are the original FETs.

Yes someone else was working on it but they didn't get anywhere.

Okay.

The only thing I changed was 4 6800 SMD resistors to 8201.

 

[Perry Babin]

Resistor change?

5 1/2 cycles in the scope image.

 

[cush man]

These and 2 more on the other side...
I changed them because they were significantly lower than the ones in the other amplifiers, so I thought they were passing to much current to the MOSFETs, that was my reasoning.

 

[Perry Babin]

Are the 'other amplifiers' using the same output FETs?

 

[cush man]

They're different, each amplifier have different brand caps or FETs.

 

[cush man]

Resistor change?

5 1/2 cycles in the scope image.

Okay I get it now.

 

[Perry Babin]

Is this your amplifier or are you repairing it for someone else?

Before the amp came to you (before it failed), was it working normally?

With at least 12v feeding the amplifier (no excessive limiting), what is the rail voltage in this amplifier?

 

[cush man]

I'm repairing it for another technician.

I don't know, I was told it's not working. When I tested it, it comes on but no Audio.

With 12.6 volts going in the rail voltage is +/- 40 volts. The input section op-amp voltages is +/- 14.4 volts. The ICs VCC voltage is 11 volts and VCC2 is 10.4 volts. CSD is 10.5 volts and VSS is 5.4 volts and VAA is 5.7 volts.

 

[Perry Babin]

VSS is probably negative.

Does it now have audio?