Taramps HD8k low volume output

[barber02]

I have a Taramps HD 8000 on the bench that has significant ringing on one side of the output transistors, and uneven voltage on the speaker terminals. I’m thinking the the higher voltage present on the positive terminal is be induced by the ringing. I tried wiggling the output inductors for both sides and it didn’t affect anything.

I’m getting 176 volts rail on both sides, but I’m suppose to get half rail voltage at the speaker terminals. I get 88 volts on the negative terminal and 96 volts on the positive side. I see these same voltages at the output mosfets as well.

I am attaching screen shots of the drives on each side.
Scope settings are 5v 10us probe is set to x10.

Has anyone seen this before? Suggestions?

David.

 

[barber02]

Here is a picture of the output section.

David

 

[miniman82]

Looks to me like the negative going half of the wave is the one ringing in the first picture, are any of the FETs leaky or is the driver IC not fully pulling the gates down? Out of tolerance gate resistors? You can see that the ringing is diminishing in amplitude as time goes on which means it's switching off, but not off enough to damp out the oscillation. I'd suspect a slightly high resistance in the gate circuit, leaky FETs or a bad driver chip.

 

[barber02]

Thanks miniman82 for your suggestions. I checked all of the resistors around the FETs and the driver ICs on both sides after I created this thread. Nome of them were out of tolerance. I’ll pull the FETs and test them out of circuit and if they are okay then I’ll replace the driver ICs one at a time and see what happens.

 

[barber02]

The issue was a bad gate driver IC. I replaced it first because I didn’t have to disassemble the amp to do it. That resolved the issue.

Thanks for the help,

David

 

[ultra]

David, you ve got gmail

 

[barber02]

Thanks Ultra