Folded Cascode CEN IV with fixed Rails

[baswamin]

Hello Patrick and fran,

I built one board but ran into issue. I had the one of the current mirror pfet orientation incorrect (Q5a/b). When testing this, the output buffer transistors got really hot. Voltage on output was -11V.
Once I corrected the direction of pfet, I quickly checked by turning on the circuit for few seconds and I still see -10V on the output. I am scared to keep the circuit running since it may damage some other component. Any guidance on how to proceed? Is it safe to run the circuit for debugging?

Thanks

 

[baswamin]

Ok, I have found the issue.

Q8 is supposed to be K170 but I see it is J74. Basically, the quad K170 I bought from diyaudio store had sent one of the transistors in Quad K170 as J74. For a moment, I thought I might have soldered from nnpp set but that set still has k170 and j74. So, I will build the other board and check and will contact the store and check about replacement.

Moral - read and confirm the components before soldering.

Thanks

 

[EUVL]

Most likely some other transistors are damaged.
You need to remove them all and test one by one.
Either will a transistor tester, or many information on the internet.

And you should be using lab supplies with current limit set to ~30mA.


Patrick

 

[baswamin]

Here is the pic

 

[baswamin]

Most likely some other transistors are damaged.
You need to remove them all and test one by one.
Either will a transistor tester, or many information on the internet.

And you should be using lab supplies with current limit set to ~30mA.


Patrick

Hello Patrick,

It is almost impossible to desolder the components correctly. I will try first with replacement k170. It will take lot of time to procure. If it does not work, then not sure what to do. For now, let me build the second board and check.

Thanks