[jyt]

Hi wondering if the SK25 is suppose to get hot, I mean real hot, I build 4 and 3 of them get pretty damn hot, the 4th one not at all. I'm talking about the Q9 BD139 NPN power transistor.

Also just to add here, I'm using a test jig, so to not burn anything on the module, the one that is cool, seem to give little more output judging by the reading of the oscilloscope. the other three are similar to each other.

[JPK]

It is supposed to get warm but not hot.
I think you have an issue.
Do you supply them with higher than +/-16V ?
Check if you get any DC voltage on the output. It should not be above a few millivolts.

[jyt]

On my jig i send 15.1 DCV to the Opamp.
I dbl check and redone the soldering on all the opamps and are now perfectly working, was simple, the soldering between the main pcb and both power transformer pcb is crucial. Perhaps there is need to specified this important info in the build document. Anyway it is now all good.

Thank you JP for your quick answer.

[jyt]

1. before fixing the soldering



2. after, the opamp does not get hot at all, stay all cool



3. the fix