K8044 problem: two channels malfunctioning

On my velleman k8044 two channels aren’ functioning properly.
My lights on channel 1 and channel 8 dim when they’re activated end shine at full brightness when turned off…
But the LED’s on the kit itself go on and off like they should.

Does anyone know what the problem might be?

Check solderings and if necessary, replace the transistors for that output.

I had already checked the solderings and redone a lot of them, to no avail.
But I just replaced one of the transistors from channel 8 (I still had a transistor like that lying around) and channel 8 is working perfect now.

I’ll replace the transistor(s) from channel 1 too when I’ve been to the store.

I replaced the same transistor in the second malfunctioning channel and everything is working perfect now.