This powered speaker has some hiss that reveals that power amp is working, but OL (Overload) is always on.
Power supply has -15V but not +15V. No shorts in preamp part. Even disconnecting +15V line, it doesn't show up.
Line regulation is only a BZX55C15 15V zener and a S8050 TO-92 NPN. Zener seems OK, but transistor is not conducting (not shorted though).
I replace it and it works, but... the transistor gets hot as hell. It's 500mA rated. I decide to change it with a much powerful SS8050. It gets hot too, but it'll stand longer. -15V regulator (S8550) gets hot too, but not so much. +5V for DSP (a large IC!) is produced from +15V via linear regulator. Perhaps that's why +15V has extra load while -15V is not so stressed.
Anyway, everything else looks pretty new, so it seems that someone designed this PSU cheaply. Today I've received another Thump15 for repair, same symptom. I'll report if it's the same case. If so, it will be clearly a design quality issue.
Power supply has -15V but not +15V. No shorts in preamp part. Even disconnecting +15V line, it doesn't show up.
Line regulation is only a BZX55C15 15V zener and a S8050 TO-92 NPN. Zener seems OK, but transistor is not conducting (not shorted though).
I replace it and it works, but... the transistor gets hot as hell. It's 500mA rated. I decide to change it with a much powerful SS8050. It gets hot too, but it'll stand longer. -15V regulator (S8550) gets hot too, but not so much. +5V for DSP (a large IC!) is produced from +15V via linear regulator. Perhaps that's why +15V has extra load while -15V is not so stressed.
Anyway, everything else looks pretty new, so it seems that someone designed this PSU cheaply. Today I've received another Thump15 for repair, same symptom. I'll report if it's the same case. If so, it will be clearly a design quality issue.
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