Old_School_Brad
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- Sep 10, 2024
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I’ve had this old, beautiful, heavy integrated amplifier sitting on the shelf for years. Recently, I had some spare time and decided to give it a try.
The problem: After powering it on, it goes into protection mode after about 10 seconds.
When I flip the power switch: it turns red, stays that way for 5 seconds, turns green, and after 10 seconds, it goes red again (indicating protection mode).
If I turn it off and back on, it stays in protection mode (the relay doesn’t close). But if I leave it off for 1-2 minutes and then turn it on again, it comes out of protection, only to go back into protection after 10 seconds.
The issue persists even with all four 4A fuses removed from the two main transformers (which supply the bridge rectifiers).
All measurements I’ve taken were with the components disconnected from the boards, except for the voltage checks.
- Power packs (Darlington, rebranded SK ST100): Good
- Pre-driver transistors 2SC1628 and 2SA818: Good
- Diodes: Good
- Capacitors on both the protection and amplifier boards: Good
- Rectifier diodes (three sets of four for three transformers): Good
- Voltages from all three transformers: Good
- Fusible resistors: Good
I’m hoping for guidance from someone more experienced to point me in the right direction. I'm surely missing something crucial.
I’ve attached the service manual, though I’m not sure if pdf and uploads work as it should.. -Let me know and I'll upload it elsewhere.