Hi, I'm repairing a Rogers A100, but I can't figure out the potection circuit.
It had Q1, Q2 and Q3 fried, D9 diode and zener diode failed too. I have replaced them, but it is not working.
The thing is that I removed the transistors and noted the position, but lost the note, and I don't know if the serigraphy in the board is correct.
I don't really understand how this circuit works, so I drew the schematic, since there is no service manual available. Transistor are positioned like the board serigraphy.
Without q1, q2 & q3, relay clicks by q4 that detects AC, and have 21v between coil leads. But when I put the other transistors, relay stays open, having 11v between coil leads.
Rest of the amplifier is working fine now, no DC on outputs, and sounds good.
image link for full size:DSC69982 — imgbb.com
It had Q1, Q2 and Q3 fried, D9 diode and zener diode failed too. I have replaced them, but it is not working.
The thing is that I removed the transistors and noted the position, but lost the note, and I don't know if the serigraphy in the board is correct.
I don't really understand how this circuit works, so I drew the schematic, since there is no service manual available. Transistor are positioned like the board serigraphy.
Without q1, q2 & q3, relay clicks by q4 that detects AC, and have 21v between coil leads. But when I put the other transistors, relay stays open, having 11v between coil leads.
Rest of the amplifier is working fine now, no DC on outputs, and sounds good.
image link for full size:DSC69982 — imgbb.com
Last edited:
Yes you have hit the nail on the head …… they would be BC640 PNP . The relay would normally operate on power up by half wave rectified pulses from the AC supply making Q4 conduct . A DC condition from the speakers would make Q1 conduct causing Q2 and Q3 to also conduct and so short circuit the voltage across the relay causing it to release .
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