I found the service manual on the internet. It contains the receiver's schematics.
There is a DC speaker protection circuit, watching each of the 7 amplifier's outputs for DC over a given time period. This circuit disconnects all speakers through relays, and sets the receiver in protection mode (red blink).
There is also a header, normally used for bias pot's trimming, which allows to monitor each amplifier's output before relay. I could see 6 channels settle at 0V a few seconds after turn-on; but the last channel, SBL, would settle at +63VDC.
I sensed the SAP15N and SAP15P of the SBL channel, both were short from collector to emitter. On this site, I found several threads dedicated to blown SAP15's, suggesting to replace them with STD03's. Which I did. It is easy on the 4308 because the SAP15's emitter resistors are shorted on the PCB, so there is no need for additional 0.22 Ohm resistors as is the case with Cambridge amplifiers for example.
Fine and dandy, the AVR works again 🙂
Regards,
--
Stéphane
There is a DC speaker protection circuit, watching each of the 7 amplifier's outputs for DC over a given time period. This circuit disconnects all speakers through relays, and sets the receiver in protection mode (red blink).
There is also a header, normally used for bias pot's trimming, which allows to monitor each amplifier's output before relay. I could see 6 channels settle at 0V a few seconds after turn-on; but the last channel, SBL, would settle at +63VDC.
I sensed the SAP15N and SAP15P of the SBL channel, both were short from collector to emitter. On this site, I found several threads dedicated to blown SAP15's, suggesting to replace them with STD03's. Which I did. It is easy on the 4308 because the SAP15's emitter resistors are shorted on the PCB, so there is no need for additional 0.22 Ohm resistors as is the case with Cambridge amplifiers for example.
Fine and dandy, the AVR works again 🙂
Regards,
--
Stéphane