Well done 
The RCA17556 will be one of the final output devices. Was it short circuit from C to E?
For the sake of keeping things the same I would probably replace both devices in both channels but the Quad can be uniquely susceptible to the actual devices fitted. Modern high speed parts can cause issues with stability.
The RCA17556 will be one of the final output devices. Was it short circuit from C to E?
For the sake of keeping things the same I would probably replace both devices in both channels but the Quad can be uniquely susceptible to the actual devices fitted. Modern high speed parts can cause issues with stability.
Yes it was short from Collector to Emitter. I have ordered up all the parts I think I need to repair.
Have a read at this that I remembered from a while back:
Quad 405-2 Overheating on right channel.
Hope the repair goes OK 🙂
Quad 405-2 Overheating on right channel.
Hope the repair goes OK 🙂
Sorry for the delay but it took a few days to get the bits and bobs that I needed.
The amp that I had already got working I changed all the 3.3K ohm resistors (4) and restored the new bipolar cap C17. I also changed R10 as there was some corrosion. Also replaced both 15V zener diodes. Amp now working fine and refitted.
The other amp with the s/c RCA 17556 I replaced both transistors with MJ15003 but still no joy. So checked again the good pcb against the faulty one and everything looked perfect. So now staring at both pcb and finally I realised there was something that I hadn’t checked, the fuses ! One of them was blown. Amp is now working fine.
I have similarly changed the same components as the other pcb and the amp still works. CPC were short of Zeners and I will replace them in this pcb when I get them though for now it is fitted in the amp and working fine. Can confirm that the MJ15003 works fine with the RCA 40872.
Thanks for all help and suggestion.
The amp that I had already got working I changed all the 3.3K ohm resistors (4) and restored the new bipolar cap C17. I also changed R10 as there was some corrosion. Also replaced both 15V zener diodes. Amp now working fine and refitted.
The other amp with the s/c RCA 17556 I replaced both transistors with MJ15003 but still no joy. So checked again the good pcb against the faulty one and everything looked perfect. So now staring at both pcb and finally I realised there was something that I hadn’t checked, the fuses ! One of them was blown. Amp is now working fine.
I have similarly changed the same components as the other pcb and the amp still works. CPC were short of Zeners and I will replace them in this pcb when I get them though for now it is fitted in the amp and working fine. Can confirm that the MJ15003 works fine with the RCA 40872.
Thanks for all help and suggestion.