NAD 317 Burnt Diode on inputboard

[Cowdangerous]

Hello all,

I bought a NAD 317 recently and i opened it up for a visual inspection. Here i found Diode 657 and 658 on the inputboard, looking like they are burnt. So i traced them in de service manual to what i think is the input protection? I am a newby in electronic repairs but i would like to make it a hobby. Can anyone help me with what this is, where it is for and what i need to replace? Is there anything else i should check while i replace these diodes?

The amp is working fine so far and i think it sounds great. I've tested it with my turntable (which sounded really bass heavy), bluetooth and direct connection on my phone.

Thanks in advance!

[Gyro]

Welcome.

Those are series Zener diodes to drop those +/- 52V rails down to something that the 24V regulators can safely digest. They most likely run warm, they look fine. As long as they don't read dead short then they are fine (if they were shorted, the regulators would have blown up by now).

[Cowdangerous]

Hi,

Thank you very much for your reply! They indeed do run warm! Measured around 50 degrees Celsius while the rest stayed around 30.

[Gyro]

Yes, they're fine then. They're perfectly happy at 50'C.