Damaged Zener - speculation on why?
I have one of these AudioSource AMP THREE amplifiers that won't come out of speaker protection. I've traced the protection circuit back to the Zener at D14 where it only measures 2v. This is a link to the schematic.
Looking closely at the diode, it's definitely damaged; it measures open in either direction and there's a little blob of solder on one end and that end looks burnt. When I short across it, the protection circuit deactivates and I get good output. (I checked the rest of the amplification stage to make sure there wasn't something actually wrong there... everything measures normally as best I can tell.)
Any ideas about why this Zener failed? The circuit is pretty straightforward; It gets voltage from a bridge rectifier (measures good) and is current limited by a 220k resistor (R103) which should be plenty. Downstream of that diode is just switching transistors for LED's and relays, very low current stuff.
I don't want to get down the road and have to replace this diode again; is there anything else in this circuit I should replace or check while I'm in there? I did remove and test C17, thinking that cap had an issue but it measured fine.
Just looking for some advice from folks more experienced than I. Thanks in advance!