It's a service letter mod requiring the single 32v zener to be replaced with two. A 17v and a 18v.
From a MTF post:
Here is a link that has information in Audiokarma:
http://www.audiokarma.org/forums/showthread.php?p=1182717
I hope these parts numbers from US supplier mouser.com help you find suitable replacements in your area.
these are just for the factory SX-1980
These are all the diodes, both the original part number, and a replacement with identical specifications:
D210 wz-240 >>
512-1N5252B Fairchild 24 V, 0.5W Zener diode 5 percent $0.06
D211 wz-240 >>
512-1N5252B Fairchild 24 V, 0.5W Zener diode 5 percent $0.06
D213 EQA01-35R 35 volt 5 percent 0.5 watt zener diode. replace with two diodes:
D213 >> (#1 of 2)
512-1N5247B Fairchild 17 V, 0.5W Zener diode 5 percent $0.06
D213 >> (#2 of 2)
512-1N5248B Fairchild 18 V, 0.5W Zener diode 5 percent $0.06
OR
D213 >> (#1 of 2)
512-1N4744A Fairchild 15 V, 1W Zener diode 5 percent $0.08
D213 >> (#2 of 2)
512-1N4747A Fairchild 20 V, 1W Zener diode 5 percent $0.08
I'm not sure what EchoWars recommendation is... the 0.5w vs 1w isn't clear
and I didn't find 17v 1w zeners either... so 20+15 is closest
D215 1S2473 >>
512-1N4148 Fairchild Diodes - Small Signal 100V Io/200mA $0.03