[Solved] What Does the ZD3 Marking Signify on Marshall Stanmore Speakers?

what is the marking of ZD3 on Marshall stanmore

Hi,
markings suggest me that they are shottkey diode, if they are really zener diode how they are connected looks a bit interesting.
Pin 7 is a power supply here zener diode make sens, but scheme looks strange, ZD3 should be to base and resistro is between base nad collector. This diode should be <36V while this is the limit for the microchip.
ZD1 make no sens, if this is zener diode it limit/reduce the potential on FB pin, but it not make sens while pin 1 is on GND. Shottkey diode seems more logical but are you sure about connection? My guess is to protect the transistor in optocoupler.
D4 seems to be switching/fast diode.
Regards

https://www.mikrocontroller.net/attachment/59...360_Schaltplan-Skizze_Marshall_Stanmore-2.jpg

the problem was different