Zener diode in PS1 PSU

Hey guys, Fixing a friends PS1 as it had a ringing power supply and was smoking. I have found that one of the zeners on the output was shorted i have removed it and powered it up and the psu now works but i need to replace it. Does anyone know what the voltage of the zener is? Its listed a d103 / MAZ9120D0LS0-TX/L on the schematic and on page 21 of this manual

Hey there,
Searching for it for a bit lead me to the conclusion that the model of the diode is MAZ9120D0LSO (O at instead of a zero), manufactured by Panasonic. D103 is just that it’s diode number 103 in the schematics, or at least that what it’s named. The diode is a bidirectional TVS diode, packaged in a SOT23 package.
Looking at the schematics you linked, I suspect that the SCK line is a clock line for a communication bus between the CPU and some peripheral. The working voltage seems to be mostly 3,3 V in the circuit. So the breakdown or clipping voltage of the TVS should be in the high single digit or very low two digit volts range. Searching further on multiple sites I found the following: Clipping voltage 12 V, rated power 200 mW.

So it should be replacable by and bidirectional TVS in a SOT23 package with a clipping voltage of 12 V and a rated power of 200 mW. Shouldn’t be too hard to find. Just make sure that the direction of the diodes inside the IC matches that of the original. Shouldn’t be a problem to find out from the schematic and layout in the file you linked :slight_smile: