Identitying Zener Diodes on Futaba VFD from Advantest R3752B Network Analyzer

[Ondre]

Hi!
I'm currently repairing an Advantest R3752B Network Analyzer which has a bad PSU and a bad frontpanel display. The power supply is almost fixed - just a bunch of dry caps.
The VFD, as you can see on the picture, had a bit of a rough time. The board is supplied with 5V for the logic and 12V for the HV supply.
Since R48 and R49 were burnt completely, I replaced them temporarily, connected the power (with limited current on the 12V line) and they immediately started smoking again as I increased the current. So I figured that the two nearby driver ICs were probably toastet. I've bought a few SN755701FTs from a dubious source on Amazon and replaced them as well. Current drawn on the 12V line is now approx. 2A. The two driver ICs are getting a bit hit and the display is still dark. I examined the HV supply a bit and found two z-diodes (ZD1 and ZD3) that were shorted and one (ZD4) that has an implausible voltage.

Here's where I need a bit of your help. I have no idea what value z-diodes are supposed to be used here.
ZD3 has a color code (yellow, yellow, green) which I couldn't find anywhere. 
ZD1 is probably 9.3V, but I'm not sure.
ZD4 has written 12 on it, but has a zener voltage of about 3.8V. Is that correct?

It would be great if someone could clue me up on how to decode the readings on these diodes.