I know this is not about computer stuff but it's still retro-gaming related and there's a few people with CRT knowledge here, so:

Recently I got for free a cheap chinese-branded 21in CRT TV to use with my game consoles. Cool thing about it is that it is relatively new (2010 or so) and the Samsung tube in it seems to be as good as new, it also supports component input so that covers most of my needs, not looking to pay absurd prices for a high-end Sony set or anything like that.

Now, the back panel has a round area labeled "S-Video" but the corresponding hole with the connector is not open, so it's likely used for models that do have S-Video input. I opened the TV and by looking at the board there is indeed a footprint for an unpopulated S-Video connector, so I was interested in adding that input as it is much easier (and cheaper!) than getting component out for most consoles with a very similar level of quality, especially on an old CRT TV.

Obviously I need to populate the S-Video connector, which is very easy to do, but there may be other things missing in the circuit that were not included due to cost-cutting. Luckily I found both the schematics for my generic chinese board and the datasheet of the jungle chip (even though it's all in chinese):

So, from what I can tell by using auto-translation the jungle chip uses pins 23 and 24 as multi-purpose inputs for both composite and S-Video, with 23 being the first CVBS input / chroma in and 24 is the second CVBS input / luma in. It also mentions on page 13 something about being able to set pin 23 as either chroma in or CVBS via the service menu, as well as setting some A/V switches (pin 56). But if someone knows chinese and can translate more accurately I'd be grateful.

By comparing the schematic with my own board, I can see that each composite input is connected to one of the S-Video inputs as indicated in the datasheet. From there, on each of the inputs we have the 75ohm termination resistor as well as an electrolytic cap + 100ohm resistor in series that goes straight into the corresponding jungle chip input (pins 23 and 24). So far so good! However, in the schematic there is a zener diode (part number W05Z15C) connected from ground to the input, these diodes on each of the 2 video inputs are unpopulated in my board. What is the purpose of these, are they necessary for the S-Video input? Also, based on the part name I'd assume they are 15V zeners, does that sound correct? No datasheet can be found for this part name unfortunately.

Thanks for your help!