S-Video addition to smaller (20") Trinitrons (BA-4D)

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matt_c
Posts: 3
Joined: Fri Dec 31, 2021 3:08 am

S-Video addition to smaller (20") Trinitrons (BA-4D)

Post by matt_c »

I just completed my first net new modification a rather lack luster Trinitron I picked up a couple weeks ago (KV-20M42). This TV only came with 2 sets of composite inputs with mono audio, and a RF input.

Given that this chassis shares the following models (KV-20M42,KV-20M42,KV-20S42,KV-20S42,KV-20S43,KV-20S43,KV-21MB42C,KV-21MB42M,KV-21MB42P,KV-21ME42,KV-21ME42C,KV-21SB42C,KV-21SB42M,KV-,1SE42,KV-21SE42C,KV-21SE82,KV-21SE82C), I'm hoping that this information will come in handy to some people here, either for S-Video directly, or for tying into a straight luma signal.

First off, this thread takes quite a bit of information from an already existing thread over here, viewtopic.php?f=6&t=65583, specifically posts by BazookaBen, however, since we are working on a different TV with lines pre-plumbed, auto sensing of the shield connector and a different chassis, I thought this might be best in its own post.

This series of TV's include the KV-21SE82 and KV-21SE82C models. These models seem non existent in the real world, and I can't find for the life of me either an image of the tv on google images or a proper user manual, these TV's seem to have included an S-Video port...... Which means that there is a place for a port on the board, and all lines are pre-plumbed. So, in order to get this port to be fully functioning, we need 3 fully populated lines to be run
- Luma
- Chroma
- S-Video Auto Sensing port (This isn't technically needed, as it could likely be shorted.... but I'll show how to populate it here to get the full functionality of one of the KV-21SE82 and KV-21SE82C models)

There are two primary chips we will need to interface with to make this work

IC301 - C1 and CVBS1/Y1
Image

IC001 - S-Video enablement switch
Image

Luckily for us! The Luma path is already populated as this is currently used for the composite 1 input source.
However, the Chroma path is required for S-Video to work, and this is not populated at all. Fortunately, due to the parts list for the KV-21SE82 and KV-21SE82C, we can derive what these values would have been. Please see the image below for where these go (and remember, a continuity tester is your best friend to make sure the path is complete afterwards)
Image

Now with that done and over with, we get onto the auto switching functionality. This one took me ages to figure out (OK, a few nights, and a ton of thinking for why my S-Video connection wasn't picking up). The way that this works, if I've figured out this circuit well enough is that when fully populated, the board will run (high) 5v constantly to the shielding pin on the S-Video connector, and to the I-SSW switch on the IC001. Thereby, when a grounded S-Video connector is plugged into the unit, the S-Video cable will ground out the 5v Signal, causing the I-SSW to read low, and enable both the luma and chroma inputs on the IC-301. likewise, an unpopulated path will float, and the luma and chroma pins will never be enabled.
Sorry for the poor photograph here, but I've identified all parts, that need to be added in
Image
After saying all this though, I bet that if you just grounded the I-SSW pin, that your video 1 would run in S-Video mode permanently, which would be handy for pulling in a luma signal for RGB mods. (This is not tested, only theorized)

You will notice two ? points in the image above. the 1? refers to a unidentified part, it ties the line directly from the shielding to ground, however, I don't know what should be placed here, likely a resistor or a capacitor. Similarly for point 2? in the diagram, this is likely a capacitor, I just don't know what value would have originally been intended as there isn't proper documentation. If anyone has a similar chassis that they can refer to, please let me know what I can try here.

Alright, after doing the above, you will need to go to service mode and set ID-1 to 19, and disable the CRTP setting to get the TV to recognize the input.

Hopefully this helps someone in the future from re-inventing this wheel. Thanks for all the great info on these boards that helped me put this guide together as well!

--
matt_c
robotvendingmachine
Posts: 29
Joined: Thu Sep 28, 2017 7:55 pm

Re: S-Video addition to smaller (20") Trinitrons (BA-4D)

Post by robotvendingmachine »

This is great info. I am trying to do an S-video mod on my KV-20S20. Looking at the service manual it looks like I need to pull chroma and luma from pins 7 and 9 on the jungle chip. Can you take a quick look and tell me if this is accurate?

https://www.manualslib.com/manual/96015 ... 20m20.html
bigbadboaz
Posts: 1135
Joined: Mon Feb 14, 2005 4:08 am
Location: Los Angeles, CA

Re: S-Video addition to smaller (20") Trinitrons (BA-4D)

Post by bigbadboaz »

Way above my head, but as a lover of both S-video and CRTs, kudos for putting such a detailed summary out here for those who can actually make use of it.
KPackratt2k
Posts: 211
Joined: Sun Apr 04, 2021 11:02 pm
Location: Seattle, WA, USA

Re: S-Video addition to smaller (20") Trinitrons (BA-4D)

Post by KPackratt2k »

I know I'm bumping an almost a year old thread, but since this is related, I thought this would be a fitting addition.

I was able to guide someone into adding S-Video to a Sony KV-27S40 (BA-4 chassis) TV, which is similar to the 27S42, but without S-Video. The mod is similar to this, but some components are marked differently since the larger BA-4 chassis models have different component labels compared to the smaller models.

You must populate the following components:
D250 and D251: Zener diodes (specified as an "RD9.1EW" in the service manual, but any zener diode should work.)
D252: 10V 500mW zener diode
R248 and R269: 1000 (1K) ohm 0805 SMD resistors
R252 and R254: 220 ohm 0805 SMD resistors
R267 and R268: 75 ohm 0805 SMD resistors
R275 and R276: 0 ohm 0805 SMD jumper resistors
R296: 47000 (47K) ohm resistor
C255: 0.047 uF 50V 0805 SMD capacitor
C259: 0.01 uF 50V 0805 SMD capacitor
C304: 0.1 uF 25V 0805 SMD capacitor

There should be pads similar to this on the board where you would connect your S-Video input, specifically the 6 pins above the Composite input (image credit goes to matt):
Image

Measure for continuity from these components to these pads:
Pad leading to R275 and D250: Chroma (S-Video pin 4)
Pad leading to R276 and D251: Luma (marked in the diagram) (S-Video pin 3)
Pad leading to R269 and D252: Sense (marked in the diagram) (Part of S-Video shield or a Switch center pin)
Pads leading to ground (e.g. Tuner shield or RCA jack shields): Ground (S-Video shield and pins 1 and 2. Also to a Switch right pin if using a switch to toggle inputs)

You'll want to connect the relevant pins of the S-Video connector to these vias on the board. If you're using a Mini-DIN connector with the shield divided into two separate pieces, you can wire it for automatic switching by wiring the first part of the shield to Ground and the second part to Sense. Otherwise, wire a SPST switch to those points.

Go into the service menu and adjust the ID-1 setting to 17 (or its current value +16) and save your changes by pressing "Muting" then "Enter" on your remote.
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