Modding JVC TM-A14PN for Component In

[Goopa-Troopa]

Hey Y'all, first post to the forum here.
I'm trying to mod a JVC TM-A14PN for component video in. I found a few units in the E-Waste of my university, so that's why I have a unit with only s-video and composite. This is my first time modding a CRT. I'll link the manuals for both the unit and its jungle IC at the bottom of this post.

I know that most people inject RGB where the OSD gets injected into the video, but it seems that the jungle IC has component inputs natively baked in. I just need to figure out how to inject the component signals at the correct levels and so that they can use the sync signal from the Y component. Here's a block diagram of the jungle IC:


The CRT that I have uses the composite signal inputted into pins 45 and 51 in parallel to get sync and luma out of it, and also gets chroma from it. Those signals then get processed so that the pins 37-35 output YPbPr which the unit then feeds back into the IC with pins 31,33, and 34. The test circuit in the manual:


So, what I was thinking was to pass the Y through the sync and Y1 pins, similar to the s-Video input and keep the Y.out pin wired to the Y2 in pin, but inject the Pb and Pr signals into pins 33 and 34 as per the example circuit. Does anyone with better analog IC understanding this this would work? I have an electrical engineering degree but squarely on the signal processing side, so this stuff is black magic to me.

Jungle IC: https://drive.google.com/file/d/1WZQFMJ ... sp=sharing
CRT: https://drive.google.com/file/d/1MGyX7g ... sp=sharing

Thanks for any assistance,
Goop

[NewSchoolBoxer]

I want to preface by saying I don't do mods but my electrical knowledge in the analog space is relatively good and I follow the mod scene because I think it's electrically interesting. I also have a BSEE which means we have very strong fundamentals but we don't know it all.

Yeah I think this will work. You need the 75 ohm termination as you see in the example circuit. Use 1% resistors. The idea is to drop the typically high input impedance to 75 ohm to prevent reflections. The 0.1uF AC coupling capacitors are extremely common. I've seen 0.47uF less commonly but the idea is to remove any DC offset, provide some amount of electrical isolation between signal generator and television without high pass filtering into the low MHz range of analog video. You don't have to have them but better to put them in to be safe unless you get bad black level field tilt. I think everyone uses ceramic but film would be better if you pay the price since it's not microphonic and more linear.

[Goopa-Troopa]

I want to preface by saying I don't do mods but my electrical knowledge in the analog space is relatively good and I follow the mod scene because I think it's electrically interesting. I also have a BSEE which means we have very strong fundamentals but we don't know it all.

Yeah I think this will work. You need the 75 ohm termination as you see in the example circuit. Use 1% resistors. The idea is to drop the typically high input impedance to 75 ohm to prevent reflections. The 0.1uF AC coupling capacitors are extremely common. I've seen 0.47uF less commonly but the idea is to remove any DC offset, provide some amount of electrical isolation between signal generator and television without high pass filtering into the low MHz range of analog video. You don't have to have them but better to put them in to be safe unless you get bad black level field tilt. I think everyone uses ceramic but film would be better if you pay the price since it's not microphonic and more linear.

Thanks for the advice! Yeah I think you're right about the capacitor and resistor from what I remember from my circuits class a couple years back. I just used the caps that were soldered onto the board, but for whatever reason wasn't able to get it to work. I wasn't getting any color from the screen with the mod. I could've just done something wrong though. Maybe I'll try again when I have more time. Fortunately I was able to revert the screen to its original operation though!

[Silverymoon]

I shouldnt work after the mod because the inputs and outputs are also likely enabled and disabled via the I2C bus. You can see the bus at pins SCL (9) and SDA (10). You need to intercept the communication from the CPU and update the right registers yourself. Then you could get a perfect picture.

This mod https://immerhax.com/?p=185 will show you how to interrupt the I2C data and update the registers for the jungle IC TB1226EN. You can copy values for the standard settings, to the correct registers for component and thus use the normal TV menu for this input.

The same issues were found with the RGB mod. The cpu would disable RGB over the I2C bus by updating the registers on the jungle IC constantly and doing the wiring mod would fail to display the correct picture. The website linked shows you how to work around this issue and program the registers on the jungle IC. This mod would be a good starting point for yours and could help you get component working.