In case you’re looking for TM-H140PN look here: https://immerhax.com/?p=558
Note: This guide works for TM-A140PN, TM-A14PN, TM-A13SU and TM-A130SU.
So, a friend of mine got a hold of some JVC TM-A140PNs (and TM-A14PN which is the same, but in plastic casing) which only takes composite and S-Video. So since nobody likes that, we wanted to RGB mod it. Open the sucker up, desolder the large metal shield in the middle of the board, and behold, a TB1226EN jungle IC. Since I now had some experience with the newer TA1276AN, I was somewhat prepared that shit might hit the fan. And of course, it did.
So blanking occurs with pin 22, Analog YS, and since I chose to blank on 5V (from SCART), we need proper pull-down, in order to avoid excessive current drain. So I switched the something like 10 Ohm resistor that pin 22 was grounded with (R726), to a 10K, so when 5V is applied, current draw is minimal, and when not, we still have 0V to allow composite/S-Video as before. After doing this, we could see that we could blank by attaching 5V to the pin and see the screen turns black. After removing C718, C717 and C716 which were the capacitors decoupling RGB pins to ground (as there is a DC offset voltage on these pins, just like the TA1276AN) and then injecting RGB to pin 23 (R), 24 (G) and 25 (B) through the same circuit as with the TA1276AN, we still got black screen when applying video.
So, with previous experience in mind (check the DT-V100CG RGB modding post), I hooked up the Arduino circuit to the I2C lines, by removing R292 and R291 and using that as entry point. R292 is the SDA line (yellow cable in the pictures), and R291 is SCL (green cable). On each line there’s also 100 Ohm resistors in-line (as in series), both on the incoming I2C and on the “new” I2C bus (they’re the resistors inside the black shrink tube). The side closest to the jungle IC was connected to the “new” I2C bus created with the SoftI2CMaster library, and the other to the hardware I2C/TWI. Firing up the screen, it didn’t boot at all. I could see it was communicating, but it never initialized properly. It seems that it is really sensitive to timing, and at the same time, the monitor software is *constantly* refreshing *every* single goddamn register in the jungle IC. So I had to rearrange the code which was somewhat trial and error, until I had something that could start.
Anyway, after doing that, I could see that the monitor software wrote 0h to register 06h, which is the RGB contrast register. Yay! Thanks for killing the RGB image! Anyway, some I2C packet mangling, and were good again. Basically, when the monitor writes to register 06h we ignore it, and when it writes to 00h we replicate that to 06h.
At the same time, I ensured that it would never mute RGB in register 1Bh, if for some reason it would think of doing that. Contrast setting on the OSD will now also work, as data is replicated to RGB contrast register. Sync was attached to line B at the board on the pin, so it is properly routed to the sync and Y pins of the jungle. Audio from SCART was merged to mono, by the below circuit and then soldered to the RCA input pin inside the monitor.
I then 3D printed a small “case” to put SCART on the back of the monitor, with RCAs to send audio out, and then a switch to switch between the RCAs and sending audio to internal mono shitty speaker.
Find the code for the Arduino here: https://github.com/skumlos/tb1226en-i2c-bridge
So there you have it!