Archive for October, 2020

RGB modding the JVC TM-H140PN

Sunday, October 18th, 2020

This is somewhat of a “short” post as I haven’t done the mod myself, but it has been verified that my software also works on this monitor. It’s mainly to index that it is possible to RGB mod it, using the I2C interception method as I’ve described for several other JVC monitors. Pictures and schematics should be credited to Victor Clausson.

The mod is somewhat closer to the DT-V100CG mod than the TM-A140PN one, as the jungle of the TM-H140PN is a TA1276AN and not a TB1226EN as the TM-A140PN uses. This means the software for the Arduino to be used, should be this: https://github.com/skumlos/ta1276an-i2c-bridge

Now just as with the other mods, the jungle needs to be isolated, and the Arduino put in-between the monitors microcontroller and the jungle (refer to some of the other articles if you want to know more). To isolate the jungle we need to remove resistor R540 (SCL) and R541 (SDA). The pads connecting to the jungle should then be connected to the Arduino on pin D5 (SCL) from R540 and D4 (SDA) from R541. The pads going to the MCU (so the other “side” of the footprint) should then be connected to the Arduino A5 pin (SCL) from R540, and A4 (SDA) from R541. On all 4 lines, a 100 Ohm in-line resistors should be added. On the jungle from pin 27 (SDA) and pin 28 (SCL) a pull-up resistor to 5V should be added to each. Usually I’d use 2.7K for these. Power to the Arduino can be taken from CN002 pin 8 and 9, which should be fed to VIN/RAW of the Arduino. Using a 5V rail connected to the 5V pin on the Arduino, can result in a monitor that won’t start. My guess is this depends on how fast the 5V rail comes up.

An example of the hookup. Power supply to the Arduino is still missing. Credit Victor Clausson.

To add RGB, we need to connect to TA1276AN pin 35 (R), 34 (G), 33 (B). Capacitor C519, C518, C517 needs to be removed, and each color line should include the “standard” 0.1 uF in-line capacitor and a voltage divider, like this:

RGB input line attenuation and DC bias circuit.

Now the above picture is actually not the best circuit, as it attenuates the signals more than necessary, and the resulting termination resistance for the lines is 105 Ohm (30+75) instead of the correct value of 75 Ohm. The thing is that the TA1276AN takes 0.5Vpp signals instead of the normal 0.7Vpp, so the voltage divider accounts for this. Many suggest (including myself on earlier posts) using R1 = 24 Ohm and R2 = 51 Ohm, as that creates ~0.5Vpp from 0.7Vpp and 75 Ohm termination, however I’ve begun using R1 = 10 Ohm and R2 = 64.9 Ohm, as this gives ~0.6Vpp which is stated as the maximum input for TA1276AN (I’ve tried direct 0.7Vpp also which works fine, but better go by the specs). This results in a brighter picture, but I’d rather turn down brightness on the monitor, than not being able to turn it up. Your milage and wishes may vary.

Sync should be connected directly to the input pin on either input A or B (on the PCB side of the BNC plug). Which you select will then decide which input should be selected for RGB.

To be able to blank (switch to RGB) you need to lift pin 32 of the jungle, and add a pull-down resistor from this to GND. I usually use 10K here, but the schematics from Victor says 51K. Use whatever 10K+ resistor you got. Now on pin 32, when ~0.75V or higher is applied it switches to RGB. You can use a switch for this, or use pin 16 from SCART, whatever you fancy.

That’s basically it. Check the full schematics from Victor here:

Credit to Victor Clausson