If you want the best possible RGB output from your CRT and don't want to try various resistor values and build blanking divider circuits, then this RGB tuner is for you. I mean who wants to sweat over an RGB mod? 😃
Some CRTs don't give the best possible RGB output with the calculated values. With some chroma chips R, G, B inputs only go through cutoff adjustments. This is where it is nice to have an apparatus to fine tune the injected RGB signal.
Also, it's nice to have a device to test various RGB resistance values, especially if the chroma chip blanks at weird voltages.(i.e. 2.5V).
How does it work?
It's fairly simple. There are 7 adjustable pots on the device.
If you look at the above impage, there are:
- 3 pots to adjust the RGB termination resistance values (75Ω to 1 kΩ)
- 3 pots to adjust the RGB inline resistance values (75Ω to 10 kΩ)
- 1 pot to adjust the blanking resistor value (this will help vary the voltage upto 5V)
For termination resistance, the minimum value is set to 75Ω. You can adjust the termination resistance from 75Ω upto 1000Ω. While most mods would utilize 75Ω termination resistance, there are some RGB mods that will look better with 180Ω to 200Ω termination resistance (Example: Samsung TXH 1973).
There are pads around the board that act as test points. This is a great way to measure and set the resistance of the pots and the voltage delivered through the ribbon cable.
For the RGB inline resistance values, you can adjust it from (75Ω to 1 kΩ). Adjustments are going to really fine with this range.
For the blanking resistance, you can adjust the resistance from (0Ω to 10 kΩ). At 0Ω, it's basically delivering 4.3V to the jungle chip. (5V - 0.7V from the diode)
This board doesn't have an option to include exclude in-line capacitors. For example, in some CRTs you would need 3x 0.1uF caps or 3x 0.47uF ceramic caps to be included inline before feeding the RGB signal to the chroma chip. However, for mods that require these caps (i.e. BA-1), you really have nothing to tune.
Can I buy this?
This is the first revision of the board. It's available in extremely limited quantities for those who mod frequently. This is to be priced at $40 + shipping.
Only way to order right now is to contact me and check for availablity at firstname.lastname@example.org