PAL 1-Chip Super Nintendo RGB output too bright

[paulb_nl]

I recently bought a PAL SNES 1-Chip and I have noticed that the RGB output is too bright. The 3 brightest white colors on the gray ramp from the 240p test suite are just one color. On my PAL multichip and my US 1-Chip they are 3 distinct colors.

If I measure the resistance of the red, green and blue pin to ground on the scart plug when connected to the SNES I get 49 ohms. I get 75 ohms when the cable is connected to my PAL multichip SNES. This is with an official PAL SNES RGB cable.

Should I change some resistors in the console?

[AndehX]

I believe the NTSC and PAL SNES use different SCART cables. I think one has resistors in the cable and one has capacitors.

[Guspaz]

Was the 1chip already modified with an RGB amp, and maybe they didn't do the brightness mod?

Scroll down near the bottom: http://retrorgb.com/1chiprgb.html

[blizzz]

I've heard that the voltage on PAL 1CHIP consoles is too high. A modder on a German board mentioned that they always fix it when they get a new console, but I don't know how exactly.

Edit:
Found this fix: Replace resistors R15, R16 and R17 with 75 Ohm ones. But don't quote me on that, it's just what I found online.
Edit2: Disregard ^

[borti4938]

I recently bought a PAL SNES 1-Chip and I have noticed that the RGB output is too bright. The 3 brightest white colors on the gray ramp from the 240p test suite are just one color. On my PAL multichip and my US 1-Chip they are 3 distinct colors.

The 1Chip-SNES outputs R-, G- and B-signals, which are above standard. No matter whether it is modded or not.
By standard these signals have 0.7Vpp with matched loads, but the 1Chip-SNES gives 0.8Vpp.

If I measure the resistance of the red, green and blue pin to ground on the scart plug when connected to the SNES I get 49 ohms. I get 75 ohms when the cable is connected to my PAL multichip SNES. This is with an official PAL SNES RGB cable.

The SCART cable of PAL-SNESes has 75 Ohm pull-downs at the R-, G- and B-wires because the PAL-SNES is designed for 39 Ohm load (approx 75 Ohm parallel to 75 Ohm (within the TV).
You get different by just measuring the load to Ground (just the Scart without the TV) because the 3Chip-SNES has a diode prior to the output (that's why you just measure the 75 Ohm), but the 1Chip-SNES has just the 39 Ohm resistors between the S-RGB and the MultiAV. That why you measure the 75 Ohm parallel to some impedance through the S-RGB, which gives you the 49 Ohms.

Just in short: the 1Chip-SNES gives you a brighter image than the 3Chip-SNES by default.

Edit for blizzz: changing the 39 Ohms to 75 Ohms is just to use RGB cables without the additional 75 Ohm loads. This has nothing to do with the brightness.

[paulb_nl]

Was the 1chip already modified with an RGB amp, and maybe they didn't do the brightness mod?

Scroll down near the bottom: http://retrorgb.com/1chiprgb.html

I opened it up and it's unmodded.

Just in short: the 1Chip-SNES gives you a brighter image than the 3Chip-SNES by default.

Edit for blizzz: changing the 39 Ohms to 75 Ohms is just to use RGB cables without the additional 75 Ohm loads. This has nothing to do with the brightness.

Well my unmodded US NTSC 1-Chip shows all the colors from the 240 suite properly (with an NTSC RGB cable) so at least the US 1-Chip is not too bright.

How could I lower the brightness of the PAL 1-Chip?

[borti4938]

Would be interisting to see, what's outputted by the S-CPUN at the R-,G-B-lines and what does the S-RGB make out of it. However, for this you will need an oscilloscope.

Question: Is the brightness at composite video correct? (remind that the cable needs an internal 75 ohm load too)

[paulb_nl]

I have been testing with the OSSC so I can't connect composite to it. Apparently my Sony LCD tv has a higher tolerance for the higher levels because the colors are correct when I connect the RGB cable straight to my tv. The brightness on composite on my tv is good too.

[borti4938]

Maybe it is a good idea to either do the RGB bypass, or to replace R15, R16, R17 (all three are 39 ohm res.) with something around 48,2 ohms. This should correct the brightness for your SNES with the stock PAL RGB cable (keep in mind that load is not 100% matched).

[paulb_nl]

I had already ordered 750 Ohm resistors to try the brightness mod described here: http://retrorgb.com/snes1chip.html#brightness. I just installed the resistors without the amp and the brightness is perfect now.

Strange that this PAL 1-Chip-02 was so much brighter than my NTSC 1-Chip-01.