I have a Technics SL1200 turntable connected to a Vestax PMC-05 Pro mixer and I send the outs of the mixer into the line-in inputs of the 404sx via RCA cables, for sampling.

My master control volume on my mixer is at about 60% and the input level on the 404sx is at 127, but the peak light doesn't light up. Also, the display illumination flashes red which means the signal is too high.

How is the signal too high if the peak indicator isn't lighting up occasionally?

The only time I can get the peak indicator to flash is when I turn the master volume on my mixer way up, and then I have to turn the input level on the 404 way down so that is doesn't flash red anymore (around 65), which makes the output volume of the 404 really low even when I set the output gain at 12db.

What am I doing wrong?

Could the RCA cables be the problem?

The 404sx flashes a different color on LCD screen when the start of a measure happens. It's to keep "you" in time visually.

Yes, I turn my master mixer way up till the sampler input level peaks. Usually my sampler main volume is at 25% and my scratch mixer (vestax07) is at 80%.

Correct me if I'm wrong, but I think the display only turns a different color at the start of measure when you're recording or playing patterns. When receiving sound from an external source, the SP can't determine when a measure has started or ended so it only turns red when the signal is too high.

I will correct you.

The sp404 will default at 93bpm (this is the magical number we have all come to love). The LCD will always strobe at that bpm unless you manually change the tempo. When you go to pattern mode and you hit record the strobing will sync to the time you hit record and the metronome will be in sync to the strobe.

Indeed there are different strobe modes, but again you woulda had to press the button combo and manually change the lcd screen settings. Afaik no LCD modes correlate with incoming volume. All of this is in the manual.

Once again turn main mixer volume way up till it starts to peak with the small red indicator light on the SP and then use the SP main volume knob to control how loud everything is.