Our setup: four TLC5958 in series controlled by a processor. GSCLK is 33 MHz.
58 of the possible 64 RGB LEDs are mounted and our software for controlling them works.
Now for the problem:
In conjunction with updating the LEDs, some random LEDs that are supposed to be OFF actually flash for 15 us.
Not at every update, but often enough to be really disturbing.
(Updating at 1kHz gives a flash frequency of about 1-4 Hz, at random)
If we lower the GSCLK, the pulse length of the flash expands accordingly.
