After applying the sequence provided in quantalume's post yesterday to my FY3206S 6 MHz generator I see that
ALL the wave shapes can now be turned up to 24 MHz. The official manual/specs list 6 MHz max for square, triangle, arbitrary no matter which version. So, this hack has unlocked the frequency setting for everything up to 24 MHz
Of course, the generator does not have enough bandwidth to do a good job for square or triangle at 24 MHz. However it is definitely usable beyond 6 MHz. I tried a square at 6.6 Vp-p (with 50 Ohm termination 3.3V p-p for a logic signal) and found usable results beyond 6 MHz.
Square:
Set 6.6 Vp-p and scope has 50 Ohm termination
0.1 MHz 3.26 Vpp (Reference) great square shape
1.0 MHz 3.24 Vpp (- 0.6%) good square shape 26 nSec rise time
6.0 MHz 3.22 Vpp (-1.2%) OK square shape 24 nSec rise time flat top for 90 degrees (ideal would be 180)
10.0 MHz 3.14 Vpp (-3.7%) Usable square shape 24 nSec rise time barely any flat top
15.0 MHz 2.68 Vpp (-18%) Barely usable, basically a sine wave shape
24.0 MHz 1.68 Vpp (-49%) Unusable, basically a sine wave
See below oscilloscope shot of 10 MHz square. This scope shot shows the trigger wave and CH1 out. The phase lag from trigger to CH1 out is 14 nSec or 50 Deg and probably all of this is from the output low pass filter. As quantalume commented the trigger signal is quite fast with about 2 nSec rise time (at least on my 200 MHz analog BW scope).
I also tried 10 MHz square with duty at 33% and the amplitude was 2.91 Vpp which is still quite usable.
I quickly checked the sine shape at 24 MHz and found the amplitude to be down by 1.58/3.24 = -6.2 dB and it lags the trigger by 25.6 nSec/220 Degrees. This data matches the results when putting 4 sine cycles in an Arb waveform and running at 6 Mhz rep rate for 24 MHz out that I reported earlier. This confirms to me that this FY3206S generator output filter is causing the limit.