Hello.
Did same to 250 MHz. It seems the x50 options stagger the OS somehow. The x00 options seem to work. However, there is an issue. If one unlocks it above 200 MHz , the bandwidth is being reduced. At 250 MHz ( SDS1254X-E) i've found the amplitude to start to fall around 80 MHz, getting halved ( -3dB) at 120 MHz. Only have an SDG2122X, so can't test if the unlocked SDS actually can sample above this frequency. But at in 200 MHz mode (1204X-E) is flat as a table.
Another finding, the lowest limit of the horizontal system goes down to 1 ns only. Usually the 500 MHz scopes have it 500 ps ( at least that's what i saw in datasheets) or so. To be honest, i don't know the details how these digital scopes work, but according to the datasheets, there are models with 4x 250 Ms/s that can do 250 MHz, while the SDS1xxx series does 4x500 Ms/s, so there is room.
My question is, did any of you fine gentlemen experience the same issue ? If so, is there a hardware tweak, maybe some capacitor values to be changed, in the input circuitry to even out the bandwidth while unlocked above 200 MHz ? Or is it stupid to pursue this ?