77D and Travelite not in sync

[DonSRQ]

For a few years we've been using Travelite 750 strobes with a 60D and an 80D by setting on-camera flash to 1/128 power -- enough to trigger the strobes with effecting the shot. Camera set to ISO 100 and 1/100-sec shutter. However, the same setup with the 77D doesn't work -- although the on-camera flash triggers the strobe, the image captured in the camera does not catch the strobe flash. As if the shutter is operating after the strobe has finished its flash. Changing shutter sync to 2nd curtain has no effect. 

[kvbarkley]

Are you in ETTL? The strobe is probably triggering on the pre-flash

[DonSRQ]

On my 80D, Built-in flash settings shows Flash Mode is set to Manual flash.  On the 77D, however, Built-in flash settings brings up a screen which shows Built-in flash set to NormalFiring -- below which Flash mode shows E-TTL II but this setting is grey-out and cannot be selected.

[kvbarkley]

You probably need to be in one of the "Creative zone" modes, like "P". Menu menu settings are locked out in the auto modes. In the manual, these settings are noted with a '*'.

[DonSRQ]

Flash control is not available in the creative zones.

[kvbarkley]

My reading of the manual is such that you cannot set manual mode for the pop-up flash. You might need a smart flash trigger that ignores the pre-flash.