While upgrading from 7.5 sp1 to 7.7.2 facing error also executed Fix75Installer.exe /q but faced below error also attached log file as reference.
2014-09-10 11:03:07 ERROR: Execution of Service Desk MSI completed. Return code: 1619, State: Failure (SetupController.ExecuteNextCommand())
I'd suggest you log this with your local support team. The installation step and error code do not match what step/code the Fix75Installer.exe tool is designed to fix.
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