First, try checking the timing with an oscilloscope.
Literal
First [topic-は] oscilloscope [with-で] timing [object-を] check try please.
Technical troubleshooting advice. オシロ is the abbreviated form of オシロスコープ (oscilloscope). ~てみてください combines 'try doing' (~てみる) with 'please' (~てください). まずは (first of all) sets this as the first diagnostic step.