My LM555 IC toggles the output high during power up when the output time period is for greater than 5 seconds. When it is less than 5 seconds time period the output is low during circuit power up.
Below is circuit diagram and graph during power up condition. Please do help .
There is no limiting resistor in series with variable resistor. At one end (with minimum resistance) it may cause supply to dump excessive initial current to charge the 110uF capacitors.
Your problem may not be unconnected with placement of D4 and R36. Could it be the stray capacitance of causing the effect? The combination of R36 and this stray capacitance may result in you not seeing it pull up for time less than 5sec. Investigate the trigger input, resistor, mosfet location and re-arrangement to see any improvement. Hope it helps.