Without a specific symptom described, it's hard to pinpoint the exact mistake. However, here are a few common issues that might occur in a circuit like this:
555 Timer Configuration:
The trigger, threshold, and discharge pins might be improperly connected. For example, if the timing capacitor or resistors are not correctly configured, the 555 timer might not oscillate or could produce an incorrect frequency.
Capacitor Polarity/Value Issues:
If any polar electrolytic capacitor is reversed or if the wrong capacitance is used, timing and stability can be affected.
Op-Amp Biasing and Power:
Incorrect biasing of the op-amp (OP1 1OPAMP) or lacking proper decoupling capacitors can lead to saturation or unexpected output levels.
Diode Orientation:
Diodes (D1 to D5) must be oriented correctly to provide proper rectification or protection. A reversed diode can prevent the intended current flow.
Transistor Connections:
Transistors (T1, T2, etc.) must be wired with the correct base/emitter/collector configuration. An error here could misroute signals or disrupt the switching behavior.
If you're seeing that the circuit is not oscillating, or that the timing is off, these are the areas to double-check. Could you share what specific behavior you’re observing—such as the output staying static, an incorrect frequency, or any other anomaly? This information would help narrow down the potential mistake.