Thanks for quick reply, Ron. First time, we did not have pull up on the first 555 and no diode installed. First 555 and third 555 got damaged - their VCC to GND read about 15 Ohms. Second time, with pull up and no diode, second 555 (middle one) got damaged with its VCC to GND read about 15 Ohms. Third time, just the first 555 CIRCUIT alone (first stage), output varied ~ 200 - 240 ms every time push switch toggles. The RA and CA values were 15k and 1 uF - expect for 16.5 ms. Thanks.
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