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NE556 doesnt seem interchangeable with LM556 Answered

Hi, built this 556 timer-flasher many times with a NE556, always worked. Made this triple one with NE556's and can only get it to flash but not time! Put a LM556 in its place and works perfectly. Never had to do this before, but then put a 0.01uF on #3 and #11 and #4 to Vcc on a NE556 and still doesn't time. What is really weird, I built one 2 weeks ago with LM556 at ends (thought they were NE556) and a NE556 in the middle and they all worked fine, don't get it! I thought NE556 and LM556 were interchangeable.
The main components are the same, pullup resistor 10K, RGB LED, timing resistor 1M, cap 10uF, it must be something very simple I'm over looking but cant figure out what.





1 year ago

Suspect the board was bad! On a new board, the NE556 only flashes, doesn't time and most importantly doesn't get hot!
Three curious things happen though: 1. doesn't time, 2 keeping trigger constantly low, it constantly flashes but at half the rate for the given cap and R!, 3. voltage between Vcc - #7 timer (#1-556) during constant flashing oscillates between 4.6-5.9v and on the LM556 it is a constant 3.14v (same as the control voltage pin) put a 0.01uF cap on control voltage to GND and #7 oscillates between 3.8-4.1v, control voltage on the NE (which was a constant 3.14, like the LM) now oscillates between 3.0-3.3v!
The LM works perfectly! even without a cap on the control voltage or reset to Vcc.
I realize the simple solution is just use the LM556, but I have used the NE556 as a single timer-flasher many times (without a cap on the control voltage) with no problem. The first board with this sketch and a NE556 in the middle worked perfectly and still does. Replicated it with several different NEs and the NE still doesn't time. Is the NE556 really interchangeable with the LM556?