Let's Make Robots!

Inconsistency in my L293D

Sorry, I have no schematic prepared to make this easier.

L293D by ST Electronics (datasheet) (quad half-H-bridge), only one power source: 5V from battery.
V1 = V2
Enable pins for 1+2 and for 3+4 are high.
Input pins for all half-bridges are pulled to GND via 22kOhm resistors
Motors connected to outputs: M1 to outputs 1+2, M2 to outputs 3+4.

All on the breadboard, I have an extra wire in the V+ bus. I use it to make the inputs high. Start experimenting.

experiment A)
start as above
inputs: 1 high, 2 low = M1 forwards
inputs: 1 low, 2 high = M1 backwards
leave one input (1 or 2) high, motor keeps on running, remove V+ from Enable pin "1+2", it is now floating. Motor stops

Cool = as I expected.

experiment B)
start as above
inputs: 3 high, 4 low = M2 forwards
inputs: 3 low, 4 high = M2 backwards
leave one input (3 or 4) high, motor keeps on running, remove V+ from Enable pin "3+4", it is now floating. Motor keeps on running!

What the Freak?

experiment C)
situation as produced by B)
I pull Enable "3+4" down to GND via 22kOhm resistor. Motor Stops. Finally!

experiment D)
situation as produced by A)
I pull Enable "1+2" down to GND via 22kOhm resistor. Makes no difference. Motor was already stopped.
Make enable high (with pull down resistor still in place). Motor starts running again. Makes sense.

Conclusion 1
The half bridges 1+2 need no pull down resistor on their shared enable pin. Half bridges 3+4 do. It does not hurt to pull them both down.

Experiment E)
Remove the pull down resistors on the enable pins. Make them high.
Make both motors run whichever way: for example input pins 1 and 3 high, 2 and 4 pulled low.
Remove V+ from Enable 3+4 (floating): M2 does not stop without pull down resistor on the Enable pin.
Makes sense now that we have learned the above.
Make it high again.

Experiment D)
Remove V+ from Enable pin 1+2 (floating): both motors stop!
Fudge around with some more pull down resistors on enable pins: makes no bleeping difference!

Conclusion 2
I gotta get me some sleep.

I cannot make M2 run (enable pin high) while M1 is stopped (enable pin low). But I can do that the other way around.

Suggestions? Cheap suppliers for replacement chips? Last time I spent 7 Euro.

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When I use the SN754410 (pin compat. and more powerful) I constantly drive the pin low or high, so there is no floating of the line.
I have to do the same.  I noticed all my inputs were always high on the SN754410NE and needed pull down resistors.  On my L293Ds I did not need them.