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I've knocked together a L297/L298 stepper motor controller and have a problem with what seems to be half the output. On the final 4 output lines after the L298 and diodes, I have 2 bipolar LEDs to help visualise what is going on without requiring a motor be attached at all times while debugging.

What is happening is odd and has got me stumped. One of the LEDs, the one attached to the CD / Inh2 lines works fine, however the other LED doesn't do anything. Grabbing my multimeter and measuring voltages on the Inh1/Inh2 outputs of the L297 show that the Inh1 output never changes and is always 0 whereas the other varies accordingly depending on if I'm in half or full stepping mode. I immediately thought it may be a bad chip but I've tried 3 different L297s now and all exhibit the same behaviour so it clearly isn't that.

I know this is possibly a bit vague for someone who doesn't understand a L297/L298 driver, but I'm hoping it is some easy rookie mistake that I can fix in seconds with the correct hint? Here's a schematic of the circuit I've replicated roughly:

enter image description here

from RepRap Stepper Motor Driver 1.2

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  • \$\begingroup\$ Replicated roughly? A schematic of what you actually have would help. CTRL-M to bring up the schematic editor. \$\endgroup\$
    – Phil Frost
    Jul 15, 2013 at 14:56
  • \$\begingroup\$ I'm about to go to sleep (Midnight here) but I'll do a schematic in the morning. Basically though It is exactly the same as the one above without the J1/J2 connectors and without R5, R4, C4 and C3 as these 4 are stated as optional in the Reprap documentation on this circuit. \$\endgroup\$ Jul 15, 2013 at 22:37
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    \$\begingroup\$ Well, this RepRap schematic is pretty horrible, so another schematic can only make things more clear. \$\endgroup\$
    – Phil Frost
    Jul 15, 2013 at 23:05

1 Answer 1

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pull down the control pin(11) to gnd.

Edit: From the Datasheet:

11
CONTROL
Control input that defines action of chopper. When low chopper acts on INH1 and INH2; when high chopper acts on phase lines ABCD.

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  • \$\begingroup\$ This does not explain why the OP's drive is not working as the combination of L297 and L298 WILL work in either control mode. The normal reset state for the mode the OP's circuit uses would result in both INH pins high, not one high and one stuck low (although it would be possible to step to a state where one INH pin is high and one is low). It looks like a short circuit to me. It's a shame the OP disappeared after asking this. \$\endgroup\$
    – Tut
    Nov 13, 2013 at 19:58

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