JESelectronics

One really common issue people have is making semi complex circuits on bread board and after its been working it stops suddenly.  This can be the single most devastating setbacks because often (at least when it happens to me) the problem is a bad connection inside the breadboard not a missing jumper. One of the most common reasons for this happening to me is using the wrong size jumpers.  When you bend up jumpers  they seem to get minds of their own and over time present errors like this.  Another way to have this happen a bunch is to make your own jumpers from wire that is still able to fit in the breadboard but slightly too large of AWG.  Another way is to bend the jumpers slightly to big or small which makes the wire go in at an angle and messes up the clip inside the breadboard.

There are a few ways to avoid this.  The first way is to get a large quantity of quality jumpers.  Then use the right jumpers to lay the circuit out.  As nice as the nice long jumpers are that are sold at my favorite electronics shops are (i use them too)  They are long.  On complicated circuits there will be tons of them and one will come loose.  So use the proper size jumper to go the distance you need to go .  Here is an example of this being done , on all but one jumper

Now im not trying to say this is perfect,  but I am saying that making excessively neat organized breadboards is the best way Ive found to minimize intermittent bad connections.  Breadboards are awesome but you have to be aware of their pitfalls especially those magnified by messy boards.

How to fix a board once it presents with these issues.

Start by jiggling wires that are not perfectly seated like above.  You might find things start and stop working when you jiggle the right one.

If you dont immediately find it that way get a meter and check power on each board, at the rails.  if this checks out , check at the chips vss vdd .

Check with a logic probe (about 10$) for a pulse on the clock lines if your using an external oscillator.

By this point if its not working your getting frustrated. Take a quick break, then come back and recheck EVERY THING starting with any thing you assumed was right.  Sometimes its something as small as a resistor that broke in half because it was not properly shaped to fit in the breadboard, or heavily used. Ive gone as far as to rebuild the part of the circuit  that is not working with emphasis on neatness.

Most of the test can be done really quickly to verify power , with a resistor and an led.  If the circuit has a PIC or Ucontroller  in it you can set up an i/o pin to light the led to verify the chip is starting up.  If none of these sheds light on the problem then I would try replacing difficult to test parts that might be fried, like the pic, the controller chips.

And here is an example of a messy board of mine with the exact problems im listing above , on the thick black power cable on the right. The grey tape on it is an attempt to stabilize the connection.  Laying out the circuit with proper jumpers , and then jumping the hardware with large jumpers will generally make it allot easier to locate this kind of problem.  I immediately jiggled the black power wire when it stopped working because it was the most obvious candidate and it immediately started working.

If you notice some of the red and black jumpers are too large of AWG and once I remove them this breadboard will not work reliably with proper sized jumpers.  Dont do this, it gets expensive .  Keep your jumpers straight. When you remove them use needle nose pliers to fix each one individually both the legs, and the body need to be as close to perfect as possible.  90 degree clean bend.  I go as far as to remove/insert them with needle nose to maintain the perfect shape they come with as long as possible.   Once you find a loose connection and get it working consider making a perfboard solder version. Scroll down at the link.  You will find jumper wire sets, and pcb board. Be extra aware of which board you get, some work like breadboards, some you have to solder the traces from a dot matrix.  Examine the copper and consider your layouts

@collin let me know if you are still having issues after checking this.  I suspect your problem will be solved following the steps above. If not I can look closer at it and see if i can find the problem.  I just glanced at it and didnt catch any blaring errors.

I think its your stepper leads.  I see a bit of solder on them and I would start my jiggling on them . hehe   If im right its your left board working the right is not , and its the motor leads. specifically the one between 15 and 20 on the left side of the controller chip, on the right board.