IGT Red White and Blue - reels continuously spin

[det604]

I have and IGT Red, White and Blue three reel slot machine. I get an error code 21 and all three wheels continuously spin. I know that the error 21 is a "coin in" error and I may need to get a new coin comparitor. Is it common for the reels to spin with this error or do I have another issue? Any help would be greatly appreciated.

[Buzz]

Turn the Jackpot key one time and see what happens.

[det604]

Buzz, I turned the key and the reels stop turning temporarily, but when the machine resets they start turning again.

[knagl]

I know that the error 21 is a "coin in" error and I may need to get a new coin comparitor.

Welcome to the site!   

Just so you know, on an S+, the Coin Comparator is pretty dumb and can't generate any error codes on the machine on its own.  A 21 error indicates a problem with the coin-in optics, which are located below the Coin Comparator.  You do not need to replace your coin comparator unless you have a reason to think that it, too, is faulty.

[Foster]

Usually the 21 will come up before the machine spins the reels.

Inspect the coin optics (remove the comparator)

Make sure the wiring harness that connects to the comparator, optics and  divertor solenoid is good.

Dropping a coin through the optics wont hurt and will confirm that the optic path is clear (use same coin as machine is set up to use)

Using a hobby stick (popsicle, tongue depressor) and slipping into optics also works for checking that the coin path is clear for the most part.
Some have suggested removing Q2 or Q4 depending which version of optics you have (it is a transistor) will also solve some optic board problems on the S+
 
temporarily doing a  coin optic bypass (takes 3 wires a couple inches long) machine thinks the optics are there and functioning.
I knew which pins on the coin handling connector on the door harness (15 pin molex) usually behind the coin comparator bracket.

Also are the reels spinning slow or fast.
Fast means normal reset spin (on power up, door closure)
slow means a reel tilt has occurred and needs to be reset like buzz stated.

The info is on here I just cant think of which post its in. I know Stout has posted the info, I may have as well at some time.
the optics (infrared photo-transistors) basically connect 3 inputs to ground when nothing is blocking them
the bypass does the same thing (you wont be able to play unless machine has credits but it might let you solve the reel spin issue.