Double diamond coin throwing error 21

[acstiefel323@gmail.com]

I have a double diamond igt from 1993. It has a bill validator, but I can’t get it to work. The quarter works for a bit and then it throws the 21 code. I saw that it could mean battery, but I thought that was 12. Anyways, I’ll take all the help I can get. Thank you all in advance! I attached a picture, ignore that code, I was able to find the answer for that on here. Thanks again!

[Stayouttadabunker]

Go to the NLG Homepage, scroll down to Rick's FAQs on the right-hand side of the page.
Lotsa answers for you there! 
Here's a direct link for your validator qquestion...>>>

/spset/dbv.htm

[acstiefel323@gmail.com]

Thank you!
I read all of Rick’s FAQs. I just want to make sure I understood correctly. If opening the door/closing door doesn’t clear my 21 error, I should get the clear chip and do the swap, etc. I should also get the SET chip because I’ll need it for the bill validator.

I was trying to just bypass the error 21 by using the bill validator, but it won’t take money. It is set to 9 1, the validator makes noise when the machine first starts and has tiny red lights inside it that I can see the whole time, but the yellow part isn’t lit up outside and it won’t even try to take the bills.

[Stayouttadabunker]

Check and see if there's anything blocking the ABC optics board located directly underneath the coin comparitor.
Inside of the sandwiched boards are a coin guide with three small holes for the infrared light beams to go through.
Sometimes dust gets in there and blocks the beams...shooting out a [21] code.
You can just blow it out to help clear the holes.

Another way of getting a [21] code is a coin blocking the coin hopper optics that counts the coins as they exit the hopper bowl.

Your yellow bill bezel won't light up if there's something else wrong with the machine.
It needs to be lit up (providing the lamps are good of course) or the acceptor will not pull in a bill.

[acstiefel323@gmail.com]

The machine will play fine for 10-15 minutes before it starts saying error 21. The bill validator never lights up.
I will check the ABC optics. I did check the hopper optics last night. Thank you!