Why is my validator not accepting all possible denominations?

There are several reasons why a validator will not accept all denominations possible. Before buying parts, review the following information and the owner’s manual of your machine.   

If the validator has been sitting and does not have a label indicting when it was last updated, it may need a software update. This is generally an option. You can verify this by inserting the older version of the bill(s). If the older bills are accepted and the new is not than the software of the validator is likely the issue.

Next, verify the dip switches are set to accept the bills desired. If the validator does not have dip switches and is configured using a coupon, then you will need to verify it is configured to accept the denominations desired.

In some cases, older machines have harnessing that was designed so only a $1 bill would be enabled. The harness can be updated or an enable board can be installed.  If the machine is an older soda machine with a single price changer, these changers can generally handle up to a $10 input provided the correct harness is installed. If you are updating a machine with a control board, verify the software on the board can handle inputs for larger denominations before buying parts. 

When using a MDB validator, it is quite possible the board in the machine is the master and has complete control of what bills are accepted. This is easy to determine by reviewing the owner’s manual of the machine.