There are some symptoms/errors where it's hard to determine if a problem is the result of:

an issue with the Card Reader
an issue the reader's Wiring Harness
an issue with the Machine itself

For example, if a Card Reader is not receiving power (the reader's display is blank (with no backlight ON), or you're seeing a "Machine/Serial Communication Error" on the LaundroPortal:

These are cases where the easiest way to determine what component is causing the issue is a Swap Test.

Conducting a Swap Test

Depending on the specific issue you're troubleshooting, it is usually recommended to do a Swap test of both the Card Readers, and the reader wiring harnesses. If testing both the reader, and wiring harness, you should perform these swap tests separately.

Step 1 - Swap ONLY the Card Readers between 2 identical machines:

Do NOT change any Machine or Card Reader settings; just swap the Card Readers as they are.

Step 2 - Test out both machines to see which one now has the issue:

If the non-working machine is still NOT working, and the previously working machine IS still working; The Card Reader is not the issue.
Move both Card Readers back to their original machines, and go to Step 3
If the non-working machine STARTS working, and the previously working machine STOPS working;
you have a Card Reader issue (either it's using incorrect reader settings, and incorrect card reader board type, or there's a hardware/firmware issue with the reader itself).

Step 3 - Swap ONLY the reader Wiring Harnesses between the same 2 identical machines:

If the non-working machine is still NOT working, and the previously working machine IS still working; you're dealing with a machine specific issue.

Either the settings on the machine itself are incorrect, or there's a hardware issue with the machine. You'll want to contact your distributor for troubleshooting help with any machine specific issues.
If the non-working machine STARTS working, and the previously working machine STOPS working; you have a reader Wiring Harness issue, and the Wiring Harness needs to be repaired/replaced.

Detailed Conclusions Based on Swap Test Results

You should always start with a Card Reader swap test first, as this is usually the simpler of the 2 tests to do:

When doing a Card Reader swap test;

you should NOT change anything about the Card Readers, other than the machines they're connected to.

Leave all Card Reader settings as is (including the dip switch positions/reader numbers).

the only variable we want to change is the Card Readers being used by each machine (do NOT swap both the Card Readers and their Wiring Harnesses at the same time, as you won't be able to determine which of the 2 components were causing the issue).

When Conducting a Card Reader Swap Test:

Before considering any conclusions from the table below, you'll first want to ensure the follow is true:

The suspected bad Card Reader has been installed on a known working machine (of the same model).
The known working Card Reader has been installed on the non-working machine.
You have NOT changed any settings, on either the Card Readers or the machines involved in this swap test.

Card Reader Swap Test Results	Conclusion Based on Swap Test Result
Non-working machine still does NOT work when a known working Card Reader is installed Known working machine continues to work correctly when the suspected bad Card Reader is installed	The suspected bad Card Reader is NOT causing the issue; the card reader is working correctly. Move on to the card reader Wiring Harness swap test.
Non-working machine STARTS working correctly when a known working Card Reader is installed Known working machine STOPS working with the suspected bad Card Reader installed	The suspected bad card reader IS indeed causing the issue. First you'll want to confirm the Card Reader Settings via the LaundroPortal. The bad Card Reader should be using the exact same reader settings that the working Card Reader is using. Using the LaundroPortal, click on the Wrench Icon for both readers, and compare their settings to confirm they are identical: The most important setting to confirm is the Card Reader's Control Type setting, but if the machine's are identical, all reader settings should also be identical: If unsure about the correct reader settings to use, contact our support team If the Card Reader settings are identical, and the Card Readers are using the same Card Reader Board Type, then the bad Card Reader's Reader Board should be replaced.
Non-working machine still does NOT work when a known working Card Reader is installed Known working machine also STOPS working with the suspected bad Card Reader is installed	This is an inconclusive test. Most likely, the 2 machines involved in the swap test are NOT the same model machines, or do not have the same machine control boards installed. In these cases, the Card Readers may not be using the same Card Reader Board Type, or the Card Reader settings are not the same for these 2 machines. You'll need to find a working machine that is the same model, and using the same machine control board/reader board type, as the non-working machine
Both the Non-working AND Known working machines START working correctly after Card Readers are swapped	The suspected bad Card Reader is NOT causing the issue; the Card Reader is working correctly Most likely there was a loose wiring harness connection that was fix when the wiring harness was manipulated during the card reader swap tests. Swap the Card Readers back to their original position to confirm both machines are still working correctly.

When Conducting a Wiring Harness Swap Test:

Before considering any conclusions from the table below, you'll first want to ensure the follow is true:

The suspected bad Wiring Harness has been installed on a known working machine (of the same model).
The known working Wiring Harness has been installed on the non-working machine.
The Card Reader Swap Test concluded that the Card Reader is NOT the issue.
The Card Readers have already been returned to their original machines

Wiring Harness Swap Test Result	Conclusion Based on Swap Test Result
Non-working machine still does NOT work when using a known working Wiring Harness Known working machine continues to work correctly when using the suspected bad Wiring Harness	The suspected bad Wiring Harness is NOT the cause of the issue; the Wiring Harness is working correctly. If both the card reader, and wiring harness are working correctly, the issue must be with the machine itself. It is recommended to go through the machine's programming menus to confirm that all settings are the same between the working machine and the non-working machine. If all settings are identical, there is likely some other issue specific to the non-working machine; it is recommended you contact your distributor for troubleshooting help with the machine specific issue
Non-working machine STARTS working correctly when using a known working Wiring Harness Known working machine STOPS working when using the suspected bad Wiring Harness	The suspected bad reader Wiring Harness IS indeed causing the issue. The card reader's Wiring Harness should be replaced/repaired. If the reader Wiring Harness has any spliced connections, double check all spliced connections; it's possible one of the spliced connections may be loose/is connected to the wrong wire(s). If all spliced connections are good, and the Wiring Harnesses are connected to both machines in the same manner; then the suspected bad Wiring Harness should be replaced.
Non-working machine still does NOT work when using a known working Wiring Harness Known working machine also STOPS working when using the suspected bad Wiring Harness	This is an inconclusive test. Confirm that both Wiring Harnesses are the exact same; that they are connected to both machines in the same manner; and that the are connected to the correct spots on the machines. Double check the connections from a working machine, or consult our reader installation guide for your specific machine, if you are unsure the Wiring Harnesses are connected correctly. If there are any spliced connections, double check to ensure all splices are making a good/solid connection with the wires being spliced. In these scenarios, it's most likely that the 2 wiring harnesses are not exactly the same, or have not been connected to the machines how they were originally connected when the known working machine was working correctly
Both the Non-working AND Known working machines START working correctly after the reader Wiring Harnesses have been swapped	The suspected bad reader Wiring Harness IS working correctly. Most likely there was a lose Wiring Harness connection, that was resolved when the Wiring Harnesses were swapped during this test. No need to swap harnesses back to their original positions, since they are identical and both machines are now working.

Things to look out for when conducting swap tests

When conducting a Card Reader or Wiring Harness swap test,

at any point, if you are unsure about the results of your swap test(s), get in touch with our support team, let us know the results of your tests and we will help you narrow down which component is the most likely cause of the issue.

When doing a Card Reader swap test

During the swap you should always verify that you are swapping Card Readers that are using the exact same Reader Board Type!

When selecting machines of the same model type, the readers installed on those machines should also be of the same reader board type,

however if you're doing a swap test, you can easily confirm the reader board types by checking the stickers on the back of the card reader boards themselves.

Below are pictures of 3 different card reader board types as examples

(a Compass Serial, a Generic Serial, and a Generic Relay Card Reader board type):

All readers boards will have a sticker on the back that says what type of reader board is it.

The numbers on these stickers are not relevant when looking for the reader board type; just compare the name's of the boards and make sure they are identical.

You can also review the Card Reader installation guide for your particular machine to confirm which reader board type is used with your machine's specific control board.

When doing a reader Wiring Harness Swap Test

During the swap you can easily verify that you are swapping identical wiring harnesses by checking the wiring harness part number listed on the wiring harness itself.
Below are a few examples so you can see where you'll find the wiring harness part number:

You can also review the Card Reader installation guide for your particular machine to confirm which Card Reader wiring harness is used with your machine's specific control board.

Reader Swap Test: Isolating Reader, Machine, or Cable Harness Faults