What's to blame when your cables fail?

failed testWhat’s worse than a failed cable? All your cables failing and you don’t know why. Failed tests can be one of the most frustrating misfortunes a cable manufacturer can endure. After weeks and months of wiring and pinning, the cables fail during the final test. The cause is unknown because of the many potential causes for the failure. Maybe the cable is bad, or the fixturing is defective, or there is a problem with the tester. What is causing the errors and how can they be resolved?

Possible causes

The source of the problem will most likely be found in one of three places. The failure is caused by the cable, fixturing, or tester. You can use process of elimination to determine which location is the culprit.


Test programs are created on Cirris testers by attaching a cable to the tester and using the “Learn” feature. The tester uses the cable to create instructions for a test program.

If a bad cable (meaning a cable with mistakes or defects) is used as the primary cable to create the test program, then all good cables will fail because they are tested using bad test instructions.

The easiest way to discover if this is the problem is by creating a new test program using a different cable. Connect another cable to the tester and use the “Learn” feature to create new test instructions. If cables still fail tests using the new test program, there is a good chance the cable is not the cause of the failures.

If you have another tester, test the cables on the alternative tester. If they pass on another system, the problem is more likely caused by the fixturing or tester interface.


Fixturing refers to the cables that connect the tester and the device-under-test. The device-under-test, or DUT, is another name for the cable in need of testing. The DUT does not always have connectors that can attach direcly to the tester. Fixturing creates a way to attach the DUT to the tester. If the fixturing is not built and installed correctly it can result in failed tests.

To eliminate fixturing as a cause of the failure, perform a “Learn” and test the fixturing without the DUT attached. If the error still occurs, you will know the problem is not the DUT but could possibly be in the fixturing. Proceed to test the tester interface to see if the error continues to occur.

If you determine the error is caused by the fixturing, you can replace or repair the fixturing.

Tester interface

If the DUT and fixturing have both been ruled out as sources for the failure, something about the tester interface or unit may be causing cables to fail. While this doesn’t happen often, occasionally defects occur in testers to the point of failing good cables.

A problem with the tester may occur on the tester interface, meaning the part of the tester visible to the user, or within the tester unit, meaning the wiring and other pieces contained inside the chassis. Problems with the tester interface could be repaired by the user while problems with the tester unit may have to be looked at by the tester manufacturer.

If your shop has more than one tester, you can analyze the cables and fixturing on a different tester to determine if the tester is bad. If you conclude the tester is the cause of the errors, inspect your tester for obvious signs of defects. Replace adapters and verify no debris (especially metal debris) is located in the test area.

Should the problem persist, call the tester’s manufacturer for further instruction about repairs or replacements.

Type of Errors

While narrowing down the cause of failed cables, pay attention to the type of error occurring. For example, if the error appears as a high voltage (hipot) error, such as a dielectric failure, you could have an easier time finding the source of the issue.

To troubleshoot a high voltage failure such as a dielectric failure, remove the DUT and Learn a new test program with the same high voltage settings. The tester may send an alert indicating no cables are attached. Proceed to perform the Learn and test. If the same dielectric failure occurs, you will know the problem is either with the test fixture or the tester interface. Detach the fixturing and perform the Learn and test again. If the dielectric failure does not appear, you know the problem is located in the fixturing. If the error appears, the tester is the source of the problem.

Before panicking over unknown failures, try to find the source of the problem. Once you’ve identified what to blame, you can begin repairing the issue. This may involve rebuilding equipment or contacting the manufacturer.

If you have questions about any Cirris equipment you’ve purchased,