Put simply, the Go / NoGo method involves testing a module or unit (sometimes referred to as a Unit Under Test – UUT) to see if it is working (Go) or not working (No Go).

All Diagnosys systems perform functional testing on modules or UUTs.

Sometimes this type of testing can be challenging. The test code is written and sequenced to prove the unit works to a pre-determined set of conditions. Producing the test program for a unit requires an understanding of its function, or a test specification and sequence, such that the test code can be produced and written manually. There is no alternative and this process will take a finite time.

When a unit fails this testing process, the task turns to diagnosing the cause of the failure so that remedial work can be performed.

This technique applies and measures signals to a module or circuit. The input signals are created by the programmer and the output can be manually predicted, learnt from a known good circuit or may be taken from a logic simulator. This is the fastest way to test a circuit but has the longest program development time. The technique is often used to prove the performance of the circuit and as a final confidence check on the circuit.

Types of fault detected:

  • Fan-out
  • Timing – fast / slow edges, propagation
  • Faulty devices
  • Short circuits, open circuits

Functional test cannot detect:

  • Pull-up or Pull-down resistor missing
  • Capacitors missing (eg decoupling)
  • Passive component values
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Diagnosys' products with Functional Testing Capability


The Diagnosys S790 Series2 with its high technical specification hardware and technology, represents the ultimate high-performance, precision test ATE system.


The S500 is an easy-to-use turnkey functional test solution for your LRUs, PCBs and electronic assemblies

PinPoint II R

The PinPoint II R provides industry leading capability for the test and fault finding of the most challenging circuits. Allowing you to select and apply different test techniques on a single circuit, comprehensive fault coverage is ensured.