The Active Probe is effectively the ‘eyes’ of the Functional Tester and can be used to detect a multitude of signals depending on what mode it is set to. To use the probe, simply connect a standard X1 Oscilloscope probe to the BNC connector located on the front panel. Once connected, the probe will be active and remain active for most times. This will be indicated by a ‘Running Dot’ on the LOWER LED display unit.
The Logic Probe is the default setting for the probe. It will detect three states as follows: LOW indicated by LO, High indicated by HI and tristate indicated by --. The LOWER LED display is dedicated to the probe and results will be shown on it at all times.
When using the logic probe, it is important not to probe voltages greater than 10V. The probe is protected but should still be used with care.
Duty Cycle & Wave Shape
When the Logic Probe is selected and a signal is probed, not only will the Level be displayed but also the Duty Cycle. This figure is shown on the first two left most digits of the lower LED display.
The Duty Cycle is a measurement of the HIGH time and LOW time and will be displayed as a percentage. For example if the signal is always LOW, then the duty cycle will be either – or 00. If it is always HIGH then the duty cycle will be 99 or --. If the duty cycle is shown as 50 then this means that for a given time, the signal spends 50% o its time LOW as well as 50% HIGH. IE a Square Wave.
If the Signal is a pulse train, Active LOW, expect a duty cycle of around 80 to 90. And if its an Active HIGH then the duty cycle will be around 10 to 20.
The middle two digits of the LED display show the type of waveform. So a 50% duty cycle will be shown as _|- . A duty cycle less than 50 will be shown as _|_ and T for greater.
By Clicking the PROBE button on the Main Test Screen, the mode of the probe is changed to an ANALOGUE type.
When this is done, the second most right LED digit displays A to indicate this. The probe will now function as an analogue type which will measure voltage levels and also trace Audio signals.
Clicking the PROBE button again will place the probe in the DIGITAL or LOGIC setting as above.
Note: By clicking the AUDIO AMP buttons, an amplifier can be switched on or off so the probe will route all signals to an amplifier as well. This can be useful for AUDIO faults.
When the probe is set to ANALOGUE indicated by an A on the LED display, the first leftmost digits will display the actual voltage measured by the probe. The range is from 0 to 100VDC and not negative or AC.
There are two ranges. The first range is from 0 to 10V and the second range 10 to 100VDC. The tester is protected against higher voltages but please exercise extreme care when checking high voltages
Another feature of the probe is that it can trace any of the processor signals used. To operate this feature, a suitable Processor Link cable is required and should be connected before running this.
Once ready, simply click the main Information Window on the MAIN TEST SCREEN and type in TRACE xx where xx is the signal required. For example, to trace the signal A6, type in TRACE A6 and hit enter. Capitals as well as lower case can be used.
The tester should display an acknowledgement and wait for approx 45 seconds.
During this time, simply place the probe on any pin on the UUT. If the pin happens to be the signal required, a short BLEEP will be given and the tester will display that its found the PIN.
If the pin is not found, the tester will timeout after about 45 seconds.
In order for the trace to work, the tester uses a Digital Signature Method relying on over 320 unique Bit patterns sent out on the pin. The probe must pick these up exactly as they are sent out for it to know its found the pin. The whole process is repeated very rapidly so briefly touching on a pin is usually enough. The method is extremely accurate and hence will not be affected by a running board and other digital signals. This means the UUT can be powered up or not as it has no affect on the results.
Bear in mind though that if the signal is buffered, then a powered down board may not return any result.