Component Signature Analyzer

I'll start this blog with a post about my current project: a component signature analyzer. 

Many of you maybe already know about it, but the signature analysis (also known as V-I testing) it's really useful when repairing electronic devices. 

The main advantage when testing a board with a V-I tester is that the device under test (usually called DUT) doesn't need to be powered up. So this technique is great for evaluating non-working boards.

What I will basically do is a resistor selector board that allows to change the current over the DUT. Then, modifying the frequency you can display a good signature on the oscilloscope display.

So basically what you'll need is a sine wave generator (from 10Hz to 50Hz), an oscilloscope with X/Y mode and a simple resistor.

  

Fig. 1: For displaying analog signatures, a variable-frequency and voltage signal source, a resistor and an oscilloscope with X/Y mode are required. The voltage drop across the device under test (DUT) drives the display in the X axis, while the measured current through the DUT drives the display's Y axis.

Picture from electronicproducts.com

So then each component will produce a different signature, depending on the current flow and the applied voltage. There are four basic Component Analog Signatures: resistance, capacitance, inductance, and semiconductance (Fig. 2). Recognizing these four basic unique signatures on the oscilloscope display is one of the keys to successful dead-boards troubleshooting.

Fig. 2:The analog signatures shown here for resistance (a), capacitance (b), inductance (c), and semiconductance (d) show typical shapes. Actual shapes may vary, but having an analog signature for a device onknown-good board lets users compare the shape of the DUT's analog signature to see if there is a deviation indicative of a fault.

Picture from electronicproducts.com

Of course there are excellent devices such as the Huntron Tracker which already integrate the function generator and the oscilloscope display in only one device, but they are really expensive (more the $7000 USD). So with a cheap function generator such as the Victor VC 2002 (127,19€) and a secod-hand Tektronix TDS210 (437,18€) I'll try to do exactly the same as the Huntron does. 

Next post will be my schematic, the PCB and some info about my Component Signature Analyzer. Meanwhile I leave here some useful links:

An analog signature analysis primer

Component Signature Analyser by Rod Elliott (ESP)

Fundamentals of Signature Analysis (Huntron)