A test point is a small copper pad connected to a single net and left uncovered so that a test fixture — or your probe — can touch it. Manufacturers add them for in-circuit testing and programming at the factory; repairers use them because they are the easiest, safest places to measure.
How to recognise test points
- In the schematic: a small circle or a one-pin part attached to a net, with a designator such as
TP123,T45orPAD7. - In the boardview: a round pad with no component, often drawn in a distinct shape or colour. Clicking it shows the net.
- On the board: a round gold or tinned pad, frequently on the bottom side where test fixtures press.
Not every net has one. Power rails, important control signals and programming lines usually do; many small internal signals do not.
Using test points
- Find the rail or signal you want in the schematic.
- Look for a test point on its net; note the designator.
- Locate it in the boardview and then on the board.
- Ground your meter on a solid ground point and probe the test point.
Because a test point is isolated from neighbouring pins, a slipping probe is much less likely to short anything than on a fine-pitch IC.
When there is no test point
Use the next best pad on the same net: the end of a large capacitor, an inductor pad, a resistor pad or a ferrite bead. The boardview tells you which pads belong to the net and which end of a two-pin part you are touching. Avoid probing chip pins on a powered board unless there is no alternative.
Practical tips
- Press lightly. Tinned pads are soft and easily dented; very worn boards can lose pads.
- Check the side. Many test points are on the bottom side; make sure your boardview is flipped correctly.
- Confirm the net by clicking the pad in the boardview — some test points serve different variants of the board.
- Solder a thin wire to a test point when you need to watch a signal for a long time with an oscilloscope.
More on choosing probe points in Test Points in Laptop Schematics and How to Use Them.