Test points are pads the manufacturer left on the board so its factory equipment could check rails and signals without touching chip pins. For a repairer they are the safest places to probe. Knowing how to find them — and what to use when there are none — keeps your probes away from fine-pitch pins where one slip can kill a board.
What a test point is
During manufacturing, finished boards go through in-circuit test (ICT) and functional test. Fixtures with spring-loaded pins press against small round pads on the board to measure rails, check signals and sometimes program firmware. Those pads are test points. They are usually:
- small round copper pads, often gold-plated or tinned, with no part on them;
- grouped on the bottom side where the test fixture presses;
- connected to a single net each, with a designator such as
TP123,T45orPAD12.
Not every net has one. Designers add test points to power rails, key control signals, programming and debug lines, and anything the factory needs to check. Small signals inside a block often have none.
Finding test points in the schematic
In the schematic a test point is drawn as a small circle, a pad symbol or a one-pin part attached to a net. Its designator usually starts with TP or T. Some ODMs collect debug and programming test points on a dedicated page; others draw them next to the circuit they belong to.
Searching the PDF for TP produces too many hits. It is faster to start from the net: find the rail or signal you want, then look along its path for a test point symbol. If there is one, note its designator.
Finding them on the board with the boardview
The boardview is where test points become useful:
- Search the test point designator, or click any pad on the net and look for round single-pin parts that highlight.
- Note which side the test point is on. Many are on the bottom.
- Find it on the board using nearby landmarks — connectors, screw holes, large chips.
Some boardviews show test points as a distinct shape or colour, which makes them easy to spot when you highlight a net. If you are unsure how to combine both documents, see How to Use a Schematic and a Boardview Together.
What to probe when there is no test point
Most of the time you will measure on component pads instead. Good choices, from safest to riskiest:
| Point | Good for | Notes |
|---|---|---|
| Large capacitor on the rail | Rail voltages, short checks | Big pads, far from other nets |
| Inductor pads | Regulator output (output side) and switching node (input side) | Know which side is which |
| Resistor pads on a signal | Enables, power-good, resets | Pick the pull-up or series resistor |
| Ferrite bead or zero-ohm link | Branches of a rail | Also useful for isolating sections |
| Connector pins | Signals leaving the board | Fine pitch — use a sharp probe and a steady hand |
| IC pins | Last resort | High risk of bridging adjacent pins |
Two pads of the same capacitor carry two different nets — usually the rail and ground. Make sure you know which end you are touching; the boardview tells you.
Measuring safely
- Ground first. Clip the black lead to a solid ground: a screw hole pad, a USB shield, a large ground pad. A wobbly ground reference ruins readings and invites slips.
- Use sharp, insulated probes. Fine needle tips that stay where you put them. Many technicians cover most of the metal tip with heat-shrink, leaving only the point exposed.
- Approach at an angle you can control. Rest your hand on the bench or the board edge, not in mid-air.
- Never bridge pins on a powered board. Touching a high-voltage rail and a low-voltage rail at once can destroy chips instantly.
- Measure with power off first if unsure. A resistance or diode-mode reading tells you a lot and cannot damage anything.
More on this in How to Measure Voltages on a Laptop Board Safely.
Test points for diode-mode comparisons
Diode-mode readings — the red probe on ground, the black on the net, or the other way round depending on convention — are a way to compare a suspect board with a known-good one. Test points make this repeatable: the same pad on two boards gives directly comparable numbers. Some boardview files include reference diode readings for many nets; Using Diode Mode Values from Boardview Files explains how to use them and their limits.
Debug and programming test points
Some test point groups exist for engineering work rather than testing:
- EC programming pads — used to load EC firmware at the factory. They can help when an EC needs reprogramming in circuit, but the pin-out must come from the schematic.
- SPI flash pads — some boards bring the BIOS chip lines to test points as well as to the chip.
- Debug headers — unpopulated connectors for UART, JTAG or debug ports, often marked as not fitted.
Do not drive these lines without knowing the voltage level and the protocol. Many run at 1.8 V or 3.3 V, and the wrong programmer level can damage the chip behind them.
A routine for a board you have not seen before
When a new board lands on the bench, spend a few minutes building a probe map before measuring anything:
- Open the power sequence page and list the rails you will check first: system rail, always-on rails, memory rails, run rails, core rail.
- For each rail, find a test point or a large output capacitor in the boardview and note its designator and side.
- Do the same for the handful of signals that gate the sequence: the EC's enable output, the resume reset, the sleep signals and the main power-good lines. Pull-up resistors are the usual probe points here.
- Mark the ground points you will use on each side of the board.
- Keep the list next to the bench. Measuring then becomes a matter of going down the list rather than searching for each point under the microscope.
On boards you repair often, keep these maps. The second time the same model comes in, diagnosis takes half the time.
Common mistakes
- Probing through solder mask. Test points are exposed copper; ordinary traces and vias are covered. A probe on mask reads nothing or reads intermittently.
- Using the wrong side. A test point on the bottom side mirrored incorrectly in the viewer ends up on the wrong net.
- Trusting a test point label alone. On some boards a test point serves two variants of the design and is connected differently. Click it in the boardview to confirm the net.
- Scratching pads. Pressing hard on soft tinned pads leaves dents; on worn boards the pad can lift. Press only as hard as needed for a stable reading.
FAQ
Are test points the same as vias?
No. A via joins copper layers; a test point is a pad meant for probing. Some vias are left uncovered and can be probed, but most are covered by solder mask.
Why are most test points on the bottom side?
Factory test fixtures press against one side of the board, and the bottom side usually has more free space between components.
Can I solder a wire to a test point for monitoring?
Yes, with a thin wire, little heat and some care. It is a handy way to watch a rail or a signal on an oscilloscope while you work. Remove it afterwards.
My boardview shows test points the schematic does not. Why?
Some test points are added during layout and are not drawn in the schematic, or the schematic draws them on a separate page. The boardview reflects the physical board, so trust it for positions.
Bottom line
Use test points whenever the board offers them, and fall back to capacitor, inductor and resistor pads when it does not. Find them with the boardview, confirm the net, ground your meter properly and keep probes away from fine-pitch pins on a powered board.