IBM PC Family - Test Equipment
In all cases below, you need to know where to measure, and you need to know what is expected to be observed at each measurement point.
( In the same way that buying medical equipment won't make you a doctor ! )
Multimeter
Very limited use. Good for measuring the voltages coming out of the power supply.
Be wary of the 'continuity' setting. It is not a short circuit indicator. For example, if I use the 'continuity' setting of my multimeter to measure a good 56 ohm resistor from my spares box, my multimeter will beep. That is because the 'continuity' setting of my multimeter beeps at anything under 100 ohms.
Logic Probe
Indicates whether a digital signal is high, or low, or pulsing. Optional memory functionality for detecting transient pulses.
An example (the model I use) is pictured at here.
Good for when timing information is unimportant. For example, I once assisted someone who had a a logic probe, to identify the faulty component in the motherboard circuitry shown at here - the keyboard interface circuitry on an IBM 5160 motherboard.
Can be used to see if the Power Good signal (a digital signal of TTL levels) out of the 51XX's power supply is high or low.
Note that because a logic probe does not convey timing information, certain use of the probe can sometimes be misleading. For example, refer to the diagram at here. Someone simply looking for lack of activity out of those chips will suspect a faulty U67 (no activity out of gate 1 of U67) whereas the faulty chip is U14.
Oscilloscope
A vintage example is pictured at here.
Typically used to view repetitive type signals.
Some examples are:
• Clocks on the motherboard, such as the one shown at here.
• Regular occurring pulses, such as the one shown at here.
• Regular occurring pulses, such as the video sync pulses shown at here.
• Radial head alignment of a floppy drive. A video showing that is at here.
• Noise levels on voltage lines (and other).
• Pulses - rise and fall times
• Pulses - overshoot and undershoot
A storage type of oscilloscope (e.g. digital storage oscilloscope) adds the ability to record one-off triggerable events. An example is at here.
Oscilloscope basics can be found in the oscilloscope documents at here.
Logic Analyser (Logic State Analyser)
An example is pictured at here.
A simple example output (capture) is pictured at here. Another is pictured at here.
You need to know which pins of which chips to monitor, you need to know what is expected on each pin in relation to the other pins, and you need to know what the trigger condition will be to set into the analyser. Basically, you need to know how the motherboard works at the low level.
In choosing a model:
- Channel count is a consideration; down the track, what is the maximum count of pins that you expect to be simultaneously monitoring ?
- Maximum sampling rate (sampling frequency) is a consideration; e.g. down the track, what timing resolution will you need ?
- Maximum sample count is a consideration.
- Will you need very flexible trigger functionality? Some models (example) have basic trigger functionality only.
Using an IC clip (example) can ease the process of hooking up the probes.