Buying task · Meters, supplies and scopes
Meters, bench supplies and oscilloscopes
Which test tools a repair bench needs first: a multimeter with the right CAT rating, a current-limited bench supply, and when an oscilloscope earns its place.
We may earn a commission if you buy through links on this page, at no extra cost to you. Unless a page says otherwise, our picks come from published specifications and listing research, not hands-on testing. How we make money · How we research
Short answer
Start with a digital multimeter for voltage, resistance and continuity checks. Add a bench power supply with an adjustable current limit when you need to power boards in a controlled way, and an oscilloscope when a fault depends on signals that change over time. For anything near mains, a meter's CAT rating and an independent certification mark matter more than its display count.
What each tool does
- A digital multimeter measures voltage, current, resistance and continuity, the first checks on a faulty board.
- A bench power supply gives adjustable DC voltage with a current limit, so a faulty board can draw only what you allow. Rigol's DP700 supplies, for example, add user-set over-voltage and over-current protection that switches the output off.[1]
- An oscilloscope plots voltage against time. Tektronix defines a scope's bandwidth as the frequency at which a sine wave is attenuated to 70.7% of its amplitude (-3 dB).[2]
Multimeters: CAT rating first
A CAT rating tells you which electrical environment a meter is built to survive. Fluke's examples:
| Category | Where it applies |
|---|---|
| CAT I | Protected electronic equipment |
| CAT II | Appliances and portable tools plugged into outlets |
| CAT III | Building distribution and fixed equipment, such as switchgear and 3-phase motors |
| CAT IV | Where power enters the building: service entrances, electricity meters, outdoor lines |
A higher category means more power available and higher-energy transients.[3][4] Fluke also says test tools should be independently evaluated and certified, naming labs such as CSA, UL, TUV and Intertek (ETL).[4] The current safety standard for hand-held meters that can measure mains voltage is IEC 61010-2-033:2023.[5] Multimeter CAT ratings explained goes further.
Bench power supplies: current limit and protection
Set the current limit low before you power an unknown board, then raise it as you learn what the board draws. Beyond that, look for protection and published performance. Rigol's DP700 line, for example, lists noise under 500 µVrms, 0.01% line and load regulation and OVP/OCP; the DP711 gives 30 V at 5 A and the DP712 50 V at 3 A, both 150 W.[1] At the same power, a higher voltage range comes with less current, so match the range to your boards. Bench supplies plug into the wall, so check for a 110-120 V rating too. See how to use a bench power supply.
Oscilloscopes: when, and how much
A scope earns its place when a fault involves timing, such as clocks, ripple, start-up sequences or data lines. For bandwidth, Tektronix's "5 times rule" (at least five times the highest frequency component) keeps amplitude error under about 2%, and Keysight suggests at least 3x for analog sine waves and 5x the clock rate for digital systems.[2][6] For scale, Rigol's DHO800 line comes in 70 MHz and 100 MHz versions with 12-bit resolution.[7]
Treat budget headline figures with care: FNIRSI claims 100 MHz for its 1014D, while EEVblog users dispute some FNIRSI specifications, and we found no independent measurement either way.[8][9] Do you need an oscilloscope? helps you decide.
How to choose
- Multimeter first, rated for the highest category you will measure, with an independent certification mark if you will work anywhere near mains.
- Bench supply next, once you power boards outside their own chargers: an adjustable current limit, OVP and OCP, and a 110-120 V input.
- Oscilloscope last, when timing faults appear; size its bandwidth with the rules of thumb above.
Everything in this topic
Guides
- Do you need an oscilloscope?Helps you decide whether your repairs need a scope yet, and what bandwidth and sample rate to look for if they do.
- How to use a bench power supplyShows how to power a board from a bench supply without turning a fault into damage, and which supply features make that easier.
- Multimeter CAT ratings explainedTells you which measurement category your work needs and how to check that a meter's rating is backed by independent certification.
Common questions
Should I buy an oscilloscope or a multimeter first?
A multimeter. It answers the first questions in most repairs, such as whether power is present and whether something is shorted; a scope comes next, when you need to see a signal over time. More in Do you need an oscilloscope?
How much oscilloscope bandwidth do I need?
Use a rule with headroom: Keysight suggests at least three times the highest sine frequency for analog signals and five times the highest clock rate for digital ones, and Tektronix's five-times rule keeps amplitude error within about 2%. More in Do you need an oscilloscope?
Is 1 GSa/s enough sample rate?
It depends on the bandwidth. Keysight suggests a maximum sample rate of at least four to five times the scope's bandwidth, so on that rule 1 GSa/s suits a scope of up to about 200 to 250 MHz. More in Do you need an oscilloscope?
Are budget handheld oscilloscopes accurate?
Treat their headline figures as claims. FNIRSI lists 100 MHz for its 1014D, while EEVblog forum users dispute FNIRSI's headline specs, one estimating about 30 MHz of real bandwidth for a FNIRSI model. More in Do you need an oscilloscope?
Can I measure mains with an oscilloscope?
Not with an ordinary setup. Only use a scope on mains-powered circuits if the scope, its probes and your method are rated for it; Fluke notes that higher measurement categories carry higher-energy transients and that test tools should be independently certified. More in Do you need an oscilloscope?
What does current limiting do on a bench power supply?
It caps the current the supply will deliver. When a load tries to draw more, the supply holds the current at your limit and lets the voltage fall, which stops a shorted board from drawing everything the supply can give. More in How to use a bench power supply
What is the difference between a current limit and OCP?
A current limit keeps the output on at the set current. OCP switches the output off when current passes a threshold; Rigol's DP700 series, for example, has user-set OVP and OCP that turn the output off. More in How to use a bench power supply
Is a 30 V 5 A bench supply enough for repair?
It depends on your devices, so check the highest voltage and current they need. As a reference, Rigol's DP711 is a 30 V / 5 A model, while its DP712 trades current for voltage at 50 V / 3 A. More in How to use a bench power supply
Questions
CAT II or CAT III for electronics repair?
Choose for the highest category you will actually measure. Fluke places appliances and portable tools plugged into outlets in CAT II, and building distribution and fixed equipment such as switchgear in CAT III.[3]
Is a CAT rating printed on a cheap meter enough?
Not on its own. Fluke says test tools should be independently evaluated and certified; look for the mark of a recognized lab such as UL, CSA, TUV or Intertek's ETL, and check the lab's listing directory where it has one.[4][11]
How much oscilloscope bandwidth do I need?
Tektronix suggests at least five times the highest frequency component you need to see. Keysight suggests at least 3x for analog sine waves and 5x the clock rate for digital signals.[2][6]
What should a bench power supply have for repair work?
An adjustable current limit, over-voltage and over-current protection that switch the output off, as on Rigol's DP700 series, and published noise figures.[1]