EEVblog BM786 user guide: every feature, and how and when to use it.

The EEVblog BM786 has nine dial positions, eight buttons and five settings you reach by holding a button while you switch it on. Most of them do two or three jobs. This guide goes through every one: what it measures, which socket the red lead goes in, the steps, and where it earns its keep on a real bench. It's built from Brymen's manual and datasheet (Brymen makes the meter for EEVblog), with the layout checked against our own BM786. If you haven't got one yet, start with why we bought ours.

Before you open Brymen's manual: its drawings show the BM789, a sister model with extra functions. The BM786 has no Auto-V/LoZ dial position, no dBm, one thermocouple input instead of two, and AC accuracy specified to 7 kHz rather than 100 kHz. Everything on this page is for the BM786.

Safety first

A good meter only protects you if it's used the right way. Brymen's manual, boiled down:

• Treat anything above 30 V AC (42.4 V peak) or 60 V DC as able to give you a shock. Those are the manual's thresholds for taking proper precautions.
• Keep your fingers behind the finger guards on the probes, and check the leads for cracked insulation or bare metal before you start. Replace damaged leads; don't tape them.
• Take the probes off the circuit before you turn the dial.
• Prove the meter works first. Before and after measuring a dangerous voltage, check the meter on a known live source, so a zero reading means a dead circuit and not a dead meter.
• Never measure voltage with the red lead in a current socket (µA mA or A). The meter warns you if you try: see BeepJack.
• Resistance, continuity, diode and capacitance are for circuits with the power off. On a live circuit they give false readings and can damage the meter. Discharge capacitors first.
• Indoors and dry only. The meter isn't made for rain or moisture.
• The lowest rating in the chain applies. The meter is rated CAT III 1000 V and CAT IV 600 V (what that means), but probe caps and clip-on accessories carry their own ratings. Brymen notes that for CAT III and CAT IV work the standard allows no more than 4 mm of bare probe tip.
• In Australia, fixed wiring is for licensed electricians. A meter's rating doesn't change that. We use ours on batteries, electronics and low-voltage gear, and leave the switchboard and mains wiring to electricians.

The layout at a glance

From top to bottom: the display, two rows of four buttons, the rotary dial and four sockets. The dial picks the kind of measurement. The yellow SELECT button picks between the two to five functions that share each dial position. The other seven buttons add features on top, like holding, recording or catching peaks.

Each dial position remembers its last function, even after you switch off. If you used VFD volts or AC+DC volts last time, that's what you'll get next time. Before you trust a reading, glance at the symbols on the left of the display, and press SELECT if they're not what you want.

Brymen's datasheet also lists probe holders and a tilt stand on the over-moulded holster, and an optional BMH-02 magnetic hanger strap for hanging the meter off a metal surface.

Which socket the leads go in

The black lead lives in COM. The red lead moves, and putting it in the wrong socket is the commonest way to blow a fuse.

The BeepJack warning

The small speaker symbols above the µA mA and A sockets mean the meter is watching them. If a plug is in either one while the dial is on anything other than a current function (most dangerously, volts), the meter beeps and shows InEr, for input error. Stop, and move the red lead back to V Ω before the probes touch anything.

It's there because of a classic mistake: you measure current, forget the red lead is still in A, then put the probes across a battery or a power supply to read its voltage. The current socket is close to a short circuit, so the fuse blows, or worse. BeepJack catches it before you touch anything.

Reading the display

Counts, ranges and the smallest step

The display shows up to 60,000 counts: on the volts, current and resistance ranges the biggest number it can show is 59,999, so the 6 V range, for example, shows up to 5.9999 V. The digits update about five times a second. Here's every range and the finest step the meter can show:

How to read an accuracy figure

Brymen gives accuracy as ± (a percentage of the reading + a number of digits). The digits are counts of the last place on the display. Take a car battery reading 12.600 V on the 60 V range, where DC accuracy is ±(0.03% + 2 digits):

• 0.03% of 12.600 V is 0.0038 V;
• 2 digits on the 60.000 V range is 2 × 0.001 V = 0.002 V;
• so the true voltage is within about ±0.006 V: somewhere between 12.594 and 12.606 V.

Those figures hold for a year after calibration, at 18 to 28 °C and below 75% humidity. Outside that temperature band, Brymen adds a tenth of the stated accuracy for every degree (a fifth on ohms and capacitance).

The bar graph

Under the digits is a 31-segment bar graph that updates 50 times a second, ten times as fast as the digits. Brymen likens it to an old analogue needle, and that's how to use it: watch it for things too quick for the numbers. It shows a flickering bad contact, the scratchy spots on a worn potentiometer, a brief spike, or which way a reading is heading while you adjust something. When you're tuning a trimmer to a peak or a dip, watch the bar, then read the digits.

Symbols and messages

Which setting for which job

A quick reference before the detail. The dial numbers match the map.

The dial, position by position

For each position: what SELECT steps through, the ranges and accuracy, how to use it, and where it's useful. The accuracy figures are Brymen's for the BM786.

2 · V~: AC volts, and VFD volts

SELECT: AC volts → VFD AC volts · red lead: V Ω

AC volts measures alternating voltage as true RMS: the value that does the same work as that much DC, even when the waveform isn't a clean sine wave. That matters on the output of cheap inverters, light dimmers and anything with a switch-mode power supply, where an average-reading meter can be well out.

The input impedance is 10 MΩ. Two quirks are normal and in the spec:

• With the probes shorted together, AC can show up to 50 digits rather than zero. That's normal for a true RMS meter at the bottom of a range.
• Crest factor limit. Crest factor is a waveform's peak divided by its RMS: 1.41 for a sine wave, much higher for spiky ones. The BM786 handles up to 1.6 near full scale and 3.2 at half scale. For a spiky waveform near the top of a range, press RANGE twice (once to lock the range, once to step up) to get the extra headroom.

Ghost voltages. A 10 MΩ input barely loads the circuit, so a disconnected wire that runs beside a live one can pick up enough voltage by capacitance to show a reading that isn't really there. The BM789 has a low-impedance (LoZ) mode to drain these; the BM786 doesn't. Ghost readings can be anything up to close to mains voltage, and this meter can't tell them from the real thing. On mains wiring, treat any reading as live, and call an electrician.

VFD volts (press SELECT; VFD shows on the display) turns on a low-pass filter for the output of variable-frequency drives, the motor controllers that run variable-speed pumps, fans and machine tools. Their output is a chopped, high-frequency waveform that throws off an ordinary reading; the filter lets the meter read the part that actually drives the motor. It works on the 600 V and 1000 V ranges only: ±(4% + 50 digits) from 10 to 200 Hz, worsening to ±(10% + 50 digits) at 440 Hz, and unspecified above that. Turn it on and press ~Hz to read the drive's output frequency too.

Motor drives are electricians' and technicians' territory. If you don't work on them, keep VFD off: on an ordinary supply it reads about the same, with looser accuracy.

How:

1. Black lead in COM, red lead in V Ω.
2. Dial to V~. Check the display shows ~ and not VFD; press SELECT if it does.
3. Put the probes across the two points. Polarity doesn't matter on AC.
4. Press ~Hz if you also want the frequency.

Where we'd use it: AC plug packs (some alarm panels, CCTV cameras, doorbells and garden lights run on 12 to 24 V AC), the low-voltage side of a transformer, and audio signals at a test tone of about 1 kHz. For quiet signals below 600 mV, use the mV position. Mains voltage is within the meter's ratings, but it's the measurement most likely to hurt you, and we leave mains testing to electricians.

3 · V: DC volts, and AC+DC volts

SELECT: DC volts → AC+DC volts · red lead: V Ω

DC volts is the setting you'll use most, and where the BM786 is at its best:

Polarity is automatic. A minus sign just means the red probe is on the more negative point. The 10 MΩ input is light enough for almost everything, but on very high-resistance circuits, such as a divider made of megohm resistors, the meter itself pulls the voltage down and reads low.

AC+DC volts is the true RMS of the whole signal, DC included. Think of it this way: DC volts shows the average, AC volts shows only the wobble, and AC+DC shows the total effective value, the one that sets how hot a resistor or a heating element gets. Use it for a supply with heavy ripple, the raw output of a rectifier, or a PWM-dimmed LED strip. Accuracy is ±(0.7% + 40 digits) at 50 to 60 Hz, ±(1.4% + 40 digits) for DC and 40 Hz to 1 kHz, and ±(2.2% + 50 digits) from 1 to 7 kHz, adding 1% above 5 kHz; the 1000 V range isn't specified above 1 kHz.

How:

1. Black lead in COM, red lead in V Ω.
2. Dial to V. Check the display shows the DC symbol (a straight line over dashes) and press SELECT if it shows AC+DC.
3. Red probe on the positive point, black on the negative or ground.

Where we'd use it: batteries of every kind (our battery guide has the method and the charts), laptop and router power bricks (the barrel plugs are in our connector reference), PC power supply rails, car electrics, and small 12 V solar panels (rooftop arrays run at hundreds of volts DC and are work for accredited installers). The 0.1 mV steps on the 6 V range and 1 mV steps on the 60 V range are what make the meter good for batteries, where a small difference in voltage can mean a big difference in charge.

4 · mV: millivolts, logic frequency and duty cycle

SELECT: DC mV → AC mV → AC+DC mV → logic Hz → duty % · red lead: V Ω

DC mV is a single 600.00 mV range with 0.01 mV (10 µV) steps, at the same ±(0.03% + 2 digits) as DC volts. Small voltages tell you a lot:

• Voltage drop. With the circuit working, measure across a switch, a plug, a crimp or a length of cable. A good connection drops very little, so compare against a known-good one. A noticeably bigger drop across a battery lead, a crimp or a fuse holder under load means resistance where there shouldn't be any, and that's where heat and faults come from.
• Current through a shunt. Many circuits have a low-value resistor in series for current sensing. Measure the millivolts across it and divide by its resistance: 25 mV across a 0.01 Ω shunt is 2.5 A, and you haven't had to break the circuit.

AC mV is the 600 mV range in true RMS: ±(0.5% + 30 digits) at 50 to 60 Hz, ±(1.2% + 30 digits) from 40 Hz to 1 kHz and ±(2.0% + 40 digits) from 1 to 7 kHz. AC+DC mV is ±(0.7% + 40 digits) at 50 to 60 Hz, ±(1.4% + 40 digits) at DC and from 40 Hz to 1 kHz, and ±(2.2% + 50 digits) from 1 to 7 kHz. Both add 1% above 5 kHz, and the signal's peaks, DC included, must stay under 1000 mV. Use them for line-level audio (a few hundred millivolts) with a 1 kHz test tone, or the AC ripple riding on a small DC signal.

Logic Hz (the square-wave symbol) counts the frequency of digital signals from 5 Hz to 1 MHz at ±(0.002% + 4 digits). It needs a square wave of more than 3.0 V peak with pulses longer than 0.5 µs, so 5 V logic works, and 3.3 V logic only just clears it. Duty % shows how much of each cycle the signal spends high:

Accuracy is ±(3 digits per kHz + 2 digits). How: black probe on the circuit's ground, red on the signal, dial to mV, then press SELECT until the square-wave symbol and Hz show, and once more for %. Where: a microcontroller's PWM pin, a 555 timer, an oscillator, or the control wire of a 4-pin PC fan, to check a signal is there and at the speed you expect. For sine waves and mains-type signals, use the ~Hz button on a volts position instead.

5 · Ω: resistance, continuity and nS

SELECT: resistance → continuity → nS (conductance) · red lead: V Ω · power off

Resistance autoranges across six ranges:

The meter tests with less than 1.3 V (1.5 V on the 600 Ω range). How:

1. Power off, and disconnect at least one end of the part if you can: anything else connected across it gives the current another path and the reading comes out low.
2. Black lead in COM, red in V Ω, dial to Ω.
3. For small values, zero the leads: touch the probe tips together, press Δ, then measure. The meter subtracts the leads' own resistance.
4. Don't hold both probe tips with your fingers on high values. Your body is then in parallel with the part, and you'll read yourself.

Where: resistors, potentiometers (watch the bar graph for scratchy spots as you turn it), heating elements, speaker coils, thermistors, and the pull-up resistors in a project.

Continuity (the sound-wave symbol) is Brymen's BeepLit tester: a beep and a flash of the backlight when the probes connect, so you can follow it on a noisy bench or with your eyes on the probes. It responds in under 100 µs. Two things depend on the firmware:

• Threshold. Brymen's documents give three figures: 100 to 420 Ω in the manual's specifications, 20 to 200 Ω on the datasheet, and 40 Ω from firmware version 12 in the manual's change log (down from 270 Ω). On version 12 a 100 Ω resistor shouldn't beep; check your version.
• Non-latched. Version 11 changed the beeper from latched (each contact, however brief, stretched into a beep of a set length) to non-latched, so the sound follows the contact. An intermittent break crackles instead of beeping cleanly, which is exactly what you want when hunting one.

Continuity still beeps even when you've turned the beeper off. Where: checking a cable end to end (pinouts are in our connector reference), finding which wire is which in a multi-core cable, fuses out of their holders, switches, and PCB tracks. To find an intermittent break, keep the probes on both ends and flex the cable along its length, listening for the crackle.

nS (nanosiemens) measures conductance, the inverse of resistance, so it can go where the ohms ranges run out. Its single 99.99 nS range starts at 10 MΩ (99.99 nS) and runs up into the gigaohms: 1 nS is 1 GΩ. To convert, divide 1000 by the nS reading to get megohms: 2.00 nS is 500 MΩ, 0.50 nS is 2,000 MΩ. Accuracy is ±(1.0% + 10 digits), with 30 more digits below 10 nS, and the test current is a tiny 0.01 µA. That's about ±0.4 nS on readings under 1 nS, so treat gigaohm figures as rough.

Where: leakage. Between two tracks on a circuit board after liquid damage or heavy flux, across a cable's insulation, through a dirty connector, or in a very high-value resistor. Keep your fingers off both probes; your skin conducts far more than a nanosiemens. One honest limit: this tests at about a volt. It isn't an insulation-resistance test of the kind electricians do at 500 or 1000 V, and it won't find faults that only break down at high voltage.

6 · Capacitance and diode test

SELECT: capacitance → diode · red lead: V Ω · power off

Capacitance runs from 10.00 nF up to 10.00 mF (10,000 µF) and is autorange only; RANGE does nothing here.

Those figures are for film capacitors or better. How:

1. Discharge the capacitor first. Large ones through a suitable resistor, not a screwdriver. A charged capacitor can damage the meter and, in mains gear, hurt you.
2. Take it out of the circuit, or at least lift one leg.
3. Black in COM, red in V Ω, dial to the capacitor symbol. On an electrolytic, red probe to + and black to −.
4. Wait for the reading to settle. Big capacitors take longer.

Where: motor-run capacitors in fans, pumps and air-conditioners (often mains-connected, so they're an electrician's job in place), timing and filter capacitors, and checking a part matches its marking. The limit: capacitance alone doesn't prove a capacitor is good. A dried-out electrolytic can read close to its value and still fail because of high internal resistance (ESR), which this meter doesn't measure.

Diode test pushes about 0.35 mA through the part and shows the voltage across it on a 3.0000 V range, with up to 3.1 V available. With the red probe on the anode and black on the cathode (the end with the stripe):

• 0.400 to 0.900 V: a good silicon diode, forward biased.
• Higher: leaky (Brymen calls it defective). Zero: shorted. OL: open.
• Reverse the probes: a good diode shows OL. Anything else means it's resistive or shorted.
• Schottky and germanium diodes read lower, roughly 0.15 to 0.45 V, and that's normal for them.

Accuracy is ±(1% + 20 digits). It's also BeepLit: a short beep as the reading falls past 0.850 V, so you can test a row of diodes without looking, and a continuous beep plus backlight flash below 0.100 V, which means a short or a straight wire. That makes diode mode a continuity tester with a voltage threshold rather than a resistance one.

LEDs: red, orange and yellow LEDs usually show their forward voltage and may glow faintly. Blue, white and bright "true green" ones need close to 3 V and can read OL with only 3.1 V available, so OL on one of those doesn't prove it's dead. Transistors: the base-emitter and base-collector junctions each test like a diode.

7 · Temperature

SELECT: °C ↔ °F (if both are enabled) · thermocouple: + pin in V Ω, − pin in COM

The meter reads a type K thermocouple from −200.0 °C to 1090 °C at ±(1.0% + 1.0 °C), or −328.0 °F to 1994 °F at ±(1.0% + 1.8 °F). That accuracy is the meter's alone: the probe adds its own error, and its own temperature limit. The BM786 comes with Brymen's Bkp60 bead probe on a banana plug; Brymen's optional Bkb32 adapter takes standard miniature type K plugs.

How:

1. Plug the thermocouple in, + pin to V Ω and − pin to COM. Reversed, it reads wrong.
2. Dial to the thermometer. Press SELECT to swap °C and °F if both are enabled (see power-on options).
3. Hold the bead firmly against the surface, or in the air or liquid you're measuring, and wait for the reading to stop moving.

Let the meter settle. A thermocouple measures the difference between its tip and the point where it plugs in, and the meter compensates for the plug end with its own internal temperature. That only works when the meter, plug and sockets are all at room temperature. After you bring the meter in from a hot car or a cold room, Brymen says it can take up to an hour to settle for a change of more than 5 °C. Don't hold the plug in your hand while measuring, and if you use the Bkb32 adapter, give it time to settle too.

Where: a heatsink or a laptop charger that seems too hot, a 3D printer bed, a fridge or freezer, the air in a comms cupboard. Pair it with REC to get the overnight high and low.

8 · A mA: amps and milliamps

SELECT: DC → AC → AC+DC · red lead: µA mA (milliamps) or A (amps) · in series

This position reads milliamps or amps, and the socket decides which: with the red lead in µA mA you get the 60.000 mA and 600.00 mA ranges; in A, the 6.0000 A and 10.000 A ranges. Your DC, AC or AC+DC choice is shared by all the current functions.

Current is measured in series. Voltage is measured across a part with the circuit untouched. Current has to flow through the meter, so you break the circuit and put the meter in the gap:

How:

1. Switch the circuit off.
2. Black lead in COM. Red lead in µA mA if you're sure the current is under 600 mA; otherwise, or if you don't know, start in A.
3. Dial to A mA. Check DC or AC on the display.
4. Open the circuit at one point and connect the meter across the gap: red to the side nearer the supply's positive, black to the side going on to the load.
5. Switch on and read. Switch off before you disconnect.
6. Put the red lead straight back in V Ω. BeepJack will nag you if you don't.

Time limits on the A socket. 10 A is continuous up to 40 °C room temperature. From 40 to 55 °C, keep it to 3 minutes on and at least 15 minutes off. Between 10 and 20 A, no more than 30 seconds on, then at least 15 minutes off.

Burden voltage is the voltage the meter itself drops while current flows through it. At 600 mA on the µA mA socket that's 1.2 V, a big slice of a 3.3 V or 5 V circuit, enough to make it brown out or reset. If a circuit misbehaves with the meter in it, move the red lead to A (0.3 V even at 10 A), or measure the millivolts across a known shunt instead (see mV).

Brymen notes that a few negative counts with the input shorted are normal on the most sensitive current ranges; they don't affect real readings.

Where: how much a gadget, an LED strip or a project draws; whether a charger is really charging; a car's battery drain with everything off (start in A: a car's modules can draw a lot for a while after you lock it, and never start the engine or turn on the headlights with the meter in series). Not for mains appliances: putting the meter in series with mains is a job for a clamp meter or a plug-in power meter, not test leads.

9 · µA: microamps

SELECT: DC → AC → AC+DC · red lead: µA mA · in series

Two ranges, 600.00 µA and 6000.0 µA, through the µA mA socket, at ±(0.075% + 20 digits) DC, ±(0.9% + 20 digits) AC and ±(1.0% + 30 digits) AC+DC. The burden is 0.2 mV per µA: 120 mV at 600 µA, but 1.2 V at 6000 µA. Connect it in series exactly as for milliamps.

Where: the standby or sleep current of battery gear, which is what decides how long the batteries last. Remote controls, wireless sensors, smoke alarms, a microcontroller in deep sleep, or a device that flattens its battery while switched off. If the reading shows OL when the device wakes up, it's drawing more than 6000 µA: switch the circuit off, turn the dial to A mA (same socket) and measure again.

The buttons

Most buttons do one thing on a short press and another if you hold them for a second or more. Five also change a setting if you hold them while you turn the dial from OFF.

Cheat sheet

SELECT: the next function, and the backlight

A short press steps through the functions that share the dial position you're on: AC and VFD volts, DC and AC+DC volts, the five mV functions, and so on. The meter remembers your choice for each position, even after you switch off. Hold SELECT for a second to turn the backlight on or off; it switches itself off after about 16 minutes without use. A short press of SELECT also wakes the meter after auto power-off.

RANGE: choosing the range yourself

The meter autoranges by default (AUTO on the display). A short press of RANGE locks it on the range it's in, and AUTO goes off; each further press steps to the next range. Hold RANGE for a second to go back to autoranging. Manual ranging isn't available on capacitance or the frequency functions.

When to lock the range:

• A reading that keeps jumping between two ranges, like a voltage hovering around 6 V.
• Before REC. Brymen specifies recording accuracy with the range locked, and a range change in the middle of a recording is the last thing you want.
• A string of similar readings, like a tray of batteries: the meter doesn't stop to pick a range every time you touch the probes.
• Headroom for a spiky AC waveform near the top of a range (see crest factor).

If a locked range shows OL, the value is too big for it: press RANGE to step up.

Δ: relative (zero) mode

Press Δ and the meter stores the current reading and from then on shows the difference from it; Δ shows on the display. Press it again to go back to normal readings.

• Zero the leads before a low resistance reading: probes together, press Δ, then measure.
• Compare against a reference: measure a known-good resistor or a fresh cell, press Δ, then measure the others. The display shows how far each one is off.
• Watch drift: press Δ at the start, and the display shows how much a voltage has moved as a battery settles after charging or a supply warms up.

HOLD and AutoHold

HOLD (a short press) freezes whatever is on the display, and H shows. Press it again to release.

AutoHold (hold the button for a second; A-H shows) is smarter, and it's one of the best features on the meter. It shows live readings while you measure (Brymen calls this Real-Read), catches the last steady one, and keeps showing it after you take the probes away. Hold the button for a second again to turn it off. It works on volts, VFD volts, current, resistance and continuity.

The details, from Brymen's manual:

• It only acts on significant readings: more than 5% of the range on volts and current, or anything that isn't OL on ohms. Below that it shows dashes.
• It adds up to ±50 digits to the normal accuracy.
• Touch and lift both probes at the same time. With only one probe touching, the meter can latch a stray floating reading.

Where: anywhere you can't watch the display, such as behind a PC, inside a car's fuse box or up a ladder, and runs of quick measurements: a box of batteries, a strip of resistors, a row of terminals. Each one beeps when it's caught, so your eyes can stay on the probes.

REC: maximum, minimum and average

Press REC to start recording; R and MAX AVG MIN show. From then on the meter keeps the highest, the lowest and the running average of every reading, and beeps each time it sets a new high or low. Press REC again to step through the stored MAX, MIN and AVG, then back to the live reading. Hold REC for a second to stop. Auto power-off is turned off for as long as it's recording, so you can leave it overnight; fit fresh batteries first.

REC is fast, but it doesn't see everything. A change has to last long enough to be measured:

The uncertainty figures assume you've locked the range with RANGE, so lock it before you start. For anything faster than these, use CREST.

Where: how low a car or UPS battery sags overnight; the overnight high and low in a comms cupboard or a fridge (with the thermocouple); the lowest voltage a supply reaches while a device boots, as long as the dip lasts 300 ms or more. AVG gives a fair average current for something that switches on and off slowly, like a 12 V camping fridge's compressor cycling on and off. Brymen only specifies REC for changes lasting 300 ms or more on DC, so for a device that wakes in bursts of a few milliseconds, AVG isn't reliable.

~Hz: frequency on volts and current

On AC volts, VFD volts, DC volts, AC+DC volts and every current function, press ~Hz and the meter shows the frequency of the signal instead of its size. Hold ~Hz for a second to go back. (For logic signals, use logic Hz on the mV position.)

The meter only counts a cycle when the signal crosses a trigger level, set by the range you were on when you pressed ~Hz. That's why Brymen's advice is to measure the signal on autoranging first, then press ~Hz, so it starts at the right level. Each further short press of ~Hz steps to the next level:

If the frequency jumps about, the meter is counting noise: step to a less sensitive level. If it reads zero, the signal isn't reaching the trigger: step to a more sensitive one. Each range needs at least this much signal (sine wave RMS) and covers this band, at ±(0.05% + 5 digits):

Where: the output of an AC plug pack or a transformer (50 Hz in Australia), a signal generator or a test tone, the output frequency of a motor drive (with VFD on), and the frequency of an AC current through a load.

EF: the live-wire detector

Press EF and the meter becomes a non-contact voltage detector: it senses the electric field around a live mains conductor through the insulation. It starts at high sensitivity, EF-H; press EF again for low sensitivity, EF-L, if high is picking up everything. Field strength shows as dashes across the display and a beep that changes with it. Hold EF for a second to leave. No test leads are needed. Brymen's operating notes and drawing put the antenna along the top right corner of the meter (its specifications page says the top left), so start with the top right.

It detects 50 and 60 Hz fields only. How: first hold the meter against something you know is live, so you know it's working and which corner responds best; then move that corner slowly along the cable you're checking.

Where: is this power board or extension lead live? Which lead in a bundle is the live one? Where's the break in an appliance cord? With the cord plugged in and switched on, run the meter along it: the indication stops at the break. Only do this if the insulation is intact; a cord with visible damage shouldn't be plugged in at all. Have it repaired or replaced.

What it can't tell you. It doesn't detect DC, shielded cable, or wiring inside metal conduit, and a field can be weak where cables run deep or are partly blocked. No indication doesn't mean dead. Treat EF as a quick pointer, never as proof that something is safe to touch.

Brymen also describes a more precise single-pole method for telling a live conductor from an earthed one: one test lead in COM, its probe touching the bare metal. That means touching mains conductors, which is work for a licensed electrician, so we don't.

CREST: fast peak capture

Press CREST and the meter catches the instantaneous peaks of a voltage or current, the highest and lowest points of the waveform itself, as brief as about a quarter of a millisecond. C and MAX show. Press CREST again to swap between MAX and MIN; it beeps when it catches a new one. Hold CREST for a second to leave. It works on the volts and current functions, and auto power-off is off while it runs.

Two trade-offs: the display drops to 6,000 counts (one fewer digit), and Brymen adds ±100 digits to the accuracy, for changes lasting more than 0.35 ms.

CREST or REC? REC records the meter's normal readings, each one taken over a fraction of a second, so short events get averaged away. CREST catches the actual peak of the waveform. Use REC for trends over minutes or hours; use CREST for anything over in a blink.

On AC, MAX shows the positive peak and MIN the negative one. For a clean sine wave each is about 1.414 times the RMS reading: a 24 V AC plug pack reading 24.0 V peaks at about ±34 V. Much more than that means a distorted waveform or spikes.

Where: the switch-on surge of a 12 V motor, pump or gadget on a low-voltage supply (in series on the A socket; surges can be many times the running current, so mind the 10 A and 20 A limits); the lowest point of a car battery's voltage while the engine cranks; spikes when a relay, solenoid or motor switches off; and whether an AC adaptor's peaks match its rating.

Power-on options: the hidden settings

Hold one of these buttons while you turn the dial from OFF to any position, and keep holding until the message shows:

The Δ note. The manual lists Δ twice: it shows the firmware version, and it also shortens auto power-off to about 8 seconds, a mode Brymen says is for factory inspection. So after you've read the version, turn the dial to OFF and back on normally.

Locking temperature to °C (or °F):

1. Hold EF while switching on, to enable both units (C-F).
2. Turn to the temperature position and press SELECT until it shows °C.
3. Switch off. Hold CREST while switching on: the display shows C, and SELECT no longer changes the unit.

Auto power-off and the backlight

After a spell with no button presses or dial turns, the meter switches itself off to save the batteries. The manual gives the time as about 30 minutes in its operating notes and 15 minutes in its specifications, and Brymen's datasheet says it stays on while you're measuring. It's off automatically during REC and CREST, and for the session if you switch on holding SELECT. To wake it, press SELECT, or turn the dial to OFF and back.

Always turn the dial to OFF when you're done. Even asleep, the meter still draws about 15 µA, which slowly flattens the batteries.

The backlight turns itself off after about 16 minutes without use. Hold SELECT for a second to turn it back on.

Looking after it

Batteries

The BM786 takes three AAA cells (1.5 V, IEC size R03). Alkaline, lithium and NiMH rechargeables all work, according to the EEVblog edition of the manual (Brymen's datasheet lists alkaline only). The battery symbol comes on when the three together drop below about 3.7 V, so with NiMH cells, which sit at about 3.6 V together, expect to see it early. The meter draws about 8 mA, or 10 mA on the AC and AC+DC functions.

1. Turn the dial to OFF and take the leads out.
2. Undo the two captive screws on the battery compartment on the back.
3. Lift out the battery cartridge, replace the cells, put it back, and do up the screws.

If you won't use the meter for more than 60 days, take the batteries out and store them separately.

Fuses

Each current socket has its own fuse, and both are ceramic high-breaking-capacity types rated at 1000 V (the faceplate says "HBC fused"; we explain why that matters in our first BM786 page):

Signs of a blown fuse: a current range reads zero, or close to it, on a circuit that's obviously drawing current, while the other current socket still works. Volts and ohms don't go through the fuses, so they keep working either way.

Replacing one, from the manual:

1. Turn the dial to OFF, disconnect from any circuit and take the leads out. Never use the meter with the case open.
2. Undo the six captive screws on the back (two are under the tilt stand).
3. Lift out the battery cartridge, then undo the two captive screws underneath it.
4. Lift off the upper housing and replace the fuse.
5. Refit the upper housing with the dial pointing at OFF, then the two screws, the battery cartridge and the six screws.

Replace a fuse only with one of the parts Brymen lists above. A cheap glass fuse that fits isn't a substitute.

Firmware

Hold Δ while you switch on to see the version; the last two digits are the version number (for example, 78612 is version 12). The EEVblog edition of the manual lists two changes:

• Version 11: continuity changed from latched to non-latched.
• Version 12: continuity threshold lowered from 270 Ω to 40 Ω.

The manual gives no way for owners to update the firmware. Remember to switch off and on again after checking (the Δ note).

Calibration, cleaning and storage

• Calibration: the accuracy figures hold for one year after calibration, and Brymen recommends calibrating once a year to keep them.
• Cleaning: wipe the meter and leads with a damp cloth and mild detergent. No abrasives or solvents. Let it dry fully before use.
• Where it lives: it works from −20 to 55 °C, below 2000 m, indoors. Store it between −20 and 60 °C with the batteries out if it'll be a while.
• Warranty: Brymen's manual gives one year from purchase, not covering fuses, batteries, accessories or a meter that's been misused.

Where Brymen's documents disagree

Brymen's documents cover three models, and a few details don't agree (two items below also draw on the EEVblog Store's listing). Here's what we found, and what we've gone with:

• The drawings are of the BM789. They show an Auto-V/LoZ dial position, dBm, a second thermocouple input (T1-T2) and a 4 to 20 mA loop setting. None of those is on the BM786.
• The EEVblog edition leaves out the AC volts section. Brymen's three-model manual has it: on that position, SELECT steps from AC volts to VFD volts (dBm is the BM789's only).
• Bandwidth. The datasheet's cover says 100 kHz true RMS. That's the BM789; Brymen's own feature table lists the BM786 at 7 kHz, and its accuracy tables stop there.
• Auto power-off: about 30 minutes in the operating notes, 15 minutes in the specifications.
• EF antenna: "along the top-right corner" in the operating notes and drawing, "top-left end" on the specifications page. We've gone with the top right.
• Continuity threshold: 100 to 420 Ω in the manual's specifications, 20 to 200 Ω on the datasheet, and 40 Ω from firmware version 12 in the change log.
• Holding Δ at switch-on is listed for both the firmware version and an 8-second auto power-off.
• Crest timing: 0.25 ms in the operating notes and the datasheet, 350 µs on the EEVblog Store listing, and accuracy specified for changes over 0.35 ms.
• The 400 mA fuse: 6 × 32 mm in the manual; the EEVblog Store sells its pack as 6 × 30 mm. Brymen's specifications also ask for a breaking capacity of 30 kA or better on this socket, but the ASTM HV620 it lists as an alternative (the fuse in the store's pack) is rated 10 kA.
• VFD accuracy: the table gives ±(4% + 50 digits) from 10 to 200 Hz, but its footnote says accuracy falls from ±(2% + 50 digits) at 200 Hz.
• Batteries: the EEVblog edition allows alkaline, lithium and NiMH cells; the datasheet and the three-model manual list alkaline only.

We'll check these on our own meter and note what it actually does on our BM786 page.

Common questions

Sources

Brymen

• BM786 user's manual, EEVblog edition (January 2021): every function, button, power-on option, specification, battery and fuse procedure, and the firmware change log. link. Checked 21/10/2026.
• BM789 / BM786 / BM785 user's manual (three-model edition): the AC volts and VFD section missing from the EEVblog edition. link. Checked 21/10/2026.
• BM780 series datasheet: feature table by model (BM786 AC bandwidth 7 kHz; nS and one thermocouple input on the BM786; no dBm, LoZ or 4 to 20 mA). link. Checked 21/10/2026.

EEVblog

• EEVblog Store, EEVblog BM786 Multimeter: features, what's included, links to the manual and datasheet. link. Checked 21/10/2026.
• EEVblog forum, "BM786 continuity beep not latched": hold Δ at switch-on for the firmware version; how latched and non-latched continuity sound. link. Checked 21/10/2026.
• EEVblog forum, "BM786 input legend": the symbol above the current sockets is the BeepJack warning. link. Checked 21/10/2026.

Digital Greenhouse

• Our own BM786: the dial order, button labels and display, from the meter and our photo above.