SMD code 77s
Marking codes are not standardised, and the same code is reused by unrelated makers for unrelated parts. Below is every part in our tables printed with it, and any printed with a code that is easy to misread as it, from the manufacturers' own marking tables and published code lists.
77s on a chip resistor
61.9 Ω
61.9 Ω resistor, 1%
EIA-96 precision code: 77 selects 6.19 from the E96 series and S multiplies by 10. These are 1% parts. The trailing S is also used as a decimal point, so this could instead be 77 Ω. Measure it before fitting a replacement. If it has failed and reads open or high, that settles nothing: measure the same position on a working board.
Check it with a meter
Lift one end and measure across it. A good one reads 61.9 Ω within 1%. Measuring it in circuit reads the parallel combination of everything around it, which is almost always lower, never higher: well above 61.9 Ω on the board is a fault. Open, or well above 61.9 Ω, means it has failed: burnt, cracked or corroded. That does not change what to fit: the marking still says 61.9 Ω. A burnt resistor usually means the part it feeds drew too much, so find that before fitting a new one.
On a transistor or diode body (SOT-23, SOT-323, SMB), 77s is a part code instead. Those parts are listed below.
3 parts are printed 77s
Not sure which one you have?
Answer up to 4 quick questions and these 3 parts are ranked, with a meter test that settles it. It works on a dead part too.
BAS70-07SOT-143Schottky diode, 4 pins, InfineonSchottky diodeSOT-1434 pinsInfineon
- What it is
- Schottky diode
- Maker
- Infineon
- Package
- SOT-143
- Pins
- 4
- Details
- 0.07A, 70V, Surface Mount Small Signal Schottky Diodes
- Source
- Published code list
Is it dead? The meter test is below: Schottky diode.
BAS70-07WSOT-343Schottky diode, 4 pins, InfineonSchottky diodeSOT-3434 pinsInfineon
- What it is
- Schottky diode
- Maker
- Infineon
- Package
- SOT-343
- Pins
- 4
- Details
- Si-diode: Dual, Schottky, GP, 70V, 70mA, Vf<1V(15mA), <100ps
- Source
- Published code list
Is it dead? The meter test is below: Schottky diode.
XC6111B324MRSOT-23-5Voltage supervisor, 5 pins, TorexVoltage supervisorSOT-23-55 pinsTorex
- What it is
- Voltage supervisor
- Maker
- Torex
- Package
- SOT-23-5
- Pins
- 5
- Details
- CMOS-IC: VDet 2.4V, -MR, -Reset PPO, Wt=100ms, Rt=25ms
- Source
- Published code list
Is it dead? The meter test is below: Integrated circuit.
Is it dead? One meter test per kind
Parts of the same kind are tested the same way, so each test is here once. Each part above points to its own.
Schottky diode
Diode range, part lifted or one leg off the pad. Red probe on the anode.
Working, it reads
About 0.15 to 0.45 V anode to cathode, roughly half a silicon diode, and open the other way.
Dead, it reads
- The same reading both ways round, near 0 V with a continuous beep or the same middling value: shorted.
- A reading the wrong way round as well: leaky.
- Open both ways: failed open.
- On the board
- this is a first look only: the meter reads every path between those pins, and a short can be a neighbour. Lift one leg before you condemn it.
- Compare:
- If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
- Watch for:
- A large Schottky can read about 0.1 V forward and beep like a short, and leaks a little the wrong way when good, more when warm. It is shorted only if it reads the same both ways. Measure it cold, beside an identical cold one.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
Integrated circuit
Voltage with the board powered; ohms from each pin to ground with it off.
Working, it reads
Supply pin at its voltage and the output doing what the datasheet says. Readings between pins depend on the part.
Dead, it reads
- A pin near 0 Ω to ground or to the supply pin where an identical part does not read that: failed short.
- Supply present, output stuck: failed, or its load has.
- On the board:
- A pin shorted to ground on the board can be anything on that net. Lift the pin to be sure.
- Compare:
- The surest reference is the same IC on a working board, measured pin by pin.
- Watch for:
- Its protection diodes can read like junctions between pins, even like a transistor. That proves nothing either way.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
Printed with a code easy to misread as 77s
One character differs, and it is one that is easy to confuse under a lamp. Each code has a page of its own.
Codes that begin with 77s
For a marking with its end worn or burnt off. Each code has a page of its own.
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