SMD code search: identify a part by its marking
120 µF capacitor. 1 part is printed 127K.
127K is a capacitor marking
120 µF
120 µF capacitor, 10%
12 followed by the multiplier 7, in picofarads: 120 µF. Printed this way on film and larger ceramic capacitors; small chip ceramics are usually not printed at all. K is the tolerance, ±10%. The same marking also reads as 127 kΩ on a resistor, and nothing in the code says which; the body of the part does.
Other readings of the same characters, most likely first
- 127 kΩ resistor
Check it with a meter
Lift one end and measure it on a capacitance range. A good one reads close to 120 µF. In circuit the meter also sees everything connected across it, so the reading means little until it is out. A failed one usually reads near 0 Ω, or a steady low resistance, on the ohms range, often from a crack. On the board a shorted capacitor shorts its whole rail. A failed reading does not change what to fit: the marking still says 120 µF.
On a transistor or diode body (SOT-23), 127K is a part code instead. Those parts are listed below.
The only part printed 127K in our tables
MTN127KN3
- What it is
- N-channel MOSFET
- Maker
- CYStek
- Package
- SOT-23
- Pins
- 3
- Details
- 600 V, 0.04 A N-channel MOSFET
- Source
- Manufacturer datasheet
Is it dead?
Diode range, part lifted. Test drain to source first, then short gate to source and test again.
Working, it reads
Red probe on the source, black on the drain: about 0.4 to 0.9 V, the body diode. Open the other way. The gate reads open to both other pins, both ways.
Dead, it reads
- Drain to source the same both ways, near 0 V with a continuous beep, and still so after shorting gate to source: shorted. The classic failure.
- The gate reads low to source or drain: gate shorted. Often all three pins end up shorted together.
- No body diode at all: failed open.
- On the board
- the gate usually has a resistor to the source, so gate to source reads that resistor, which is not a fault. A drain short can be the load. Lift a leg to be sure.
- Compare:
- If an identical part sits elsewhere on the board, measure it the same way: that is what this one should read.
- Watch for:
- The diode range can charge the gate enough to turn the part on, and then drain to source reads near 0 both ways on a good part. Short gate to source and test again before you condemn it.
A dead part still carries its marking. A short or an open says it has failed, not that it is a different part.
Was it this one?
Did you find your part?
Try Tech free for 30 days. You need a card to start. Unless you cancel during the trial, Tech then costs €12.00 a month plus VAT. See the plans
One code, several parts
Marking codes are not unique. In the standard code book, 6H on a SOT-23 is an NPN transistor, a varicap, an N-channel JFET, two digital transistors, a 3.6 V voltage detector: six parts from five makers. So a search on WhatSMD (What SMD) shows the parts we hold under that code and under codes easily misread as it, with only the columns that tell them apart.
- NPN transistor
- Varicap
- N-channel JFET
- Digital transistor ×2
- 3.6 V voltage detector
When more than one is left
Tap Help me choose. Up to 4 quick answers: whether the part has failed, then what separates the parts left. Those get ranked with the reasoning and a test that settles it. That uses one identification: 2 a month are free without an account, and 3 with a free account.
When you cannot read it
Tap the camera in the field. We read the characters, keep the ones we are unsure of, and search every reading. A photo too soft to read is turned back on your phone first; if it is the only one you can get, you can still send it.
Get the app
The same search on your phone, and a camera with a light, zoom and tap to focus for a marking you cannot read. Sign in with your email address to use the same account.
- Coming soon to the App Store