I have been looking at google images of cylindrical smd resistors, but they don't look like the ones on my board. So my question is: What component is this?

Long story:

This board is a 230VAC to 11.8VAC converter for a lamp which does no longer output 11.8VAC but rather drops down from 8VAC very quickly(~1sec) to 0VAC and I at least try troubleshooting it. The mystery components mentioned also behave strangely when measured by a multi-meter (they each give different resistance values even when measured from different sides ranging from 1kOhm to 150MOhm) enter image description here

  • \$\begingroup\$ I doubt those are the issue. It is the other components in the circuit your meter is being affected by. Yes this are MELF resistors. I guess they also could be inductors though... \$\endgroup\$ – MadHatter Jan 4 at 17:33
  • \$\begingroup\$ You're measuring them in the circuit... that can't work. There's diodes and transistors and other circuitry in parallel... \$\endgroup\$ – Marcus Müller Jan 4 at 17:39

Component marking

These packages are called MELF (metal electrode leadless face). They're usually used for resistors and diodes.

The fact that there are only two color bands/rings makes them less likely to be resistors.

See Electronic color code on Wikipedia.

The missing third ring could be interpreted as zero (black), making the red-yellow component a 24 Ohm resistor.

Vishay uses two-ring color codes to mark their diodes. Here's an example:

Vishay document showing markings of a MELF package for diodes


That would make the red-yellow component a BYM11-series 400V diode.

To be sure you should measure the components out-of-circuit.

In-circuit measurement

When measuring components in-curcuit, you should be aware that other components might influence your measurements.


  • low value resistances parallel to diode-under-test make them appear short-circuits
  • capacitors parallel to resistor-under-test make them look short-circuit with rising resistance

These are examples, there are more combinations.

Components are best tested out-of-circuit to be sure. When measuring in-circuit cannot be avoided keep the above in mind and suspect components to be a certain type.


When measuring components that connect to mains make sure you wait long enough to bleed existing charge off of capacitors. You might use Low-Z mode on a multimeter to test such capacitors and help discharging them using the low input impedance. Be aware of dielectric absorbition

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