Test with a multimeter

555 timer

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Now: VCC to GND: internal resistors

5 V CircuVanta 6000 counts · auto range DCAUTO•)))HOLDFUSE− HOLD LIGHT OFFV⎓V~Ω•)))FmA⎓ mA400 mACOMVΩ GND 1 GND TRIG (trigger) 2 TRIG OUT (output) 3 OUT RESET 4 RST CTRL (control) 5 CTRL THR (threshold) 6 THR DIS (discharge) 7 DIS VCC 8 VCC
Pin 1: GND (GND) Pin 2: TRIG (trigger) (TRIG) Pin 3: OUT (output) (OUT) Pin 4: RESET (RST) Pin 5: CTRL (control) (CTRL) Pin 6: THR (threshold) (THR) Pin 7: DIS (discharge) (DIS) Pin 8: VCC (VCC)

Red probe Not connectedBlack probe Not connected

Hold the probe and drag it to the tip of a leg. Tapping works too: first pick the probe, then the leg.

Set the range to Ω (resistance).

Test setup: Setup: it powers with 5 V; wired as an astable with R1 = 1 kΩ, R2 = 47 kΩ, C = 100 nF. Press the “Power on” button.

Measure step by step

Between the supply pins (VCC-GND) of 555, about 15 kΩ is read because of the 3 resistors of 5 kΩ inside. A short circuit pulls this value to zero. In the setup, 555 runs astable: the output switches on and off continuously and the multimeter shows only the average, about half the supply. The multimeter cannot measure the IC’s temperature, behaviour under load or speed: this test only shows that there is no short circuit and that the setup gives the expected voltages. A good result means “it could not be proven faulty”.

Isolate the IC from the circuit and measure it unpowered. Do not use the Ω range on a pin that has voltage on it.

  1. 1VCC to GND: internal resistors
  2. 2Power on: VCC voltage
  3. 3Power on: CTRL pin
  4. 4Power on: average of the output
  5. 5Power on: supply current