Diode mode
Diode mode is a multimeter function that sends a small test current (usually ~1 mA) into a circuit and measures how much voltage is needed for that current to flow.
This measured voltage drop (like 0.300V, 0.450V, 0.600V) is called the diode value.
Technicians prefer diode mode over resistance mode because smartphone motherboards contain complex semiconductor networks, where resistance readings are unstable. Diode values are steady, repeatable, and easy to compare, making fault diagnosis faster and more accurate.
🔴 Why is the Red Probe Placed on Ground?
Most IC input pins and ESD protection circuits inside smartphones have diodes connected toward ground (anode at GND, cathode on the line).
To measure the diode correctly in forward direction, the multimeter’s positive output must be on ground:
- Red probe → Ground
- Black probe → Test point / line
Reversing the probes usually gives OL / 1.1V–1.2V readings because the diodes are reverse-biased.
(Some iPhone lines are exceptions with reverse polarity.)
✅ Typical Diode Values
| Condition | Diode Reading | Meaning |
|---|---|---|
| Normal line | 0.200V – 0.700V | Healthy |
| Low diode value | 0.050V – 0.200V | Leakage / semi-short |
| Zero value | 0.000V – 0.010V | Full short to ground |
| High value / 1.2V / OL | ~1.100V – 1.200V | Open line / broken track |
Tip: 1.2V in diode mode usually means no path to ground — the meter reaches its maximum test voltage because the line is open.
🛠️ Why Diode Mode is Safe
- The multimeter sends only a small current (~1 mA)
- Safe for CPUs, PMICs, ICs, and other sensitive components
- High enough to detect shorts, leakage, or open lines reliably
Diode mode is one of the most effective tools for smartphone motherboard repair, helping technicians quickly identify shorts, leakages, open lines, and verify motherboard health accurately.
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