The standard 680 ohm resistor color code is Blue, Gray, Brown, Gold for a 4-band (5% tolerance) resistor, and Blue, Gray, Black, Black, Brown for a 5-band (1% tolerance) resistor. If you are holding a component and need an immediate visual confirmation, look for the blue (6) and gray (8) significant digits, followed by a brown multiplier (×10) on standard carbon film parts.
The 680Ω Resistor Color Code Reference Table
The table below breaks down the exact band assignments based on the global IEC 60062 standard. Read the bands from left to right, keeping the tolerance band (usually Gold or Brown) on the far right.
| Band Position | 4-Band Color (5%) | 5-Band Color (1%) | Numeric Value & Function |
|---|---|---|---|
| Band 1 (1st Digit) | Blue | Blue | 6 |
| Band 2 (2nd Digit) | Gray | Gray | 8 |
| Band 3 (3rd Digit / Multiplier) | Brown (×10) | Black (0) | Multiplier (×10) or 3rd Digit (0) |
| Band 4 (Multiplier / Tolerance) | Gold (±5%) | Black (×1) | Tolerance or Multiplier (×1) |
| Band 5 (Tolerance) | N/A | Brown (±1%) | Final Tolerance Rating |
Standard Variants: IEC 60062 vs. SMD vs. Legacy Mil-Spec
While wire color codes vary wildly by region (NEC in the US, IEC in Europe), through-hole resistor color codes are universally governed by IEC 60062. However, the physical format of the resistor changes how the 680Ω value is represented on the bench.
- IEC 60062 (Global Through-Hole): The universal standard for axial leaded resistors. Uses the Blue-Gray-Brown-Gold sequence detailed above.
- SMD / Chip Resistors (EIA Standard): Modern surface-mount devices abandon color for printed numerals. A standard 3-digit SMD resistor for 680Ω is marked 681 (68 × 10¹). If you are working with precision 1% SMD parts using the EIA-96 code, 680Ω is represented by the code 82B (82 = 681 base value, B = ×10 multiplier).
- Legacy US Mil-Spec (MIL-R-39008): If you are repairing vintage military or aerospace avionics, you may encounter a 5-band or 6-band resistor where the final band does not indicate tolerance, but rather reliability level (failure rate per 1000 hours). In these legacy systems, always verify with a multimeter rather than trusting the color code blindly.
Rows and Bands People Get Wrong
Even experienced technicians misread specific resistor values. When dealing with the 680 ohm resistor color code, three specific pitfalls cause the most misidentifications on the workbench.
1. The 4-Band Multiplier Trap (Brown vs. Black)
The most common mistake is reading a 4-band 680Ω resistor as Blue-Gray-Black-Gold. Readers see '680' and instinctively look for a black multiplier (×1). However, a 4-band resistor only has two significant digits (6 and 8). To get 680, you must multiply 68 by 10. Therefore, the multiplier band must be Brown (×10), not Black. Black is only used as a multiplier in 5-band 1% resistors where '0' is the third significant digit.
2. Heat-Shifted Brown and Black
Carbon composition and older carbon film resistors that have run hot for years often suffer from thermal darkening. A Brown multiplier band can easily bake into a dark, muddy Black, leading you to read the part as 68Ω instead of 680Ω. Conversely, Red (2) and Orange (3) can fade and look identical under fluorescent bench lighting.
3. Reading Backwards on 5-Band Resistors
On a 5-band 1% metal film resistor, the tolerance band is Brown (±1%). Because the first digit (Blue) and the tolerance band (Brown) are both dark colors, it is easy to flip the component backwards. If you read it backwards, you would calculate Brown-Black-Black-Gray-Blue, which translates to a nonsensical value. Always check for the physical spacing gap between the multiplier and tolerance band.
Decision Path: Verifying Faded or Suspect 680Ω Resistors
When markings are faded, scorched, or entirely missing, visual identification is unsafe for circuit repair. Use the following decision tree to safely interpret and replace the component.
| Condition / Symptom | Action & Measurement | Concrete Resolution / Part Pick |
|---|---|---|
| Resistor is out of circuit, bands are scorched/missing. | Measure with DMM in resistance mode. If it reads ~680Ω (±5%), it is functional. | Reuse if functional. If open (OL), replace with Yageo MFR-25FBF52-680R (1/4W 1% Metal Film). |
| Resistor is in-circuit, reads significantly lower than 680Ω. | Parallel circuit paths are skewing the reading. Lift one leg of the resistor from the PCB pad and measure again. | If lifted reading is ~680Ω, the part is fine. If still low, the resistor is shorted (rare) or PCB trace is bridged. |
| Resistor is in-circuit, reads higher than 680Ω or OL. | Resistors fail 'open' or drift high when overloaded. The part is destroyed. | Desolder and replace. Upgrade to a 1/2W variant (Stackpole RNMF14FTC680R) if thermal failure was the root cause. |
| Bands are visible but ambiguous (e.g., Brown vs Black). | Clean the body with 99% isopropyl alcohol. Use a magnifying loupe to check the underlying body color (beige vs blue). | If ambiguity remains, treat as unreadable. Desolder and measure. Default replacement: Vishay MRS25000C6800FCT00. |
When to Use a 680Ω Resistor in Practice
The 680Ω value is a standard step in the E24 resistor series (which includes values like 560, 620, 680, 750). It is not an arbitrary number; it is mathematically distributed on a logarithmic scale to ensure that no matter what target resistance you calculate, a standard off-the-shelf part is never more than 5% away from your ideal value.
The most common practical application for a 680Ω resistor on the bench is LED current limiting in 12V DC systems.
Consider a standard indicator LED with a forward voltage (Vf) of 2.2V and a target current of 15mA, powered by a 12V automotive or solar battery rail. Using Ohm's Law:
- Voltage Drop Required: 12V - 2.2V = 9.8V
- Ideal Resistance: 9.8V / 0.015A = 653.3Ω
Since 653Ω is not a standard E24 value, you round up to the next available standard value to ensure you do not overdrive the LED. The next standard E24 value is 680Ω. At 680Ω, the actual current will be 9.8V / 680Ω = 14.4mA, which safely drives the LED at near-full brightness while extending its operational lifespan and keeping the 1/4W resistor well below its thermal limit (Power = I²R = 0.0144² × 680 = 0.14W).
For any modern prototyping or PCB repair requiring a 680Ω value, default to purchasing 1% tolerance metal film resistors (like the Yageo MFR series). They cost only pennies more per reel than 5% carbon film, offer vastly superior temperature coefficients (typically ±50ppm/°C), and their 5-band color codes eliminate the multiplier confusion inherent to 4-band parts.
