Disabling Standby Lights

Light emitting diodes (LEDs)

Once upon a time, appliances had real off switches. Today, many appliances are never totally off. Sometimes this is to maintain an internal clock (a lame excuse as relatively inexpensive backup memory capacitors can serve as micropower sources) or more commonly, to allow a signal from the remote control to be able turn the appliance fully on.

Somewhere along the line, companies starting putting "standby" lights on their products. I really dislike this "feature". To me, it's like the appliances are constantly begging to be unplugged. Perhaps this is acceptable practice on products that come with a hardware off switch, but most don't (perhaps a topic for another rant). This is especially problematic for appliances that are in a bedroom because the lights can be distracting to people who are trying to sleep. The problem is so bad that many product reviews now mention a "bedroom safe" (i.e., standby light free) feature. In other cases, the standby or power light is so bright that it can interfere even with daytime TV viewing if the offending light is located close to the screen.

caution sign

Note: In what follows, it is assumed that the person doing the modifications has a basic understanding of electronics, soldering skills, and safe electrical practices. The example shown is typical, but may not be representative of every appliance. Always ensure that the device is unplugged before opening the case. The modifications discussed here will almost certainly void the product warranty and if done improperly, can result in property damage, injury or even death. This information is offered as-is without any warranty. User assumes all risk.

If you know something about electronics and can use a soldering iron (or know someone who does) you don't have to put up with an annoying standby light - you can disable it electrically. (If simply taping it over on the outside is too crude for you, LOL.) Here's how.

Most all standby/power lights these days are just common light emitting diodes (LEDs) that require just a few milliamps of current. If the LED serves as only a standby light, then it is a straightforward task to simply disconnect it by cutting the wire or printed circuit board (PCB) trace leading to it. However, things get more complicated when the same LED also serves as the power on light, the latter feature generally being desirable. An LED (or more correctly, two LEDs contained within a single part housing) can be constructed to produce two different colors depending on the polarity of the applied voltage by connecting two internal LEDs in parallel, but in the opposite direction so that only one of the two LEDs is forward biased at a time. This is the case of color-changing LEDs that have only two terminals. With a three or more terminal package, each of the internal LEDs can be operated independently (including simultaneously) with one terminal serving as a common which usually is grounded (common cathode with a positive power supply).

For two terminal devices that are controlled by reversing the polarity, one LED can be disabled by putting an external diode in series to prevent current flow under one polarity, but still allow it for the other. The added diode will cause a small voltage drop for the operating LED, but this is usually not an issue. Disabling a single LED in a three or more terminal package is simply a matter of disconnecting the correct lead.

An Illustrated Example

Here is an example of a modification I did to my Coship N9988T digital TV tuner box. I generally like this tuner box, and, ironically, this model does have a hardware power switch. However, it has a problem in that the power and standby lights (green and red, respectively, from the same LED package) are very bright. So much so, that it is distracting during daylight TV viewing. Well, I couldn't put up with that. So, I rolled up my sleeves and went to work opening the case.

Figure 1 shows the front panel PCB. The standby/power LED, outlined in red, is a three terminal part. Tests with a voltmeter showed that the top terminal is the anode of the green power LED and the bottom terminal is the anode of the red standby LED. The middle terminal is the common cathode.

The printed circuit board

Figure 1: The front panel printed circuit board showing the power/standby LED and trace cuts.

Using a razor blade knife, I cut the two traces leading to the anodes which are outlined in blue in figure 1 as well as in the closeup in figure 2. This isn't the most pretty of work of mine; perhaps it would have been better to use an engraver bit with a Dremel tool. It is important to remove any stray copper pieces least they produce a short. On this model, an alternate approach would have been to unsolder the two wires on the lower right that feed these traces and, therefore, avoid the need for any cutting.

The LED and cut traces

Figure 2: A closeup of the cut traces.

I then soldered in a 330 ohm 1/2 watt resistor to restore power to the green power LED, although at a reduced level to lower the brightness. The best value is a subjective matter and so some trial and error is involved. As the LED draws only about 3ma, I could have used a 1/4 watt or even a 1/8 watt resistor.

The dropping resistor

Figure 3: A 330 ohm dropping resistor to dim the power light.

If I ever want to restore the previous behavior, it would be a simple matter to solder in two wire jumpers to repair the trace breaks. After putting the case back together, I can now enjoy watching TV without having to endure a blinding green power light and the standby light is no more.