DCW: How to replace light bulbs with LEDs - instructional video!

In this episode of DrCassette's Workshop, I' going to show you how to replace a light bulb with an LED and how to calculate the value of the series resistor.

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[yeoldeengineer]

Oh, and I wouldn't be surprised to see a series resistor already present for an indicator bulb. (It certainly would be in this case, as small bulbs tend to be 24, 12, 8 or 6.3 V jobs.) That one would obviously have to be considered, too.

[DrCassette]

@yeoldeengineer

There is in fact a resistor on the circuit board already, pretty similar to the one I put in :)

[vwestlife]

Does the "U" in your Ohm's Law calculations stand for a German word meaning "voltage"? I learned it as "E", for "electromotive force" -- a fancy way of saying voltage. But a lot of times people simply use "V" instead.

[DrCassette]

@vwestlife

I don't know what the U stands for - I learned it this way. I also learned that E stands for the strenght of an electric field. Seems like all these letters are not as international as I thought :D

[yeoldeengineer]

One caveat to be aware of in this special case: While this unit (it's the Onkyo Y-200D, I guess) looks old enough to contain a discrete stereo decoder with a transistor able to sink 100 mA, several stereo decoder ICs are NOT. Some early ones are rated for as little as 40 mA and can actually be (and have been) burned out by inappropriate replacement bulbs.

100 mA does seem a bit high for an indicator LED, particularly if it's a super-bright job. (Normally it's ~20.) 270 mW is a bit toasty, too.

[TheChipmunk2008]

@vwestlife Could be the difference between that and ground reference maybe? It seems likely, as the first references to it I remember were on European imports to the UK, it was probably standard in other parts of the EU much earlier, the UK always lags behind. I may have to do some research on this!

[vwestlife]

@TheChipmunk2008 The one explanation I've seen is that the "U" stands for the German word "Unterschied", meaning "difference". That only makes sense to me in the context of a voltage drop; otherwise almost any of the other electrical measurements could have a difference between one point in the circuit and another!

[TheChipmunk2008]

@vwestlife U is quite normal now, I am not sure where it comes from though. On circuit breakers and so forth you'll see "Un=230/400v" for "Nominal Voltage" etc. Like I for current.. If anyone knows, it would be interesting to find out.

[TheTrueVoiceOfReason]

Another excellent and thorough video.

In case you wanted to know, MPX, as it is used here stands for MultiPleX. That is Stereo MultiPleX, showing when the 19kHz pilot signal is present for decoding into the left and right stereo channels.

[SammyMac]

Very imformative tutorial. I like the calculations also, as will be handy if any blubs go in my 80s hifi systems. Thanks =)