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

[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 :)

[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.

[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

[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.

[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 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!

[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 =)

[ArchaicAmusements]

2.7v and 100mA is definitely too high. I'd say that led would be about 1.8v at 50mA. (lower is better as it increases lifespan) Nice explanation other than that. Only thing I disagree with was using the variable PSU. You can find the forward voltage using your multimeter on diode test. The value returned (in mV) is the forward/working voltage for the LED. Some won't have enough current however (if the LED doesn't light).

[MrAns98]

Hi,very nice tutorial,and very nice multimeter, what brand and type is.

[DrCassette]

@MrAns98

It's a UNI-T UT70A.

[MrAns98]

@DrCassette Good multimeter,how much you paid for it.

Nice videos keep making more,I realy like all of your vids..

[DrCassette]

@MrAns98

I don't remember, maybe 30€, it was a special offer.

[TwinMillMC]

Very informative video indeed. Thanks for posting it. What do you think of the comments posted below this one? Is your voltage estimation for these LED's correct?

[DrCassette]

@TwinMillMC

It is correct. See my comments below.

[THEtechknight]

no, it will not. those type of LEDs have a maximum rated current of say 25ma. Dont want to exceed this. 25ma should put your required voltage roughly at 1.9V.

[DrCassette]

@THEtechknight

@TehMG

I too was surprised about how much this LED would take, but it is of course a super bright one. I turned the power supply up until the current started rising exponentially (rather than linear), turned it down a bit and ended up with 2,7V. So that should be correct.

[TehMG]

I predict that LED won't last long. Somewhere around 20mA is typical for these indicator LEDs.

Red LEDs typically have an operating voltage of 1.8 to 2.2V. At 2.7V you're definitely overdriving the LED.

[DrCassette]

@TehMG

I too was surprised about how much this LED would take, but it is of course a super bright one. I turned the power supply up until the current started rising exponentially (rather than linear), turned it down a bit and ended up with 2,7V. So that should be correct.

[TheMrmagnetophon]

An Excellent video DR. keep up the hard work :-)