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Know Why 1/2 Strand Of Cdi Leds Barely Come On?


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2 years ago I bought three cases of CDI's 100ct 5mm minis during their great pre-order sale. For the most part I have been been very happy with them.

Recently though one of the strings has started acting weird. Half of the string lights up fine, the other half is very dim, but you can see a VERY little amount of light coming through. This seems to be effecting the whole half of that string. I cannot figure out why this would be, but it makes the house look odd to have it off like that. The rest of the strings that are chained off of it are lighting fine (both before and after the light), so I don't think it is a power issue, but I don't know what it could be (this is a static string of lights). Is there anything I can do to revive the string? Is it possible something has gone kaput in the little molded blobs that are at the end and in between the two sections of the light? I don't mind hacking it if there is something internal that needs to be done if I can save the light string cheaply.

I contacted Creative Displays, but they didn't know what to do. A second one started doing this last night and I would hate to pitch these strings (very few hours and not inexpensive) so quickly if I can just make them function again.

Any of youall had experience with something like this?

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Yes,the cause could be a single led.

You can find out which one/ones are bad and cut them out and replace them.

With sealed strings you will need a sacrificial string to use for fixing the other strings.

You can get shrink tubing in the same color as the wire (green/white) and solder in new led's.

I have fixed about ten so far. I had two that had the same issues you describe and it ended up being one to three bad leds on that section.

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Also could be the rectifier. This usually is the big blob on the strings. If you have 2 blobs then the one on the end nearest the bad half could be bad. The led keeper would verify if your leds are good and if they are then your rectifier is bad.

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Hmmm, all very interesting.

So with a bad LED, all 50 could still semi-light (even the bad one)? I guess then I have to take the LED Keeper (I'll need to get one) and test every single bulb, right? Since I haven't used the LED keeper before, I assume bulbs that are not the culprit will glow fine with the Keeper?

If it is the rectifier, I assume that means all 50 bulbs will pass the above test (leaving the rectifier as the culprit)? Is there a parts recommendation for replacing them?

Thanks!

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If it is the rectifier it would be very difficult to remove all the coating to try to identify the components in the rectifier to replace it. But you would have spare leds for repairing another strand. If it is a led, there is a couple of resistor parts included with the led keeper you can replace the led with to make the rest of the string work.

Edited by keitha
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Just to throw this out there........ IMO, the odds of a single bulb causing a string of 50 to be dim is slim to none. LED bulbs almost alway fail, rather than go dim. It is almost surely the rectifier. That can be replaced if you are VERY handy, but probably not repaired as they are 'potted' in plastic.

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+1 to rstehle

You can take a niddle and pierce the wire directly after the rectifier blob and then pierce the return wire with another needle (smaller the better)

do this on a good working string then on the one needing work set your amp meter to dc and test both strings

the power should be the same. My bet is you are dropping 1\2 a volt or so through the dim set

if so you could make your own rectifier or as mentioned above take one string and use it for repairs

I will also +1 for the LED keeper pro to make the repairs

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How does the LED Keeper check the bulbs? I assume you end up piercing a wire before/after a bulb and then it lights it up? Then if all is good, you move onto the next one. That about right? So to rule out LEDs I would need to check all 50?

Also, how does the LED go "bad" yet partially light?

If it is the rectifier, can I just replace it (I know it won't be in a similar green blob, but I would think I could drop something inline)?

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You can view a video on their website. It has been awhile but I think you can start about 1/2 way down the bad portion of the string and see if that half works ect. until you narrow it down to the bad bulb. Not all rectifiers are the same. Different colors use different resistors. Longer strings may use capacitors to do voltage doubling. I had to replace all rectifiers on the infamous cdi strings a few years ago (manufacturers problem not cdi's fault). Luckily there were people smarter than me who figured out what values all the components should be to allow me to make my own rectifiers.

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I bought an LED Keeper and hope to revive these strings after Christmas, thanks for the tips!

 

I found this thread on the rectifiers:

but the link in it didn't work.  Anyone have the pdf or know the values for a string of multis?

 

DSE: For testing the rectifier, you are saying to look at the DC voltage while plugged in when poke just after the blob and at the end of the return?  A 0.5Vdc difference between a good set and a bad set would be enough to dim my LEDs?

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in testing them I would be looking for a change in values from the good one to the suspect one (rectifiers - Blob)

With these leds a very small drop would be a couse for half your string being not as bright

at this point you are just eliminating potentials

Your issue could be a bad led but my thinking would be more in the rectifier

.5 is a signifigant number

The other side of the coin is normally in these sorts of issues it either works or doesn't kinda of like you really can't be half pregnant

Please post what you find very interesting problem (sorry you got stuck with it)

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  • 3 months later...

I finally got around to testing and fixing my FIVE bad strings and in every case it was a bad bulb.  I used one of the LEDKeeper pods to replace the first one, then after that I soldered a 330 ohm resistor in-line to replace the missing bulb on the other four.  Thanks to all for the tips and advice.  The LEDKeeper definitely saved me time and money, it is just a shame that i had to fix so many 2 seasons in!

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