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Thread: Replacing rectifier or blob

  1. #1
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    Default Replacing rectifier or blob

    I have a string of LED's that went dim and some that have part of the string that has failed. I have both the full wave converter and shorter boards. Can I use one of them to replace this to possibly make it work? Experimenting but I don't get the third wire. This is the only circuit board on the string besides the two plugs.

    Thanks
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    Just remember. Wireless is nice. Copper is king!

  2. #2
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    Default Re: Replacing rectifier or blob

    The photo shows two wires on left (A/C hot & neutral) and three on the right (A/C hot/neutral) and one DC, marked + (positive). Somewhere you must have a three wire on left and two on right. It would be marked two for A/C and one DC, marked - (negative). That third wire goes to your LEDs anode. The other end would go to the cathode. What you have is a half-wave string, but with the capacitor in there I wouldn't expect the dimming to be 'nice'.

    This is not the typical way to configure LED strings, but I can work with you on repairing the string with one of your full wave converter boards (if you want to add another wire the length of the string), or with two (halves? of a) full-wave converter boards.

    I gotta find the schematic diagram I once drew up for this, so we can communicate better.

    Jimboha
    Springville, Utah

  3. #3
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    Default Re: Replacing rectifier or blob

    Thanks. I am curious how to wire the boards.

    After taking out the cap and testing it and replacing the diode as a test my wife said, "is it possible one of the LED's is loose"? Well come to find out after probing with my multi meter that was the problem. I grabbed an LED from the drawer and we were in business. This string was just in the kids room so no dimming.

    My next set is full wave commercial set that half is dim. This could be and LED also so I'm on the hunt for a LED keeper on sale.

    But I'm still curious how these full wave converters work.
    Just remember. Wireless is nice. Copper is king!

  4. #4
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    Default Re: Replacing rectifier or blob

    Find the schematic for a full-wave rectifier: 4 diodes in a diamond pattern. Add a resistor and a string of LEDS from the + of the bridge to the -. If you then consider a second (eg) section on the string (as they often do - a 50 ct string will often be 2 x 25, 100 ct as 3x33 etc), BY passing the two A/C lines to the end of the string - it will look like you should have 4 wires in each section. But this wastes copper (wire).

    So, consider SPLITTING each bridge: half of the bridge in the first blob, the other half on the second blob. The following segment uses the other HALF of the bridge in the second blob, and half the bridge in the third (last) blob. The only gotcha is the resistor: it doesn't matter WHERE it really is (but logically seems best at the "end" of the string). Let's assume the resistor comes off the + output of the bridge.

    From this, can you draw up the diagram of the string??? I'm still looking for mine.

    This is important because it is much easier to do this (to your one string segment) than it is to add another (return) string.

    Jimboha
    Springville, Utah

  5. #5
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    Default Re: Replacing rectifier or blob

    OK, I found them. Now I'm updating it with some important notes - then I'll post them here. What you will notice is that there are lots of ways that full-wave blobs can be configured, which is really only important if you're trying to cut apart the sections of a full-wave string [which I did]. The actual way used will often be the easier to manufacture OR cheapest parts OR parts count options.

    Anyway, give me a bit. Then we'll see if you can understand (in-depth!) how they work. If you can, you'll be able to see how to make yours work!

    Jimboha
    Last edited by jimboha; 12-26-2015 at 05:01 PM.
    Springville, Utah

  6. #6
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    Default Re: Replacing rectifier or blob

    Here, chew on these for a while. Do look up another description of the operation of a full-wave or bridge rectifier. These schematic pages don't quite make that clear - they just assume that you understand it. What these DO explain is how the blobs in full-wave LED strings are configured and arranged. In half wave strings, there is always one blob per segment and you can cut the sections apart
    on the two-wire boundaries between the blobs. But full wave are different (unless then have 4 wire and 2 wire parts).


    It is possible to cut apart a 3 section full-wave string: the first new string gets the male plug and the first TWO blobs; you have to terminate the APPOPRIATE 2 A/C wires or add a female. The second new string gets the original end female plug and the last two blobs - you MUST add a male at the beginning with the APPOPRIATE two A/C wires. The third new segment is missing All bridge and resistor: you have to add your own male/female plugs AND rectifier w/resistor. If you want an end A/C connection, you have to ADD a return wire. Else you can just NOT connect one of the A/C wires at the front and use it for the - connection. Look at the diagram this will become clear. In either case, you have to determine the value of the resistor: if your LEDs are sealed, it is difficult - if not remove the closest one to the blobs, look at the schematic and figure out which pair of wires will contain the resistor and measure it. It may take trial and error, or LED at other end/blob.

    Big disclaimer: You MUST understand basic electricity, read and understand the schematics, and know how to verify everything with your VOM to make sure schematic really matches your string(s). Otherwise you will likely mess up your full wave LED strings.

    Jimboha
    Last edited by jimboha; 12-26-2015 at 01:59 AM.
    Springville, Utah

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  8. #7
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    Default Re: Replacing rectifier or blob

    Jimboha, those are great schematics with a really good explanation.

    Thanks for posting them.

  9. #8
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    Default Re: Replacing rectifier or blob

    Thanks for taking the time to build and share this. I'm going to have to study up. These are by far the best diagrams I have seen.
    Just remember. Wireless is nice. Copper is king!

  10. #9
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    Default Re: Replacing rectifier or blob

    Quote Originally Posted by dvc2013 View Post
    Jimboha, those are great schematics with a really good explanation.
    Thanks. I was mainly documenting that for myself, so the explanations are somewhat sparse. But I'm glad someone else can understand what the schematics are trying to show.

    I actually thought that the trick of splitting the bridge across two blobs to reduce the wire count was rather ingenious: perplexing at first, but ingenious when you figure it out.

    Jimboha
    Last edited by jimboha; 12-26-2015 at 05:05 PM.
    Springville, Utah

  11. #10
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    Default Re: Replacing rectifier or blob

    Great schematics. I spent some time last year trying to figure this out for some CDI 100ct strings. I believe you said you had these same strings. Did you actually figure it out which of your schematics they use?
    I got reasonably close to the same schematic by probing with the DMM. I didn't go as far as you in documenting it though. I did not discover if they used a resistor in the strand. Did you determine that they in fact have a resistor in there, and in which configuration?
    After cutting one string, I kept two sections intact and working. This effectively abandoned half of one rectifier. And with the remaining section. I ended up replacing one blob with a half populated full wave converter pcb. It worked and continues to work. But I did not include a resistor. Either I got lucky and the remaining original blob had the whole resistor in there, or it's not necessary to use one.

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