Bypass Led

[Saipion]

Hi all.
I have a led light for a fish tank, over time I think it has had some condensation build up and has a bit of corrosion. The leds still work on the strip but I can't control any of it any more (Bluetooth) and the leds change colour to whatever they want when ever they want.

I've taken it all appart and it has a built in circuit on the end of the strip. I'm thinking this is the problem and was wondering if I can cut this out of the loop and just have the leds light up.

Thanks

 

[Spoon]

Hi all.
I have a led light for a fish tank, over time I think it has had some condensation build up and has a bit of corrosion. The leds still work on the strip but I can't control any of it any more (Bluetooth) and the leds change colour to whatever they want when ever they want.

I've taken it all appart and it has a built in circuit on the end of the strip. I'm thinking this is the problem and was wondering if I can cut this out of the loop and just have the leds light up.

Thanks

Welcome to the forum mate.
Can you see signs of corrosion on the circuit?
Have you tried cleaning the circuit with some Isopropyl Alcohol (IPA) and a cotton bud?
Can you post some pics up of the circuit.

 

[Saipion]

Thank you for the welcome and reply!
I'll attach a few pics. I tried to move part of it and broke the connection I could try to solder it back together with wire but it might be easier to forget about that part if it's not needed. I would say that's possible the Bluetooth controller because of the wire coming from it?

I'm just guessing though. If I can complete the circuit and at least get the leds to light up I'll be happy ?

 

[Spoon]

Well there are signs of corrosion and also a track from the CON has come away, also a couple of pads has come off, by the looks of it. Capacitor C1 looks dodgy, but its hard to check if that has shorted without testing.
Also as LEDs work on Extra Low Voltage I wouldn't want to bypass stuff without seeing what supply is connected to this board and how the LEDs are supplied.

 

[Saipion]

Well there are signs of corrosion and also a track from the CON has come away, also a couple of pads has come off, by the looks of it. Capacitor C1 looks dodgy, but its hard to check if that has shorted without testing.
Also as LEDs work on Extra Low Voltage I wouldn't want to bypass stuff without seeing what supply is connected to this board and how the LEDs are supplied.

I've added pictures of the complete light. Where would you suggest I start with trying to make it work?

 

[Spoon]

I've added pictures of the complete light. Where would you suggest I start with trying to make it work?

Clean up the board and see if you can find the tracks going to the LED's. See what components they wire to.

 

[Vortigern]

Fried fish tonight then?

 

[Saipion]

Fried fish tonight then?

Haha luckily not. It's a spare light I'm trying to get working for a new tank

 

[Saipion]

I've been trying to follow these tracks and now my eyes are going funny haha.

So i think the yellow is white led. The white is RGB led and the black is a resistor.

RGB led gets joint to the live from the 5 holes at the start of the board. 6 RGB LEDs are linked together then stop and join to the 3 tracks on the back.

The white LEDs are harder to work out. I think they are in a similar pattern to the RGB.

this is complete guess work. Let me know what you think.

 

[Spoon]

What do the 2 big resistors connect to? The 1001's


It would be good if you could find the common line to the LED's and also the signal line to them. See where they wire back to.
Usually LED's need a current limiting resistor for them to work, some have them built in.
That's what I'm presuming the resistors next to the LEDs are. Test each side of them and see if one side all link together.

 

[Lucien Nunes]

This is driven by constant voltage at 24V, so the LEDs are likely to be in series-parallel groups. Each group will contain 6-8 LEDs of one colour plus one or more resistors in series to make up 24V. The groups of like colours are then connected in parallel. Although electrically only one resistor is needed per group, to even out the heat dissipation there will often be multiple smaller resistors, each between two LEDs, making up the total required resistance value.

For each colour there will be a track running nearly the full length of the strip, which is usually the negative. At the beginning of each group there will be a tap-off from that track that then runs through the LEDs and resistors of that group and returns to the common positive track that usually serves all colours. The next LED of that colour will be the start of the next 24V group. So a cross-section at any point along the strip will usually reveal the common positive, the main negative tracks for each colour, and the local interconnections within some of the series strings. Obviously what emerges from the end should just be the main colour tracks and the common.

Each colour will be fed from the drain terminal of a transistor; that might be Q1- Q4 (see if each has the same terminal connected to the colour negatives.) Disconnect the transistors, make those tracks negative, and the one remaining track that goes along the strip, probably heavier than all the others, positive.

 

[Lucien Nunes]

What do the 2 big resistors connect to? The 1001's

With a zener diode and an electrolytic nearby, I expect they provide a shunt-stabilised supply, probably 5V or 3.3V, for the bluetooth receiver. They look like they are in parallel making up 500Ω; if the receiver uses 5V then they pass (24-5)/500 = 38mA which would be the maximum available receiver supply current, and dissipate 0.36W each which matches their size. The zener dissipates 5x0.038=190mW with no receiver load.

 

[Saipion]

This is driven by constant voltage at 24V, so the LEDs are likely to be in series-parallel groups. Each group will contain 6-8 LEDs of one colour plus one or more resistors in series to make up 24V. The groups of like colours are then connected in parallel. Although electrically only one resistor is needed per group, to even out the heat dissipation there will often be multiple smaller resistors, each between two LEDs, making up the total required resistance value.

For each colour there will be a track running nearly the full length of the strip, which is usually the negative. At the beginning of each group there will be a tap-off from that track that then runs through the LEDs and resistors of that group and returns to the common positive track that usually serves all colours. The next LED of that colour will be the start of the next 24V group. So a cross-section at any point along the strip will usually reveal the common positive, the main negative tracks for each colour, and the local interconnections within some of the series strings. Obviously what emerges from the end should just be the main colour tracks and the common.

Each colour will be fed from the drain terminal of a transistor; that might be Q1- Q4 (see if each has the same terminal connected to the colour negatives.) Disconnect the transistors, make those tracks negative, and the one remaining track that goes along the strip, probably heavier than all the others, positive.

Hi.
Thanks for the reply
I will have a look at the transistors today. Am I right in thinking I need to make a connection from collector to emitter and bypass base?

Thanks

 

[Lucien Nunes]

Probably best to get rid of the transistors as if anything is dead it will be those. They are almost certainly FETs, with source to -ve, drain to LEDs and gate to the receiver output.

 

[Saipion]

Well guys. Thank you for your help. Transistors removed and rewired. All LEDs work (appart from 1 blown blue). Before I could control the leds with Bluetooth but obviously I can no longer do that. I guess I can get an inline colour controller with a remote?

Either way the led works and that's the main thing!

Thank you