Hi there,

Not sure if this is the best place to ask, but here goes...

About a year ago, I bought some LED grow lights off eBay. This is the product:

http://cgi.ebay.com.au/225-LED-GROW-LIGHT-PANEL-RED-BLUE-HYDROPONIC-15W-GSTINC-/250779379478

The other day, I noticed that about half of the LEDs had stopped working. Basically, one entire half of the board was lit up, but the other half was not. Even on that half that was a lit, several of the blue LEDs were also not lit up. The photo below shows what I mean:



I contacted the seller, and explained the problem. The seller sent me a small cicruit board (with some capacitors, etcs) and asked me to replace the existing PCB with this new one. The instructions he sent are shown below:



I replaced the PCB as instructed. When I turned on the grow lights, I had the same problem as before. Only half of the LEDs actually light up.

What is the best way for my approach this? What should I try next?

I am very new to electronics so any help would be gladly appreciated.

Thanks,
Pete

 

We need a board schematic to be of much help.

The way it went out is probably good news, but who can say without the schematic?

How much electronics background do you have? LEDs definitely fall under electronics.

You will also need some idea how LEDs work to troubleshoot it, they are not light bulbs, and have their own modes of operation and failures.

LEDs, 555s, Flashers, and Light Chasers

Please read chapters 1 and the 1st half of chapter 2, and let us know how much of it made sense to you.

We have had several projects to duplicate that panel in a complete DIY way over the years.

I just took another look at the second picture. Please tell me that is not an AC plug end? Not good if it is, really not good. If it is we probably have to start from scratch.

 

Hi Bill,

Thanks for your reply. I read the material you suggested. I understood some of it, but I guess I will have to take a step back and learn about electronics, as I don't have much knowledge there.

You are right. That is an AC power cable that you see, and the other end goes straight into the power outlet. How bad does it all appear to you?

In the meantime, I actually swapped the positions of 2 of the LEDs (one from the "good" side of the board, and the other from the "faulty" side), but that didn't result in any change - the same positions on the board were still lit up. It did show, however, the both LEDs are actually still good. Seems like the actual problem is with the board itself (or one half of it).

Anything I can try from here?

Thanks,
Petar

 

Yeah, you were lucky, that board is definitely on the unsafe side. I suspect it was poorly designed too, LEDs have working life measured in 10s of thousands of hours if used properly.

All About Circuits has an active policy about not driving LEDs directly from wall current. I don't completely agree, it could be done safely by people experienced in electronics, but the fact is the general population (such as people new to electronics and anyone around such a device) are in real danger. This gadget is worse than most, as it is not truly sealed, and poorly designed to boot.

LEDs are among the safest of parts however, a simple wall wart (power supply that plugs over a outlet) is extremely safe and with a little shopping, cheap.

Like I said, that board is too unsafe to use. I would be glad to help you build a new one using LEDs from the old one if you wish. I wouldn't try fixing the old one however, it truly presents a danger to you or anyone else around.

You are in Oz, correct? That means you have 220VAC at 50Hz for line voltage. This isn't too important, just getting it straight for myself.

If you want to build one similar to that unit you'll need a power supply such as a wall wart, 12-30VDC at 1Amp or greater. You might be able to use the existing board, I think I can talk you into using the old board, or you could use a new board such as a chunk of thin plywood drilled out in a similar fashion.

When you build one yourself you may want to build more, LEDs can also be cheap with a little shopping. The ball is in your court how you want to handle this.

If you succeed in repairing this unit it will continue to die. The fact it has done so once means a flawed design.

To test an LED in circuit is simplicity itself. You will need 3 AAA or AA batteries, battery holders are also cheap, to make 4.5VDC. You do not want more voltage, as this can blow an LED if you connect it backwards. The idea is test for good LEDs, not take out the good ones.

I'm going to draw a simple schematic, and post it here. It will be simple enough I think you can throw one together.

Other threads I've helped with (you might find some good ideas there)...

300W LED Grow Light

Need help with simple LED grow light circuit: Cash reward

Simple LED Project <very close to your setup>

 

it would appear from your PCB that your leds are wired series, in groups. This should be a relatively easy process of identifying which are out. MY suggestion would be to identify a non working group, then using a voltmeter, measure the voltage across each led. The burnt one will have the highest voltage across it.

 

It might be possible to convert the board with a dremel to 12V.
The black lines are cuts through the copper and the black dots are drill holes. It's a lot of work but maybe easier than starting from scratch.

 

It might be possible to convert the board with a dremel to 12V.
The black lines are cuts through the copper and the black dots are drill holes. It's a lot of work but maybe easier than starting from scratch.

That is more or less what I was thinking about. Odds are there is only one or two bad LEDs in the circuit, which is why I suggested the tester.

 

Try to desolder the last resistor at the place where it's not lighting and use multimeter, if the resistor is ok. The next step should be to check the LED behind this resistor.

Third thing you can try to check is: disconnect the power source, and use a multimeter buzzer to check if all GND are connected together, the same, if all input paths are connected to positive source

Tom

 

Hi again,

Thanks you all for your replies. I really appreciate it.

Recently I ordered a multimeter so that should be arriving any day. I will then try what you have suggested.

Regarding the battery test, I will try that tonight and let you know what I find.

Bill, thanks for the links to those other relevant threads.

I have a spare wall wart, as shown below. That looks OK to use (yep, I am in Australia)?

I have uploaded some photos of the main board. It's really the entire left side of the board (the entire half) that is not working. BTW, excuse the two wires (black and red, to the left) that are not attached to anything. I desoldered them to check whether that would make any difference. Soldered or not, the same exact LEDs do not light up.

Top left:

Top right:

Bottom left:

Bottom right:

Regards,
Pete

 

Like I said, you probably only have one or two bad LEDs. It is also possible their "update" isn't installed correctly, but I put that as a lower probability. Whenever you are troubleshooting it is working through the things that 'might' be wrong.

The local text book has a section on LEDs you might find helpful.

http://www.allaboutcircuits.com/vol_3/chpt_3/12.html

If you decide to go that route, the power supply you showed is fine.

 

Hi Bill,

Just an update regarding the LED grow lights...

With my new multimeter, I checked the LEDs using the diode measurement. Most of the LEDs showed nothing (multimeter displayed '1'), but for the ones that did show something, the actual values were all over the place... i.e. 40, 100, 500, and even 1,900 mV.

Also, for the some of the LEDs, I would get the exact same values even after swapping the positions of the multimeter's red and black probes (i.e. around 40 mV in some cases). Does that mean that anode and cathode could actually be connected to each other, i.e. via the solder joint?

One other thing I noticed is that even more of the LEDs do not work when I plug in the unit to test it. My grow light panel only has 1 and 1/2 rows of working LEDs now.

I would be quite prepared to build this thing from scratch, as I have a feeling that just about all of the LEDs have had it... unless I am doing something wrong with my multimeter usage.

If there is nothing else I can try in attempts to repair this thing, I would be quite happy to try and build a new one, as you suggested. Any tips on where to from here?

Thanks for all your help.

Cheers,
Pete

 

Yeah, a lot of people giving advice haven't really gone through the process. There was a reason I suggested the LED tester. A meter isn't really that good for measuring a LED and whether it is good or not. The circuit I showed will work, but the LED will glow just a little.

The expensive thing about a grow light is the LEDs themselves, and LEDs generally aren't that expensive.

Meanwhile, here is another grow light thread that popped up...

LED confusion need clarification, not asking about resistors