This may seem to be a silly question but, have you checked the supply voltage?

It appears that the LEDs may be in series groups which are then connected in parallel but with a common resistor. With this type of (poor) arrangement, as the supply voltage falls, some LEDs will not light which gives the impression that they have failed.

U were right i think. I put 2 9V batteries betwein the main power source and the LEDs and all of them worked.

 

You wired in an additional 18 volts ? ? ?

OK, you have to give us good information. Going on the assumption that the supply was supposed to be 4 VDC doesn't help. AND there's an entire circuit board we didn't discus. I don't know how we're supposed to help you with out all the information.

And I'm assuming 18 VDC in the middle of the system isn't supposed to be there. Of course, how can I know for sure?! I'm a bit bothered that i spent as much time on this as I did. And a lot of us have said things that have no bearing on the problem. Broken traces, bad solder joints, burned out LED's. The whole reason why the one in the middle lights (D1) is because the resistor drops the current, not the voltage. I'm certain there's something wrong on the board (not the LED board).

 

U were right i think. I put 2 9V batteries betwein the main power source and the LEDs and all of them worked.

That's probably not a good idea.

Don't you think It would have been helpful if you'd mentioned the driver board and the SLA battery, either of which could have been damaged in the drop. Obviously, the first thing you should check is the voltage on the battery.

 

Looks like your next project is "How to repair my SMPS SLA battery charger" .....

BTW, you need to buy a cheap "Made in China" multi-meter for the job.

Allen

 

Well. I am sorry for not mentioning the driver board, because I think for sure that is the led board. But I was wrong. I saw that driver board charges the battery etc so i was thinking it is fine. Here are the pics of driver board. Bit still dont know what could be a problem.
About power supply. Lamp uses the rechargeble battery of 7.50V.

 

Well. I am sorry for not mentioning the driver board, because I think for sure that is the led board. But I was wrong. I saw that driver board charges the battery etc so i was thinking it is fine. Here are the pics of driver board. Bit still dont know what could be a problem.
About power supply. Lamp uses the rechargeble battery of 7.50V.

Well, it's nominally a 6V battery and you still haven't confirmed that you've test it.

 

I tested it and I am not sure now. Multimeter shows 4V. Even when battery is disconnected.
Main reason why I did not susspect at the battery is because I replaced it with new one recently.

 

Just thought I'd poke in and see what's going on. Seems like a 7.2 v battery is at 4 v. How do you know this battery is supposed to be 7.2 volts? And having stuffed 18 volts in the middle of the circuit I bet you blew the charging board out. And I have to agree with Blocco, that's a 6 V battery.

A little about wet cell batteries: a 6V battery has a nominal voltage of about 6.1 volts when resting, no charge, no drain. It's float charge (or full charge) should go up to 6.8 volts and no higher. Any higher and the battery cooks out the moisture. And the battery becomes an excellent paper weight.

So before you blow anything else up, first determine if you've sacked the battery. If you don't have a good DVM, go to Lowe's or Home Depot. In their electrical department they have several to choose from. I'd stay away from Harbor Freight because they have a lot of cheap stuff that doesn't last.

Test your battery voltage AND TELL US WHAT YOU FOUND. Test the battery charger leads WITH and WITHOUT the battery on there AND TELL US WHAT YOU FOUND. Lets start at where the real problem may lie. If it's as I suspect, a sacked battery then get a big capacitor, one rated at 470 µF and 50 V, or bigger. And what constitutes bigger is a 1000µF at 25 V. Make sure you don't use a cap rated for any voltage less than 25 volts. You have no idea how many volts your charging circuit is putting out. So stay on the safe side.

Attach the capacitor (pos to pos) (neg to neg), turn on the charger and read how many volts you're getting. AND TELL US WHAT YOU FOUND. It's possible the charger is shorted and pumping way too much voltage into your battery, drying it like a desert wind.

Now, before you run out and buy a new battery, we need to determine if it's good or bad. If it's good then there's no reason to buy another one. Only after we've determined whether the charger is toast or the battery is sacked can we tell you what to try next. OR like I said a long time ago - just buy new. It's probably not worth the hassle you're going through to fix this dead horse, so consider just replacing the whole thing. Seriously.

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Kind of interesting. The "driver board" I see has what appears to be a transformer (an A.C. device), printed designation of " A C In" and plently of components used to produce a regulated voltage and current to power a matrix of LEDs.

Do what you'd like with batteries, or cells, to energize the LEDs in an attempt to get them to function properly. As mentioned in another post, it'll take over 2.4 volts to get a white LED to illuminate, and if you've correctly diagrammed your circuit it'll be easy to determine to voltage, current and power actually needed to get them all to light. Your elements may not light due to either an open circuit or a short (or very overloaded) circuit. A (relatively) high impedance short somewhere can draw enough current to cause the voltage to drop below the point required for the LEDs to illuminate. Obviously an opening in the circuit will also prevent the elements from illuminating. Location of either a short or an open will produce different results. Of course we all realize this, but we're all looking at different portions of a larger "circuit" (actually, a network of interconnected elements, any of which may be damaged or inoperative).

I"m suspecting a failed (short) component on the driver board, due to a very short overload,,, but, that's just a wild guess