I have a circuit board I am playing around with trying to repair. It is from a gate operator system. The customer says the whole system took a lightning strike. I have him up and going now, but I held on to this receiver to play with.
This board is a receiver that receives a radio signal from a keypad. I am unsure of the radio frequency it receives. I do know it can be powered using 12-30 volts AC or 10.5-30 volts DC.
Onsite I determined that it would not power up, so I replaced it. The new one works.
Anyway, fast forward to now. I am looking at it to see if I can repair it. Upon closer inspection, I see 2 capacitors are blown in two. They are C18 and C28. Without having a schematic or oscilloscope or other high dollar pieces of electronic equipment (I do have multimeters), is there a way that I can determine what the value of the capacitors should be? And what type of capacitors they are? I am new in this electronics world. This is a learning project for me.
Here is the front of the board, showing the two capacitors.
If lightning caused that much visible damage I'd be concerned that other components would have damage too, especially the semiconductors.
Some capacitors are used in a way that a range is acceptable, some in a way where bigger is better and some in ways that depend on them being close to a specific value. We can only make educated guesses based on seeing a schematic.
It looks like there are many other similar capacitors on that board. If your multimeter has a range to measure capacitance you might try to measure those to see if there's a common value. You might even be able to read the value printed on them if they're positioned right.
Since you found a replacement board you may be able to find the schematic online somewhere too.
Capacitors typically are the last items to blow up, after everything else already has been damaged silently. Provided that the caps are part of the power supply you should find the supply IC and then its Application Notes with all circuit details.
The caps were likely the same as all the other small brown caps on the board.
Educated guess: ceramic multilayer 100n/50volt.
The caps seem to be in the power supply area.
I agree with @JoeHuber. Assume that all semiconductors (chips. transistors, diodes) are also toast.
Leo..
I see other similar size/type of capacitors on the boards. C3, C4, C7, probably others. Find similar type and values and see if any of them work. Boards are cheaper to build when the same values are used in different places on the board.
I was worried about this. I was thinking to fix what I could and see what happens. Then track down the next problem if possible.
Darn it. I don't like the way that sounds.
I wish I had thought of that earlier. I wasn't planning on trying to repair this one. I found it in a box while cleaning up and thought I would play with it. I have already installed the new one at a customer's house. I don't really have access to it anymore. It is a brand I do not mess with much so I don't have another one just laying on the shelf. I did have to take the cover off to program the keypad to the new one. I remember noticing right off the bat that the button, LED, and a few other things were located in a different spot on the new one. But it did look like very similar components, just rearranged some.
Thanks for the info. But...
It looks like it is not worth pursuing.
Yeah I though about measuring some others just to see what I came up with. But I wasn't sure if they needed to be exact or just "close enough to work."
I don't think I will waste my time with it. The general consensus is that even if I get the right capacitors, chances are it still won't work. I don't want to replace every component, only to find out it still doesn't work because the chip with the programming on it is fried also.
Maybe I can salvage a few things. The relay, switch, led, and few smaller components if they test good.
It's often worth replacing a capacitor that died of old age. But lightning damage especially when severe enough to destroy capacitors usually means it's not gonna work out well.
There's some small chance that the capacitors were at just the right place in the circuit to start to absorb the energy but once they exploded any remaining energy would have been absorbed by anything else connected. And since two caps exploded it shows there was enough energy for the ripple effect to occur.
I agree. I certainly was not wanting to put it back into service for that very reason. I was just wanting to tinker with it and learn more about this electronics hobby.
You can be reasonably certain that the semiconductors are damaged and will eventually fail if they were exposed to lightning. The only unknown is when; tomorrow, next week, or even next year. Without more information, it's impossible to estimate the timing of the failure.
