Fixing Dented Capacitors on a RC Helicopter Receiver Board

[karabiner98k]

This video claims you can remove capacitors without soldering! But it seems more complicated!

 

[Asymptotic]

This video claims you can remove capacitors without soldering! But it seems more complicated!

It's a neat technique to remove surface mounted electrolytics, but isn't applicable in your case.

If you can get at the leads with a small diagonal cutter I'm with @dlgoff 's method in post #30. Since they won't be salvaged anyway, an alternative (but messy) method is to cut through the entire capacitor near the bottom of the can using an appropriately large pair of dykes, and nibble away at whatever remains of the bottom of the capacitor until you make it down to the leads.

If you take care, a third possibility is to bend the capacitors over (like the damaged cap indicated by the blue arrow had been) until there is enough clearance, then cut off the leads.

 

[Rive]

This video claims you can remove capacitors without soldering!

The 'you can' and the 'you should' are two entirely different concepts...

 

[karabiner98k]

Today, I found someone who told me he has a 80W Soldering Iron which is suitable for the job. What do you think?

 

[Asymptotic]

Today, I found someone who told me he has a 80W Soldering Iron which is suitable for the job. What do you think?

How many watts is the soldering iron you had tried earlier? An 80W iron produces a lot of heat, and you'll have to be careful to limit the amount of time the tip is in contact with the PC board and capacitor lead, or the solder pad will lift off from the circuit board.

Can't say what specific solder was used on this helicopter PCB, but lead-free rosin core electrical solders are usually an alloy of tin,silver, and copper (plus perhaps antimony, bismuth, and a range of other metals in trace amounts) and require from 10 to 20°C more heat than traditional 60/40 tin/lead solder. Don't know about low wattage irons (say, in the 15 to 20 watt range), but an iron of 25 watts or higher ought to melt lead-free solder just fine.

Only a small area on the tip comes into direct contact with the work piece. Hot solder on the tip's surface performs most of the thermal coupling, so once oxidation is wiped off, flow a little bit of fresh solder onto the tip.

 

[karabiner98k]

How many watts is the soldering iron you had tried earlier?

There was nothing written on its package about how many watts it produced.
Before my borther try to desolder it (which led to failure), I could bind the remote controller and helicopter together and the motors were running. But today, I noticed that I can't bind them together and it doesn't work anymore. The PCB red light flashes but can't bind with the transmitter

Is this related to a broken capacitor due to the heat of soldering iron?

 

[karabiner98k]

Today, there was no one to help me desolder and solder the new capacitors. Even my brother left home early.
I was so unhappy about my helicopter that despite having zero experience with soldering, I decided to try it!

This is what I came up with after multiples tries (each no more than 7 seconds). I tried several times but didn't hold the hot iron more than 7 seconds on the board to prevent from damaging it. (And 30 seconds in between to cool down a bit and I would try again).

This is what I came up with after 25 mintues!

I managed to desolder one of the capacitors:

Bad news is that I put a new capacitor in place (without soldering) and tested the board and it didn't work and didn't bind with transmitter

 

[anorlunda]

Despite the damages, the board works perfectly fine and there is no visible change in helicopter flight behavior. It flies without any problems.

Bad news is that I put a new capacitor in place (without soldering) and tested the board and it didn't work and didn't bind with transmitter

In some cases, the advice is "If it is not broken, don't fix it." In other cases, you fix things preemptively to prevent disasters. Which advice is best depends on the skills and circumstances. I'm sorry that it didn't work out for you.

The unfortunate circumstance for you is that in some countries simple drones are used both as weapons and as hobby toys. Export controls don't know which applies in every case.

 

[karabiner98k]

The truth is that the board didn't work even before any soldering attempt (I tested it last night and it didn't work either). So, what I have done has nothing to do with the problem. I put a new capacitor in place (I didn't solder it just put it there) and it doesn't work now.

In some cases, the advice is "If it is not broken, don't fix it."

Other members suggested I should replace the capacitors because they will fail sooner or later and if they fail, the cost of a repair after crash would be much higher.

 

[anorlunda]

The truth is that the board didn't work even before any soldering attempt

That contradicts what you said in post #1 (unless the whole board is unnecessary for flight.)

Despite the damages, the board works perfectly fine and there is no visible change in helicopter flight behavior. It flies without any problems.

Anyhow, I'm sorry it's not working for you. Good luck.

 

[karabiner98k]

That contradicts what you said in post #1 (unless the whole board is unnecessary for flight.)

No, there is no contradiction.
1 - It worked after crash (despite the damages)
2 - Some days after that it didn't work
3 - My brother tried to desolder it but failed
4 - I tried to desolder it but succeeded and removed one of the capacitors and put a new one in its place (just put it without soldering) and it doesn't work now

This is the whole story.

 

[Merlin3189]

Looking at your photos it seems you made a good job of removing the capacitor. I don't see any sign of damage to the tracks & pads, overheating nor collateral damage to other components. The only thing you might do, is to clean up any spikes of solder round the pads - probably just remelt them and they'll shrink back to the pads - particularly the positive lead.

It's a bit worrying that the binding doesn't work, as I think these capacitors are associated with the power to the motors, rather than the receiver. Look carefully to check that you haven't dropped a bit of solder on another part of the circuit and that you haven't broken or dislodged any connectors. Check that the small board with six pins connecting it to the main board is still ok and you haven't broken or dislodged any of its connecting pins.

Having got as far as you have (I think you've got the replacement capacitors), you may as well finish removing the other capacitor and solder the new capacitors in place. If it still doesn't work, you haven't incurred further cost, other than your time & effort, but you will have gained a bit more practice soldering! I can only hope that the unsoldered connection was not good enough, or the other capacitor has now failed and may be (partially?) shorting the power supply.

 

[Rive]

This is the whole story.

Should you try to repair it any further and it'll turn scrap.

My educated guess is, that it is still just some minor 'wear' problem which could be solved easily by any experienced people.

But at this point I'll take down the 'watch' from this topic.

 

[karabiner98k]

I soldered the new capacitor. Still doesn't bind.

Check that the small board with six pins connecting it to the main board is still ok and you haven't broken or dislodged any of its connecting pins.

I'm also suspicious about the small board because it is responsible for binding. How can check its pins?

 

[karabiner98k]

I gave up with this board. Even if it was possible to repair it, I would never trust it to send my helicopter up in the air with a board that seems to malfunction again at every moment.
I will try to buy a new one despite the fact that it will cost me a fortune! I have no other choice!

 

[Merlin3189]

Sorry you're still not getting success. Your suspicion of the little board sounds right. The pins themselves are fairly tough, but bending them to and fro can break tracks or bad solder joints. You are looking for mechanical damage, but it may be hairline cracks which are very difficult to see. The solder joints look ok apart from the end one, which I can't see clearly. The solder should be a smooth continuous curve from the pin to the board. There are lots of articles on the web showing good and bad joints eg.this on Adafruit which also has advice on how to avoid them.

Your soldering of the capacitor looks very iffy! (The black ring) I can't see the rest of the joint, so there may be a perfectly good one hiding underneath, but blobs like that are not good. It looks like the solder sticking to the pin, but not the pad - probably because the pad wasn't hot enough. The soldering iron needs to be in contact with the pad and the pin, so that both heat up.

Coming back to the little board, the only thing I noticed in you very clear photo, was this

which could possibly be a solder splash.

Maybe your best hope is finding an RC model flying club and someone there is likely to have a lot more experience of these things and be able to help you out. A radio amateur club is another possibility for soldering and troubleshooting skills.

 

[Tom.G]

Looking at an enlarged view (small board enlarged to 24cm, 9.5inches) of your photo, there appears to be physical board damage at the right-most pin of the small board; as if the board itself has cracked and deformed. Also the solder joint on that pin looks suspicious. Repair would be challenging.

I agree that replacement is the best bet.

Hope you are airborne again soon!
Tom

 

[karabiner98k]

The small board had been damaged and when I wanted to straighten it, it came off the main board!

I know it may be impossible to reconnect it again to the main board but I will find someone to do it.

I won't fly with this board again but I will repair it and keep it as a spare part.

 

[Dr_Zinj]

I would replace the capacitors: they're cheap enough and I have the soldering gear. The bent connector, I wouldn't worry about if the tracks are still good and the joints ok.
I don't know if you'd be able to source a replacement board and I think that's not necessary.

This is a helicopter, so probably flown in a field, well away from high risk targets - unlike drones which get flown in high risk areas. So maybe take your chances.
I also think helicopters crash less harmfully - just broken totors.

You can even repair completely snapped circuit boards fairly easily with epoxy and some stiff strips of plastic, bamboo or hardwood as bracing splints across the break; assuming there's enough clearance for them. Glue the broken edges of the board together, glue the splints (on both sides if you can), then solder the board leads together. You may need some small pieces of wire to splice the board leads back together; which will also act as reinforcement across the break. Works pretty well for boards that are obsolete and can't be bought anymore. Of course you could take it apart to have a pattern and etch a new one. Probably would not work well with a multi-layered circuit board if they have wires sandwiched inbetween the layers.

 

[hutchphd]

I have the brushed motor version of this helicopter and am good at crashing it. Two comments: 1) The small board on the soldered header is the 2.4 gigahertz radio receiver 2) In general after a crash DO NOT BEND THE COMPONENTS BACK TO MAKE IT PRETTY! You will often do much more harm!
I have found these boards very difficult to to solder (whatever they use for solder will not flow well with any flux I have ) So good luck getting airborn

 

[karabiner98k]

You can even repair completely snapped circuit boards fairly easily with epoxy and some stiff strips of plastic, bamboo or hardwood as bracing splints across the break; assuming there's enough clearance for them. Glue the broken edges of the board together, glue the splints (on both sides if you can), then solder the board leads together. You may need some small pieces of wire to splice the board leads back together; which will also act as reinforcement across the break. Works pretty well for boards that are obsolete and can't be bought anymore. Of course you could take it apart to have a pattern and etch a new one. Probably would not work well with a multi-layered circuit board if they have wires sandwiched inbetween the layers.

Seems like an interesting idea but I think it requires quite a lot of experience and expertise!

I have the brushed motor version of this helicopter and am good at crashing it.

Woooow! Really? Do you have a brushed WL V912?!
I think the best solution is to find a new PCB. But how can I get one when it is not available in my country?!

 

[Tom Kunich]

Hello everyone,

I have a RC helicopter that crashed recently and its receiver board was damaged.

Two capacitors were dented (as you can see in the picture) and the antenna base moved a bit.

I straightened the capacitors which can be seen in the second picture.

After crash:
View attachment 226067
After my adjustments:
View attachment 226068
Despite the damages, the board works perfectly fine and there is no visible change in helicopter flight behavior.
It flies without any problems.

But the question I want to ask is that:

Is it OK to continue flying with this board and those capacitors?
I'm not an electronic expert, that's why I need your help.

Thanks in advance.

Your answer is: "indeterminate". How do you propose a picture is going to demonstrate internal damage of significant levels? The effects of a failed capacitor has different results depending on what section of the circuit it is in. If you want an answer more precise give us a schematic and show on that schematic which capacitors were damaged.

 

[hutchphd]

Seems like an interesting idea but I think it requires quite a lot of experience and expertise!Woooow! Really? Do you have a brushed WL V912?!
I think the best solution is to find a new PCB. But how can I get one when it is not available in my country?!

I got it from a chinese supplier a few years ago. Unless you have a steady stream of replacement parts you will be very frustrated. Incidentally, the electrolytic (can shaped) capacitors contain liquid and most failure modes result in the disgorgement of said liquid. If they don't leak they are probably OK.

 

[Rive]

You can even repair completely snapped circuit boards

Yeah, many miracles are actually possible. I also dealt with PCBs where it was rather an artistic restoration than repair... However, when it comes to paying up for miracles - well...
For example the original problem here would be done for the basic price (for me, that's a small table of chocolate). As for bringing it back from the end result of the continuous 'repairs', that would be almost at the price of the new.

 

[karabiner98k]

For example the original problem here would be done for the basic price (for me, that's a small table of chocolate). As for bringing it back from the end result of the continuous 'repairs', that would be almost at the price of the new.

That's exactly my problem! I don't have access to a brand new PCB for my helicopter.
Maybe the only solution is to find someone who wants to travel to my country. He can buy and bring a new PCB for me.