Rotor Board Resistor

[superman]

So i could use some help. I am pretty sure i have the resistor going out on my rotor board. I have talked to a few people and they seem to think this is what the problem is as they get really hot on the board and burn up. I would like to go ahead and order some to replace some on my other boards. Can someone point me in the right direction? aside from being able to solder I am electronically a noob.

It seems to be a common problem and people just seem to keep replacing boards instead of the resistor, well i am at the point where i need to replace 4 and i know of a few other locals that could use the same.
Thanks.

[BrickHaus]

Should be able to find it here. I assume its a 200 ohm resistor?

[superman]

I think it is actually a 20 ohm resistor. Apparently the 200 is a code not the resistance. I was hoping someone significantly smarter than i could point to it and say try this specific one.

[Grendel]

Yup that is a 20 ohm resistor (a 200 ohm would be marked 201) and I can help you out. Put some calipers on the width and length of the resistor so I can be sure of the physical size so I can get you the correct part number to order. You comfortable in performing the soldering? If not I can re-work them, I need to come down and pick up my Sterling anyway I've been a slacker this summer.

How sure are you this is the issue? Resistors usually only fail due to improper soldering, being under-rated or as a result of excess current caused by something else.

[superman]

Id say i am more comfortable with wires than surface mount stuff, but willing to give it a shot and if i fall on my face happy to send them up.
I am pretty sure, with the board outside of the housing and turned on the resistor is very hot. i also saw posts about it awhile back but i can't seem to find those anymore (likely not on here). My understanding is that the resistor overheats and causes the issues i have where the motor is slow to start or does not start at all when stopped. I think this also causes the led to turn off for the button.

Planning to make it to fulda or the 1 day scenario in rockhill? we can meet up then if that is easier.

[Grendel]

Both the Fulda and Rockhill are on my list. Been helping daughter with renovating house so all my "free time" has not been free.

I have a rotor (version 1) around here some where I'll see about profiling the circuit with typical current draws and see if this resistor is spec-ed correctly for real world use. If the resistor is heating up and limiting motor speed that means there is more current draw then appropriate for the design. It could be as simple as upping the wattage of the resistor. Anyone have a schematic for the Rotor that would make things simpler but not absolutely necessary.

Get me the resistor dimensions in case I can not find my Rotor so I can get you some spare resistors and we can figure out getting them reworked for you.

An easy trouble shooting step is to just take a solder Iron and heat up one of the joints at a time, reflow the solder and add a little more. The picture looks like the resistor does not have good wetting to the pads. That could be poor workmanship causing the heating (increased resistance) or is a result of excess current melting the solder. If reflowing fixes it the problem is most likely workmanship at the factory.

[superman]

awesome.

I will pull it out when i get home tonight and take some measurements. I will also snap some videos to forward showing the issues. After that i will try the reflowing the solder.

[Shaftski]

All the symptoms you described scream cold solder joint. Pic confirms it for me.

Looked at the 20 ohm on my board and it's clean as a whistle. Other resistors/solder joints are visibly different than that 20 ohm junction though, that one almost looks done by hand. Just like yours. But in my case they didn't screw it up. It's aligned perfectly.

On mine there is a small bead of solder on each end of the resistor, but it doesn't flow clean out to the edges of the solder pads. I may have just been lucky that it's good enough to get by and not cause problems. More heat was needed on the pad when the resistor was soldered in originally IMO.

[superman]

yours does look cleaner than mine. hmmm

[Shaftski]

Package size on the resistor looks like 1812 (.18"x.13").

[superman]

so checked the board with the issue. turned it on and the resistor gets hotter than the sun. Did some digging found another board i had kicking around. looked at the resistor on that board and it looks clean and does not get hot. seems to be responsive as well.

tried to resolder the resistor and i think it got a bit hot and basically fell off the board. so that isn't good.

[Tarsun2]

surface mount components are a PITA.
not hot enough and it dosent do anything.
too hot will work but, too hot and too long could burn up the resistor, burn up a lower level run, or even cause the solder pad to come off/slide off.

it is hyper important to keep the solder tip clean. water and a sponge is handy for prolonged use but you could also use a blade and scrape the tip clean right before you use it. it should melt the solder as soo as the tip touches it. you shouldnt have to hold the tip on the solder for long and you should never have to roll the tip around the solder.

sometimes boards have a coating on them that you need to clean off first.

as i was always told; "practice safe soldering, keep your tip clean."

a cheap multi meter will confirm if the resistor is bad or not as well.

[Grendel]

Funny thing is I love to solder and don't get to do it much anymore. Then again I used to teach Micro/Miniature soldering in my Navy days and worked doing electronic failure analysis for years. With the right tools and practice not too bad.

[Tarsun2]

oh snap, well ok then lol

[Roger7pball]

Not sure if this will help any of you…had the typical slow spin and no LED action on a rotor I got used. Went down the rabbit hole of re-flowing that resistor’s solder after seeing this thread. Also tried a standard 20 ohm resistor in its place. Tried a different motor and even a different board. Ended up being the JST connector from the battery pack was wired backwards.

I feel not-so-smart by not looking at the direction of rotation. Oh well simple fix, live and learn haha. Maybe someone else with this rotor issue has the same problem?