TECHNICAL SUPPORT
Published 2026-03-21
You got a new ultra-miniatureservo, but found that the plug doesn't fit the board you have? Or maybe it’s hard to solder the wires, but the connection is bad as soon as the power is turned on? Don't worry, this kind of problem is too common in DIY projects. Today we will specifically talk about this JST connector that gives many people a headache, how to choose it, how to connect it, and how to make it work stably.
JST is actually the name of a Japanese connector company. The "JST plug" we usually refer to refers to their various micro connectors. The most commonly used ultra-miniatureservos are SH series and GH series. The pin spacing is 1.0mm and 1.25mm respectively. They look similar, but if they can’t be plugged in, they just can’t be plugged in. ️The easiest way: take a look at what the original plug of yourservolooks like, take a photo and search online, or directly search for keywords such as "1.0mm JST SH 3P" with spacing and number of pins.
If you don't have the original plug on hand for reference, then you have to look at the current and signal requirements of the servo. The 1.0mm pitch SH series is more compact and suitable for weight-sensitive small aircraft and micro-manipulators; the 1.25mm GH series is more stable in plugging and unplugging and is not easy to loosen in a vibrating environment. Be careful not to just look at the color. The rubber shells used by different manufacturers may have the same color but different specifications. If you are not sure, buy a few commonly used specifications and try them out. Anyway, they only cost a few cents each, so the cost of trial and error is very low.
When soldering the plug of an ultra-miniature servo, the biggest fear is that the plastic shell will be damaged or the wires will be soldered in a mess. You need to prepare a pointed soldering iron. The blade is fine but easy to connect to the soldering iron. The temperature should be adjusted to about 320°C. If it is too high, the plastic will easily deform. Strip out 2-3mm of copper core from the wire, first tin the wire ends, and apply a thin layer of tin to the plug pins so that they can be soldered with just one touch without the need for prolonged heating.
During the specific operation, use tweezers to clamp the wire, place the wire end on the pin, point the soldering iron tip on it for 1 second and then remove it. When you see the solder infiltrating naturally, it is successful. Don't blow with your mouth, and don't move in a hurry. Wait three to five seconds for the solder joint to solidify naturally. Among the three wires, the red one is the positive pole, the brown or black one is the negative pole, and the remaining one is the signal wire. It is best to use a multimeter to confirm the pin definition of the servo before soldering. Many manufacturers do not follow the routine.
Poor contact is the most annoying fault. Your servo will turn for a while and won't turn, or it will shake. Most likely, the plug is not inserted in place or the pin seat is oxidized. The JST plug must make a "click" sound when it is inserted into place. If it feels loose, use pointed tweezers to gently pick the pin to allow the elastic piece in the pin seat to regain its elasticity. Don't use too much force to break it.
If the surface of the pin is black or gray, use a cotton swab dipped in alcohol to wipe it, and then insert it again after it is dry. Another situation is that the inside of the wire root is broken but the outer sheath looks fine. When you pull the wire, it comes into contact, and then breaks again. This can only be cut and redone. If you want to fundamentally solve the problem, you can cover the plug with a short piece of heat-shrinkable tubing and wrap the plug and the end of the wire together. This can both reinforce and prevent detachment, which is especially useful in projects with heavy vibrations.
There are two ways to make plugs: crimping and soldering. Crimping is to use special pliers to clamp the metal terminal to the wire, and then stuff it into the plastic case. This is what factories do. The advantage is that each wire is evenly stressed and has strong tensile strength. However, it costs one to two hundred to DIY a crimping plier, and you have to practice several times before you can press it properly. If a novice presses it, the wire will be pulled out, or the terminal will be deformed and cannot be inserted into the case.
Welding requires few tools, just a soldering iron. However, the problem is that the solder joints are hard and easy to break when bent frequently, and the plastic shell may melt and deform when the soldering iron heats up. My suggestion is: just solder one or two wires at a time, and it’s okay to be careful; if you need to use it frequently, or the project has a lot of plugs and a tight space, buy a crimping plier and learn to crimp. It will save you worry in the long run, and the wires you make can withstand the tossing.
The first misconception is that all micro plugs can be plugged into each other. Someone took a 1.25mm plug and pushed it into the 1.0mm socket. As a result, the contact surface of the pins was only a little bit. After a few days, the contact would be poor. In severe cases, the servo drive board would be burned. The second misunderstanding is to plug in directly regardless of the positive and negative poles. The ultra-miniature servo does not have a fool-proof design. If it is plugged in backwards, it may not rotate, or it may directly burn out the internal chip.
Some people leave the servo cable too long, and the cables are coiled together, which interferes with the signal and shakes the rudder. Generally, the signal line of ultra-miniature servos does not exceed 30cm, which is safer. Finally, many people like to use a lighter to burn the wire sheath to strip the wire, which causes irreversible oxidation of the copper core. The tin cannot be applied during subsequent welding. Use wire strippers or nail clippers to peel off the wire slowly. Don't be lazy.
After soldering or pressing the plug, don't rush to install the machine. Do two tests first. The first is the continuity test: use a multimeter with a buzzer setting, one end to test the metal part of the pin, and one end to test the copper core at the other end of the wire. The beeping sound indicates that the path is normal. If there is no sound, it means there is a weak solder or it is not pressed tightly. All three wires must be tested, especially the signal wire, which is most easily ignored if it is broken.
The second is a pull test: gently pull each wire to see if the solder joints or crimp points are loose. If the servo reacts when you pull but recovers when you let go, it means that the internal wire core has been broken but the outer sheath is connected and must be replaced. Finally, connect the servo tester or microcontroller, turn on the power and let the servo rotate back and forth a few times. At the same time, gently shake the wire with your hand to make sure that the servo does not shake or get stuck during the shaking process. This will be considered a pass.
Have you ever encountered the embarrassing experience of the servo suddenly "stopping" when displaying your work because the connector was not handled properly? Tell us how you solved it in the comment area, or share your experience of "rollovers" so that everyone can avoid pitfalls together.
Update Time：2026-03-21
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