it seems not original hitachi have different layouts/equipment.
I have a 10 speed USB charged one.the motor with an offset weight is located inside the head assembly. I just can't find the damned silver ring holding screw)))))))) I've flexed the shaft in all directions-there's a flexible rubber/plastic cover.nothing else.it's very powerfull on ,but now doesn't work at all(worked weaker and weaker till it died completeley).maybe the battery is faulty?it worked with the USB cable attached too,without premature charging
A small fan draws air in by the head to cool the motor. Normally this is a good design, but someone forgot the air needs somewhere to go--there is no exit vent. This is probably why they slapped the 25 minute time constraint on its use.
The circuit is a pretty simple design, but they really cut corners with the motor. Sure it's big and powerful enough, but it's a cheap brushed DC motor instead of a quality AC induction motor. Since it's a DC motor, it uses a full wave bridge rectifier to convert the AC to choppy DC. The low speed is created by inserting another diode in series, effectively cutting the power in half. It's a common design.
I included a schematic as well.
I've tried opening the pic of the spring... do you happen to know the gauge, or a better gauge to replace to stock spring?
In general, the rule for oil vs. grease is to use oil on parts which have constant contact like bearings, and grease on parts with intermittent contact, like gear teeth, or the spring drive.
My Husband is an xray technician and so we have spray cans of a cleaning/lubricating agent that looks similar to wd-40 just laying around all the time. I have used it for everything from door hinges to squeaky electronics and even to kill a roach once. I knew it was safe to use on electronics but It never occurred to me to find out if it was what is BEST for them. I have no idea if it is a grease or an oil until just now I don't think I ever consciously separated the two in to subcategories of lubricant. I feel both enlightened and want to share said new found revelation with pinterest yet also embarrassingly daft for not thinking of it on my own. I guess in my head its like cooking french fries, you drop them in the oil you take them out and dump the grease the two are interchangeable. Weird. Thank you for the tip and pointing out the difference.