I noticed that I didn't hear the cooling sound from one strobe.
I tried disassembling it. Fortunately it is the same type as a PC's cooling fan.
I removed the fan and tried turning with the PC's power supply. It didn't turn. So, I judged that this fan was broken and tried replacing it with working fan.
About 12V is supplied and current is flowing 120mA, new fan do not work too... Why?
Does that mean that I should finish shooting as soon as it doesn't need a cooling fan? :)