During my early days in studying electronics, i was given a list of transistor code/numbering by my lecturer and when you look at any transistors part number you will be certain that the transistor would be belong to which faimly either the NPN, PNP, P-channel FET, N-channel FET, UJT, and etc. For example: A (European code) or 2SA (Japanese code) is a PNP transistor without you have to measure it with your multimeter. Since starting from mid of 90’s there are many manufacturers produced transistors part number that do not follow the standard code and this has made a hard day for electronic repair technicians to find out what type of transistor was that.
The worst case was even the internet and the latest semiconductor databook also do not have such information. Let’s take this part number J6812 as an example. If we are a seasoned electronic repairer we would have surely know that it was a HORIZONTAL OUTPUT TRANSISTOR (HOT). But what about newbiews? If they follow the standard code part number they would have thought that it was a P-channel FET. In Monitor repair there are part number that start with J306, J307, J512, J516 and etc. The newbies would have confused and the J6812 (we have also J6810, J6815 and etc) is made from Fairchild Semiconductor.
You can try search for C557C which is also a PNP transistor! From data book many people will look at S2C557 and they may have thought it was a NPN transistor. This mistake could be a trap for them and end up could not get the equipment ot work. If by following the standard code the C should be belong to NPN like the C945 (2sc945), C1815 (2sc1815), C1213 (2sc1213) and etc. Hope after reading this post you will be more careful identifying transistor part number.
source Mr.Jestine yong
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