Could Not Get Replacement
Once in a while you will see some repair cases where there are no information about a particular part especially the part number of semiconductor. The other day, my repair tech asked me about a part number that i have not seen before. It started with Q followed by 4 digit numbers. The marking was a bit blur and he told me it was located in the B+ boost circuit. I told him to use IRF634 or IRF640 as replacement since this part number are quite common found in the B+ boost circuit. If it is located in the buck circuit then i will get him to use 2SJ307 or even 2SJ512/2SJ516 as replacement.
The real problem is what if you found a transistor that have weird part number and you could not find it from databook or even from the Internet? And you are not sure also the transistor belongs to what type of circuit. If you have this problem i suggest that you download a quite similar schematic diagram from another model of equipment and compare the components part number. Most of the time, manufacturers will use standard transistor code part number and you can use this guide to help you to find a near substitution.
For example, you found a part number with PR123X4 in TV color section. This part number you will definitely can’t get it from databook or from the internet. Now, download any tv schematic diagram and begin to look on the CRT section. If there is a transistor with the part number of 2SD1609 and you found that the corresponding components are quite same with the above TV then chances is high you can use 2SD1609 transistor as replacement.