How do you identify transistors easily?

Question

I'm self taught in electronics and will be starting school next month but I have so many questions. I'm working on an lcd tv and narrowed the problem down to the power supply and I'm trying to find transistors for it and am having problems. I also have a lot of problems identifying them in car audio amplifiers. Is there a site that explains how to identify the values and cross reference them? Am I getting too deep into the whole transistor thing? Is it like an electrolytic capacitor how if you stay above the voltage and capacitance you can replace them with a different value and be safe? So confused my head is boiling. If anyone can point me in the direction of a good site that explains transistors to a "T" I would appreciate it.

Answer 1

At one time it was easier to just look at a component and determine the transistor type. The descrete component package (housing) was large enough that a type was printed on it with a couple lines of printing.



for example:

2N3

906



2N3906 is a PNP general purpose transistor in a TO-92 style housing and you could use that number to look up the data sheet and find a vendor. Unfortunately with further miniturization this same transistor is available in several surface mount styles a MMBT3906 in a SOT-23 package and PZT3906 in a SOT-223 package. These smaller packages have minimal to no markings and in my experience are nearly impossible to identify without the aid of a parts list and PCB component identification. The same package styles are used for different component types as well.



Its in a SOT-23-5 package is it a



A. ) Transistor

B. ) FET

C. ) Op-Amp

D.) Any of the above



Answer D



Parts lists and component location is information that would be found in a service manual like that provided by Sams Photofacts or the manufacturer. A manual can cost $25 to $50 and up, but are worth the cost as they greatly improve your chances of make a sucessful repair.



Be aware that not all replacement components are available for retail sale or sale to the general public. I have run into a few manufacturers that refused to sell replacment parts to non certified (non authorized) repair techs. Also some components like IC's are ASIC's (Application Specific Integrated Circuit) which are custom chips that only the OEM has access to and may not sell to the general public.



Become familar with the various package styles that components come in. TO-5, TO92,SOT-23, SOT23-5 , SOIC, SOIC-W , 603 are some examples of case styles which you should become familar with.



I would highly recommend that you odered some catalogs from some supply houses and just browse through the pages. JameCo has a nice color catalog with photos of various components.



Digikey.com is an execellent online resource for parts and if they carry the part they usually provide datasheets online. THe datasheets contain a wealth of info about a part such as pin identification and function, sometimes case markings and always operational characteristics.

Answer 2

The best way to identify transistors is by the type number marked or on the circuit diagram.

If it is also marked with a manufacturer, you may find detail on their website.

Often, just putting the number into Google will turn up data.

Transistor data books are also very good.

There is one transistor marking system that vaguely describes a transistor type. This is the system that gives a number such as "2SA1986", from which one can determine the type of transistor, its makeup and the end number is its specific identifier.

Often due to space requirements with these types, it might be abbreviated. The example might just read "A1986".

When it comes to substitution there are all the variables that "Billrussel" mentions.

So you really need to find the specs. for the transistor you need to replace. Then by going through the specs. for similar transistors, you should be able to pick one that matches (or slightly betters) your dud.

Many data books have a listing of comparable types. There are also books that suggest substitutions for many common transistors.

You must be prepared to sort out different lead and outline details to suit.

Answer 3

Transistor Identification

Answer 4

This Site Might Help You.



RE:

How do you identify transistors easily?

I'm self taught in electronics and will be starting school next month but I have so many questions. I'm working on an lcd tv and narrowed the problem down to the power supply and I'm trying to find transistors for it and am having problems. I also have a lot of problems identifying them in car...

Answer 5

For the best answers, search on this site https://shorturl.im/awhoz



You can't fully check a transistor without a lot of special equipment. But the most common failure mode is a collector to emitter short, and an ohmmeter can check for that easily. Same with a LED. Don't know what a "bty" and "cct" mean. As for the leads, you need the part number and download the datasheet, as there are many different lead arrangements. However, one very common one is used for transistors mounted in a small metal can with a tab on it. Hold the transistor upside down, leads towards you. Starting at the tab, CW, the leads are E-B-C.

Answer 6

The simplest check is to use a multimeter on the resistance setting, I find the 2k range usually works best. The transistor should look like two diodes wired in series and facing in opposite directions, with the base being the junction of the diodes. In an NPN transistor the base is the anode of the diodes and in a PNP the base is the cathode. So NPN conducts base > emitter and base > collector, but not any other way. PNP conducts emitter > base and collector > base but not any other way. It's hard to tell the emitter from the collector. The way I would do it is to reverse-bias the two diode junctions. The base emitter junction on most transistors breaks down at about 5V and acts like a zener diode. You can test this with a 9V battery, a 1k resistor and a multimeter. Of course the much simpler way is to read the number on the transistor and Google it!

Answer 7

No, it's quite complicated. Transistors have lots of parameters, such as max current and voltage, current gain (at various currents), capacitance, gain-BW product, switching times, saturation voltage, power dissipation, thermal resistance.



It's a complicated decision to replace one type with a different type. You have to know the application, ie, how it is used, to see if type A can replace type B. Best is to replace it with an exact replacement, where possible.







.

Answer 8

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