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Finding replacement semiconductors.

Apr 1, 1996 12:00 PM, Huseman, John M.

Using semiconductor cross-reference manuals to find replacement devices can aid troubleshooting, reduce downtime, and save money.

Modern facilities are adding the repair of solid-state devices to their list of electrical maintenance responsibilities. Knowing about the cross-referencing process will enable you to purchase replacement devices locally, instead of buying original parts from the original equipment manufacturer (OEM). This will help keep downtime to a minimum and will usually reduce the cost of the replacement parts.

Semiconductors, such as diode rectifiers, transistors, silicon-controlled rectifiers, and integrated circuits, are used in all types of manufacturing equipment and in all phases of power control. Thus, you not only must know how to test these devices as part of your troubleshooting responsibility but, in many instances, you also must select replacements for failed devices. In other cases, you may need to know the electrical specifications for a particular diode or integrated circuit. Whatever the situation, being able to cross reference semiconductor devices is a challenge you must master.

Replacement information usually can be found in cross-reference manuals. Generally, these manuals are not expensive and can provide you with a large amount of information. Besides using these manuals to find replacement devices, they also can be used to find electrical data such as the power dissipation or peak-surge current of a device. Many manuals additionally contain circuit examples of how various devices can be used in actual circuit applications.

Mechanical information is also contained in these cross-reference manuals. As with any type of electrical device (such as circuit breakers, starters, etc.), there's a certain amount of mechanical data that has to be followed for proper installation. The same applies to solid-state devices. Component failure in many cases can be traced to improper installation procedures. For instance, torque is just as important to a stud-type rectifier diode as it is to the cable lugs of a circuit breaker.

A cross-reference manual contains a minimum amount of information about the devices. For more specific design-type information, you'll have to refer to handbooks and electrical/electronic textbooks. These publications give much more detailed information about the characteristics of various types of semiconductors and the method to determine their performance in a circuit. However, most of the problems you'll encounter can be solved with cross-reference manuals. These include finding replacement devices, installation instructions, and lead and pin identification.

Selecting replacement semiconductors

To find a suitable replacement semiconductor device, you must determine what the original device number is so that it can be cross referenced. Solid-state devices can have several different numbers on them, and they all have a different meaning.

A number such as "8439" or "7940" refers to the date the device was manufactured. For example, "8439" stands for 1984, 39th week of the year; "7940" stands for 1979, 40th week of the year.

Numbers and combined letters and numbers such as "057," "212," "63B," and "6RS" are part-number prefixes that identify the manufacturer of a device. To determine the manufacturer from this information, you turn to the part-identification section of the cross-reference manual. Knowing who manufactures a device is not significant in selecting a replacement; therefore, not all manuals have a part-identification section.

Device numbers can be as simple as "IN34" or as complex as "HCC4096BE." When trying to find a replacement for such semiconductors, it's a good idea to have several cross-reference manuals on hand. A device that can't be found in one manual may be found in another.

A typical example illustrates how the manuals should be used. Fig. 1 (on page 24) shows a schematic diagram of a power supply for an electric brake. The diode rectifier has failed, and a replacement device must be installed.

The number of the original diode rectifier is "GEA40B." The first step is to refer to the directory of the replacement manuals to see if a device can be found that will work as a suitable replacement.

Referring to the cross-reference directory of the RCA-SK series manual (Fig. 2, on page 24), the SK350l device is listed as the equivalent to GEA40B.

A brief description of the SK3501 can be found by turning to the semiconductor index section of the manual (Fig. 3, on page 26). It says that the device is a silicon stud-rectifier diode with a voltage rating of 600V, has a current capacity of 40A, and is in a DO-5 case. The description also refers to page 5-3 of the rectifier section of the manual [ILLUSTRATION FOR FIGURE 4 OMITTED], where additional electrical and mechanical specifications can be found.

You can use this procedure with a cross-reference manual for any type of semiconducting device, including small- and large-scale integrated circuits. As shown in Fig. 5, the manuals are an excellent source of information for pin identification. This is especially useful as an aid in the troubleshooting process. With practice, you can become very familiar with the cross-referencing process and expand your area of responsibility to include solid-state devices.

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© 2012 Penton Business Media, Inc.

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