Han Rong

The hardware of different models of circuit maintenance tester will be different-circuit scale, main technical indicators and so on. If you don't understand how these differences affect the test function, you will be confused when choosing the model. This paper only discusses the influence of various hardware components of the circuit maintenance tester on the main test functions, which can be used as a reference for selection to some extent.

1. Analog channel

A. number of analog channels

When testing ASA(VI) curves, the analog channel is responsible for sending analog test signals to different pins of the device, thus supporting the use of test clips and test adapters to test hundreds of curves in a few seconds and dozens of seconds, greatly improving the test efficiency. There is no tester with analog channel, so we can only use the probe to test one foot at a time. ?

Analog channels are mainly used in the following situations:

On-line test of ASA curve of IC pin (on circuit board). On-line testing requires the use of test clips to connect test channels and equipment pins. Mainly due to the lack of suitable test clips, 40 channels are enough;

Off-line test of ASA curve of IC pin (off-circuit board) (some people call it difficult device test). The number of channels should not be less than the maximum number of device pins;

The ASA curve of the interface device on the circuit board can be quickly tested through the connector outside the circuit board. Preferably, the number of channels is greater than the number of circuit board insertion pins.

B. Analog channel properties

At present, there are two kinds of testing instruments for circuit maintenance: single attribute and double attribute. When dual attribute channels are required:

"Multi-port" test method supporting ASA curve. Also known as "matrix", "cross pin" and "transfer reference point" test methods;

Support "dynamic reference" in ASA curve test (sink energy proprietary technology. Invention patent is pending);

Support "software setting reference foot".

Support IC "suspected fault degree" technology (invention patent is pending).

C. analog channel voltage range

When testing the ASA curve of IC pins, the amplitude is usually between greater than the actual working voltage and less than the maximum rated voltage, so the maximum 15V can meet most requirements.

When testing analog IC functions and digital/analog IC parameters, a wider voltage range may be needed.

2. Analog signal generation

A. signal amplitude and voltage classification

When testing ASA curve, the amplitude and voltage classification can meet the requirements of testing 3V, 5V and 12V voltage series devices. "Huineng" circuit online maintenance tester has 256 files to meet the requirements of integrated circuit parameter test and RCL online test.

B. Analog signal frequency

When testing ASA curve, the circuit board is not powered on. In the absence of power supply, IC is a series-parallel connection of a bunch of PN junctions, so the circuit nodes only consist of PN junctions, resistors, capacitors and inductors. What is the VI relation of PN junction? , regardless of frequency; Capacitance and inductance are related to frequency. The application shows that the frequency range from 1Hz to several hundred Hz can meet the requirements of ASA curve testing. The most commonly used frequency is several tens to one hundred and two hundred hertz.

Other types of tests may require higher frequency. However, the low-frequency testing tools used in the circuit maintenance tester, such as multimeter probes and ordinary flat cables, limit its support for higher testing frequencies (such as megahertz). ?

Please click to enter a picture description.

Please click to enter a picture description.

3. Precision DC parameter test circuit

DC parameter test has a good detection effect on disassembled parts and parallel imports that are often encountered in maintenance. This circuit is specially used to support DC parameter testing of integrated circuits. At present, only the tester included in Huineng's circuit maintenance test system Ver6.0 (3.0 before upgrade) series has this part of hardware.

The precise DC test unit of Huineng circuit maintenance tester can process millivolt voltage and microampere current, which are applied to the pins of the device under test through analog channels to realize parameter testing. ?

This part of hardware is not needed for ASA(VI) curve test, but ASA curve cannot detect equipment parameters. In fact, it is not difficult to understand that equipment parameters only exist when power is on, and ASA test is not powered on, so it is impossible to test things that do not exist. For example, the load capacity of the device only passed the ASA test, and the shape of the PN junction characteristic curve of the output transistor could not be seen. Only when the equipment is powered on can it really drive the load. We will discuss this problem in a special article.

4. Digital channel

The digital channel is mainly used to support the functional test of digital devices, and only deals with high and low levels (corresponding to logic 1 and logic 0), generally high impedance state.

A. digital channel voltage range

In the actual test, 0 and 1 in the test code are converted into specific voltage values. This voltage value is related to the working voltage of digital equipment. For 5V TTL series, 0 is defined as a voltage greater than 0V and less than 0.8V; 1 is defined as a voltage greater than 2.4V and less than 5V. Similarly, there are 5CMOS series, 12V series, 3V series and EIA (12V) series, all of which have their own corresponding signal voltage standards.

1)5V channel?

The high and low voltage ranges of channel output and input meet 5TTL and 5CMOS standards. For example, HN 1600 series of Hui Neng tester and most other circuit maintenance testers on the market; ?

2) All-level channels?

Refers to the channel high and low voltage range can be set, which can support the test of various voltage series standards. For example, HN2600 series of Hui Neng Tester, the level range can be set to meet the standards of testing 3.3V series to 12V series; ?

3) Combined channels?

Because the full-scale channel is complex and the grading channel is relatively simple, some testers assemble various grading channels and switch them. Although this increases the hardware scale, the design is relatively simple. For example, 40 5V channels and 40 12V channels can be combined to test 5V and 12V devices with up to 40 pins. ?

B. Number of digital channels

At present, Huineng circuit maintenance tester has 40 channels. There used to be 80 channels, but now they have stopped broadcasting. What is the reason? The following discussion also answers this question. ?

To realize the function test of digital equipment, three conditions are needed:

The number of channels is not less than the number of pins of the device under test;

The function of that device must be known.

The function of the equipment must be (effectively) describable.

There are many kinds of digital devices, mainly limited to Condition 2 and Condition 3, which are only successfully applied to logic devices (such as 74 and 4000 series). Few logic devices (74 series) have more than 40 pins. However, with the development of integrated circuits, the proportion of logic devices on the circuit board is not large, and the models with more than 40 pins are rare, which basically does not need to be considered.

Another function called "LSI device test function" also uses digital channels. This function was first realized by Huineng Circuit Maintenance Tester in 1990s. It mainly tests Z80, 6502, 8255 and other CPUs and related peripherals (very popular in 1970s and 1980s, most of them are packaged within 40 pins, but there are more than 40 pins). Mainly limited to condition 3, the effect is not good enough. With the gradual elimination of equipment such as Z80, this test function has been abandoned in the latest test system.

The above is the consideration of setting 40 digital channels for the circuit maintenance tester of Huineng circuit. However, some people still think that more digital channels should be set up and some devices with more than 40 pins should be listed. If you look closely, it is still those early, rare logic devices and LSI devices that have long since withdrawn from application. This shows that the test has not developed much, and it still stays at the level of that year. Today, it lacks practical value and basically needs no consideration. ?

There are two ways to calculate the total number of channels in the combined channel structure. For example, 20 12V channels (called high voltage channels) and 40 5V channels. Because the maximum size of measurable equipment is still 40, the total number is still 40 channels; A total of 60 channels makes sense. It's just that the calculation focus is different. From the point of supporting test function, it is worse than 40 full-stage channels.

C. digital channel frequency

This is a question that needs no further explanation, but it is necessary to clarify it now.

When testing the function of the device, the testing frequency has nothing to do with the working frequency of the device. This technical view has been challenged in recent years: some people assert that the functional test with a test frequency of 2000K(2 megabytes) is "enough to cover high-frequency dynamic parameter faults".

It is out of the question.

If the frequency of 2 MHz is enough to cover high-frequency dynamic faults, then the tester above 2 MHz is worthless. However, the American Schlumberger's 20 megabit and the British diagnosed 10 megabit are still at the top of the market. ?

The lowest frequency range of digital equipment is from 0 to tens of megabytes, and only 2 megabytes is a few tenths. How to detect the high frequency fault of equipment? For example, if a car has a top speed of 200 kilometers per hour and travels at a speed of 2 kilometers or 20 kilometers per hour, it is impossible to find performance problems related to the top speed; Similarly, when the test frequency is 2 megabytes, the high-frequency dynamic parameter fault of the device with the highest working frequency of tens of megabytes can not be detected. ?

The challenge is to give this kind of experiment to prove itself: when testing a device, the test frequency of 0.5 MHz is normal, 1 MHz is normal, and 1.5 MHz is invalid, so it is concluded that only increasing the test frequency will lead to the failure of the test, so the high-frequency dynamic parameters of the test device are invalid.

Note that the maximum operating frequency of the device shown is higher than 40 MHz. Take the car as an example. A car with a speed of 200 kilometers per hour can run at a speed of 10 kilometers, but not at a speed of 20 kilometers. In this case, it may be a road problem, a flat tire, etc. And it can't be the problem of the highest speed. By analogy, tens of megabytes of equipment can't pass the tests of 1.5 trillion and 2 trillion, and the problem should be the testers. That's true. The distribution parameters of the test channel are large, which constitutes the load of the equipment under test. This load will increase with the increase of test frequency, and eventually the test will fail due to the insufficient load capacity of the device regardless of the highest working frequency. ?

Since frequency has nothing to do with device function test, why is there a parameter of digital test frequency?

On-line functional testing of digital devices must use "post-drive" isolation technology, which limits the testing time to 26 milliseconds. If the test frequency is 1K, at most 26 tests can be conducted in 26 milliseconds; 10K can be tested 260 times. The higher the test frequency, the more test codes can be executed and the more complex the devices can be tested. As far as logic devices are concerned, the test frequency of tens of K can meet the needs of functional testing.

5. Output power supply

This part occupies a large volume on the tester, but the cost is the lowest. It is only responsible for providing working power for the tested circuit board and devices. Mainly to provide convenience at work. An external power supply can also be used. ?

At present, most domestic online circuit maintenance testers use outsourced ordinary switching power supply, and the quality is close. The difference lies in the type of power supply and current.