JPH02117859A - Checkup of thermal printer head - Google Patents

Abstract

PURPOSE:To enable chips of the following array to be checked without replacement of faulty chips even if a shift register becomes faulty by providing a checking pad for each chip of the shift register and also a test data input circuit. CONSTITUTION:A dry circuit consists of LSI chips A to C with shift registers 41 to 43. Test pads 44 to 46 are provided for each chip (between serial out(SO) terminals of the first array and serial in-(SI) terminals). If the shift register 41 for the chip A becomes partly faulty, test data is entered to the SI terminal of the shift register for the chip B from the checking pad 45 and the chip B and other chips of the following arrays are electrically checked without replacement of the faulty chip A. In addition, test data (signals of H and L levels) is entered through the checking pad 45 from a test data entry circuit consisting of a buffer 11 and a pull-up resistor R in this electrical test.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for inspecting a thermal printer head.
In particular, the present invention relates to a thermal printer head inspection method that can improve productivity and reliability.

[Prior art]

The driver circuit in a conventional thermal head.

It has a configuration as shown in FIG.

In FIG. 2, 21 is a shift register, 22 is an input buffer, 23 is an output sofa, 24 is a latch circuit, and 25
2 is a gate circuit, and 26 is a drive circuit, which are integrated into 64 bits to form one chip.

The number of bits of the thermal head is, for example, A4 size, 8 dots/mm, 1728 bits, and 27 chips of the circuit shown in FIG. 2 are serially connected.

After implementing such a circuit, when performing an electrical inspection, a predetermined pattern of data is input to the shift register 21,
This is done by printing the driver output or reading the power supply current, etc.

Further, the shift register portion of the thermal head is shown in FIG. 3, and each chip A to C is connected in series.

Therefore, if the shift registers 31 to 33 of chip A malfunction and the output (S○) is fixed at the '1' level,
No matter what kind of data was input to the subsequent chips from the input A, only data "1" was input, so it was not possible to determine whether the chips were good or bad.

In other words, if a malfunction occurs in the shift registers 31 to 33, the chips located after the defective chip will
Due to the influence of the data output of the defective chip, it becomes impossible to determine whether it is pass or fail.

Therefore, normally, it is only after replacing the defective chip and making it work properly that subsequent tests can be performed.

Furthermore, for example, in the integrated circuit for driving a thermal head described in Japanese Unexamined Patent Publication No. 61-150357, both bit-serial input signals are converted into serial-parallel signals to drive each of the plurality of printing elements of the thermal head. In an integrated circuit for driving a thermal head, which has a shift register that outputs a plurality of signals, and an output buffer circuit that transmits the output signal of the first stage of the shift register to the next stage circuit, the output buffer circuit is configured in a three-state mode. It is configured as a buffer circuit. This allows any single chip to be selected and inspected.

[Problem to be solved by the invention]

With the above conventional technology, when electrically inspecting the driver circuit in a thermal head, if a malfunction occurs in the shift register part, the defective chip is replaced and the subsequent stage inspection is performed after normal operation is achieved, resulting in extremely high productivity. The problem is that it is bad.

Furthermore, in the method in which the output buffer circuit of the shift register has three-state output, a signal line for inspection is required for each chip, leading to an increase in cost.

Furthermore, since heat is usually applied when exchanging chips, replacing each chip one by one increases the number of times the thermal head is subjected to heat, which also poses a problem in terms of reliability.

The purpose of the present invention is to provide a thermal printer head that improves productivity and reliability by improving such problems and easily inspecting subsequent chips without replacing malfunctioning chips in shift registers. The objective is to provide an inspection method for

[Means to solve the problem]

In order to achieve the above object, the thermal printer head inspection method of the present invention comprises a thermal printer head driver circuit including a shift register made up of a plurality of LSI chips, and after serially connecting and mounting the LSI chips, In a thermal printer head inspection method that inputs a predetermined pattern of data into a shift register and reads the driver output, it consists of a test pad placed for each data output of an LSI chip, a pull-up resistor, and a low output impedance buffer. , and a circuit for inputting test data to the test pad, and when the LSI chip is defective, depending on the output level of the defective chip,
A feature of this method is that the driver circuit at the stage subsequent to the defective chip is tested by inputting test data from the test pad to the LSI chip at the next stage of the defective chip via the test data input circuit.

[Effect]

In the present invention, by providing a test pad and a test data input circuit for each chip of the shift register, if a malfunction occurs in the shift register, the test data input circuit can be used without replacing the defective chip. Test data can be input to the test pad to test the next chip.

This improves the productivity of the thermal printer head compared to the conventional inspection method of replacing each chip one by one, and also improves reliability because the number of thermal cycles during chip replacement is reduced.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram of a method for inspecting a thermal printer head according to an embodiment of the present invention, and FIG. 4 is a side view of the arrangement of test pads in the method for inspecting a thermal printer head according to an embodiment of the present invention.

In FIG. 4, A-C are LSI chips 41-43 constituting a driver circuit including shift registers 41-43.
is a shift register, and 44 to 46 are test pads.

In this embodiment, each chip (previous serial output (S○
) terminal and the serial in (SI) terminal of the next stage) are provided with test pads 44 to 46.1 For example, if there is a malfunction in the shift register 41 of chip A, the test pad 45 is used to test the shift register 42 of chip B. Input test data to the SI terminal and replace the defective chip °A.
Conduct electrical inspection of the next stage (chip B) and subsequent stages.

In addition, in this electrical inspection, as shown in FIG. input.

Next, the current capacity of the pull-up resistor R and the buffer 11 will be described when the output of the chip A is at H level and L level.

Note that vof is the power supply voltage, ZH is the output impedance of chip A (H level), ZL is the output impedance of chip A (L level), vIll is the H level input voltage to chip B, and V, L are chip B ZOH is the L level input voltage to the buffer 11, ZOH is the H level high power impedance of the buffer 11, and ZOH is the L level output impedance of the buffer 11.

First, when the output of chip A is at H level, the following (1
) and (2) are possible.

(1) When inputting H level as test data In this case, the input of chip B is connected to the power supply via the parallel resistors ZH and R, so the H level is ensured.

(2) When inputting L level as test data In this case, Iol, = VDD/ZH+ is input to the buffer 11.
A current of Von/R flows in, and the output is Vl)! It is necessary to meet the following requirements. Therefore, the L level output impedance ZOL of the buffer 11 is expressed by the following equation (i).

(i) Zot, ≦V+H/ (Voo/ZH+VDD/
R)=V+H-ZHR/Voo ・ (ZH+R) Also, when the output level to the chip is L level, the following (
Cases 3) and (4) are possible.

(3) Inputting L level as test data In this case, since the input of chip B is connected to GND via chip A and the output impedance 2°L of the knockout buffer 11, the L level is ensured.

(4) When inputting H level as test data In this case, it is necessary to ensure a voltage expressed by the following equation (ii) as the output voltage.

(ii) Voo/ (1+R(ZL+ZQL) /Z
t, -Zot,) Therefore, the pull-up resistance value and the characteristics of the buffer 11 can be defined by equations (i) and (ii).

Note that the test data input circuit of this embodiment has i
Connect and use it only when the chip is f-f or a defective chip is detected.

〔Effect of the invention〕

According to the present invention, when performing an electrical inspection after mounting a driver circuit for a thermal printer head, it is possible to easily inspect subsequent chips without replacing a defective chip of a shift register.

Thereby, it is possible to reduce the number of correction steps in the assembly process and improve productivity.

Additionally, compared to the conventional method of replacing one chip at a time, the number of thermal cycles during chip replacement can be reduced, improving the reliability of the thermal printer head6.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a thermal printer head inspection method according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a conventional thermal printer head driver circuit, and FIG. 3 is a diagram of a shift register portion in a conventional driver circuit. FIG. 4 is an explanatory diagram showing connections, and is a side view of the arrangement of test pads in a method for testing a thermal printer head according to an embodiment of the present invention. 11: Buffer, 21: Shift register, 22: Input buffer, 23: Output buffer, 24: Launch circuit, 25
: gate circuit, 26: drive circuit, 31 to 33: shift register, 41 to 43: shift register, 44 to 46: test pad, A-C: LSI chip, R nibble up resistor, SI digital real in, SO digital real out, SB nistrope signal, LD: load signal, CK: clock signal. Patent owner Rico Co., Ltd.

Claims (1)

[Claims] 1. The thermal printer head driver circuit including a shift register is configured with multiple LSI chips, and after serially connecting and mounting the LSI chips, a predetermined pattern of data is input to the shift register and the driver output is read. A method for testing a thermal printer head, comprising a test pad arranged for each data output of the LSI chip, and a circuit configured from a pull-up resistor and a low output impedance buffer and inputting test data to the test pad, If the LSI chip is defective, test data is input from the test pad to the LSI chip next to the defective chip via the test data input circuit according to the output level of the defective chip. , a thermal printer head inspection method characterized by testing a driver circuit at a stage subsequent to the defective chip.