Monday, August 17, 2009


There are many times in the electronic repair industry that the technician must be inventive to overcome an obstacle. For instance, I have worked on numerous SHIMA SEIKI S-252, SFG-III I/O-C PCB's. This I/O PCB routes the Input and Output Signals to the CPU-III PCB of the SHIMA SEIKI GLOVE KNITTING MACHINE. There are three M5M8255AP-5 Programmable Peripheral Interface IC's on the circuit board. The 8255's work for the CPU-III PCB in routing the machine I/O to and from the CPU-III's data bus. As the 8255's name states, they are programmable. So when the CPU-III PCB boots up, it sends the programming information to the I/O PCB's 8255's.

So being, the only way to test the correct function of the I/O PCB as a whole unit is to program the 8255's, and then command them to perform a function that is observable. In the past, I had to unsolder the 8255's and test them individually with an IC Tester. Then I would have to test the solenoid driver transistors, and the several support IC's with the diode test function of my digital multimeter. This was a very time consuming process, for the 8255's each had 40 pins that had to be unsoldered.

With this in mind, I invented a tester that connects to the SHIMA SEIKI I/O PCB. The tester programs the SHIMA SEIKI I/O PCB's 8255's for their correct I/O function. And once the three 8255's are programmed, I am able to test the solenoid driver transistor outputs, and the basic I/O functions of the entire I/O PCB. With my tester, I am able to zero in on the exact malfunction within seconds. Whereas, it used to take an hour of unsoldering and probing with a digital multimeter to find the cause of the malfunction. The time savings for the customer are enormous. Additionally there is no doubt that the SHIMA SEIKI I/O PCB will function properly in the machine after the the repairs are accomplished.

My SHIMA SEIKI I/O PCB TESTER is based upon the PIC16F84 Microcontroller, manufactured by Microchip Technology Inc. I programmed the PIC16F84 to first program the 8255's on the I/O PCB for their correct I/O function. Then through push buttons, the PIC16F84 performs the proper SHIMA SEIKI I/O PCB Test. A group of LED's give indication of test status to the test operator.

The invention of the SHIMA SEIKI I/O PCB TESTER has saved our customers great amounts of time and money.

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