Hi,
I got an old Sharp EL-1195 calculator from eBay, together with other vintage equipments, for a cheap price. It is a simple calculator with a mini printer (see attached image - pic1.jpg).
This calculator uses a 3.6V DC power adapter and has a rechargeable battery. My purchase does not come with a DC adapter so I use a bench power supply and adjust the voltage to be exactly 3.6V instead. However, the calculator does not turn on at all upon power being applied. The LCD and the printer shows no sense of life whatsoever.
I opened it up and noticed that the rechargeable battery has leaked significantly. I removed the battery, and with the 3.6V DC power being applied, measured approximately 3.3V between the wires connecting the battery terminals. The 3.3V is approximate because it could increase or decrease slightly (3.2V to 3.4V) with small variations in the input power supply. I also identified a 47uF 10V electrolytics capacitor which has gone high in ESR (2 Ohm) and replaced with with a new 47uF 25V capacitor (see attached image - pic2.jpg)
However, with the capacitor replacement, the unit refuses to turn on. What is interesting is that the ON/OFF switch seems to have no effect on the voltage measured. The voltage measured at the battery terminal remains 3.3V regardless of whether the power switch on the calculator is ON or OFF. I also try to short the pins on the switch circuit board but the voltage remains unchanged
I try to look through the PCBs but nothing obvious. There is some corrosion at the leads of some of the resistors but upon cleaning, there is no difference in the output voltage. There are some points on the PCB traces which are marked as "+" - I measured voltages across those points with respect to the GND pin connected to the rechargeable battery. Apart from one point which measured 3.3V (this is connected to the positive terminal of the rechargeable battery), most other points measured around 0.8V (see attached images - pic3, pic4, pic5). One of the points marked as "+" shows a 0.15V 50Hz signal when measured on my oscilloscope. Interesting.
Unfortunately, my usual debugging techniques for digital circuit (identify the IC, find datasheet and measure the supply voltage or the clock) doesn't work. None of the part numbers (SC1J11 43513 for the LCD processor, SC6735U 1J for the printer processor and M5123L 1401, M5438P 812200 for the power supply board) has any useful search results on Google. I can't find any datasheet. Maybe they are in-house parts?
Any ideas how I can troubleshoot this calculator and get it back working? Can I assume that the power supply is OK since it produces 3.3V and proceed to look for other issues?
I got an old Sharp EL-1195 calculator from eBay, together with other vintage equipments, for a cheap price. It is a simple calculator with a mini printer (see attached image - pic1.jpg).
This calculator uses a 3.6V DC power adapter and has a rechargeable battery. My purchase does not come with a DC adapter so I use a bench power supply and adjust the voltage to be exactly 3.6V instead. However, the calculator does not turn on at all upon power being applied. The LCD and the printer shows no sense of life whatsoever.
I opened it up and noticed that the rechargeable battery has leaked significantly. I removed the battery, and with the 3.6V DC power being applied, measured approximately 3.3V between the wires connecting the battery terminals. The 3.3V is approximate because it could increase or decrease slightly (3.2V to 3.4V) with small variations in the input power supply. I also identified a 47uF 10V electrolytics capacitor which has gone high in ESR (2 Ohm) and replaced with with a new 47uF 25V capacitor (see attached image - pic2.jpg)
However, with the capacitor replacement, the unit refuses to turn on. What is interesting is that the ON/OFF switch seems to have no effect on the voltage measured. The voltage measured at the battery terminal remains 3.3V regardless of whether the power switch on the calculator is ON or OFF. I also try to short the pins on the switch circuit board but the voltage remains unchanged
I try to look through the PCBs but nothing obvious. There is some corrosion at the leads of some of the resistors but upon cleaning, there is no difference in the output voltage. There are some points on the PCB traces which are marked as "+" - I measured voltages across those points with respect to the GND pin connected to the rechargeable battery. Apart from one point which measured 3.3V (this is connected to the positive terminal of the rechargeable battery), most other points measured around 0.8V (see attached images - pic3, pic4, pic5). One of the points marked as "+" shows a 0.15V 50Hz signal when measured on my oscilloscope. Interesting.
Unfortunately, my usual debugging techniques for digital circuit (identify the IC, find datasheet and measure the supply voltage or the clock) doesn't work. None of the part numbers (SC1J11 43513 for the LCD processor, SC6735U 1J for the printer processor and M5123L 1401, M5438P 812200 for the power supply board) has any useful search results on Google. I can't find any datasheet. Maybe they are in-house parts?
Any ideas how I can troubleshoot this calculator and get it back working? Can I assume that the power supply is OK since it produces 3.3V and proceed to look for other issues?
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