Intermittent no power was the complaint of this Epson lx 300 printer Repair. As usual, the main suspect was the power on/off switch. After removing the power board from the printer, I could clearly see a dry joint at the pin of the switch mode power transformer. This was the caused of the printer problem. There was no other loose connection or dry joints on the other part.
Cleaning with the thinner solution and applied fresh solder solved the intermittent no power problem. In this article, I would like you to know that not all power problems must be caused by major components burnt. A loose connections, dry joints, resistor open circuit, high esr ohms in electrolytic capacitor could cause intermittent no power or no power at all.
Troubleshooting with the right techniques and using a good procedure would normally solve electronic faults easily. Another thing that I want to share with you is that the power board is using a dual photo coupler (optoisolator) NEC PS2561-2 ic. There are two separate optoisolator ic built into one single package. If you have the ECG Philips master replacement guide book, you could find out the internal diagram of this type of ic. Once you locate the pinouts, you actually could test it with your analog multimeter. About how to test optoisolator, you could refer back to my website.
Sometimes there are more than few problems that you need to repair. In the above case, after power up the printer, it can’t print at all. It looks like there was no signal entering the CPU IC. The printer self test works perfectly okay. For your information, if this type of problems happens in other brand of printer, the troubleshooting method is the same. I will first look at the communication chip or buffer chip. In this printer, the main suspect was the Maxim Max232cwe multi channel RS232 Transceivers ic.
Solder the ic out was not a problem in this smd type ic. After the replacement with a new ic the printer works beautifully. Remember, whether you are troubleshooting the Epson lx 300 printer or any other model, first check the printer cable and then the communication or buffer