Troubleshooting EPS-135 Power Supply: Low Voltage and Continuity Issues

Question:
I bought the info for the EPS-135 but am struggling to identify which defective component. I am looking for common failure points and test points, but I cannot find them anywhere. How do you know what the correct voltages should be? I am getting continuity between fuses and 120V AC input, but 1.2V out instead of the expected 42V.
 
Answer:
Thank you for contacting us, and I am sorry for the late reply. We know that printer problems can be highly annoying, and we do our best to provide the most detailed and precise troubleshooters to solve them. We at BCH Technologies would like to thank you for watching and supporting us on our YouTube channel, BCH Technologies. We use your feedback to help us improve our knowledge and our guidance to our customers.
To answer your question, there are three output pins you need to test on the EPS-135 power supply.

1. Pin (Ground): This pin is connected to the power supply's ground.
2. 42V Output Pin: This is the main output that is supposed to deliver 42V DC as long as the power supply is operational.
3. 1.2V to 1.5V Output Pin: This lower voltage output provides a secondary function and should produce a steady 1.2V to 1.5V.

Because you’re only getting 1.2V out, rather than the expected 42V, there may be a fault in the conversion circuitry of the power supply. A low 1.2V output may suggest a fault state in the power supply or a fault with the 42V regulation portion. This is a common issue where specific devices -- transistors, capacitors, diodes, etc. -- fail to keep voltage under control.
Steps to Diagnose:
 
Test the Components:

• Inspect the power supply caps. If these are bulging or leaking gas, they may need to be replaced. Capacitors also play an essential role in voltage regulation and can result in the wrong voltage output due to failure.
• Check the diodes and transistors for burn marks or cracks.
• Inspect the board for short circuits or open connections with a multimeter (especially the 42V output pin).

Verify that you have the correct input and output:

• Ensure that the 120V AC input is stable and correctly reaching the input stage of the power supply.
• Add that the output voltage across the 42V pin is not just low; it is zero. If you are getting any reading (even a low voltage), it could indicate partial failure, which aids in isolating the fault.

Fuse Continuity:

• You indicated continuity between both fuses, which means they are probably not the issue. Greysmiths first test the power supply under load, as sometimes fuses can seem intact but fail under power.

If you cannot find why based on the above steps, hopefully, the internal regulation circuitry has a more complex issue that requires a greater understanding of the electromechanics to be debugged and repaired.
Printer problems can be rather hands-on, so addressing these issues can sometimes be a rather complicated affair....we can't offer remote troubleshooting, advice, or printer repair support. We provide on-site diagnostic and repair service through our local diagnostic center (BCH Technologies Printer Repair Service).
 
Due to high demand, we are first-come, first-served. Once we have your printer there, it may take several weeks to get it serviced, but we’ll be sure to take good care of it. We have a structured way to repair either a whole printer or parts of it with us. That being said, we know that our rates are not the cheapest. So we strongly advise you to do self-help through online research. Try YouTube or our channel's home page.
If you want to search for specific videos, you can use the search icon to the right of “About” in the menu bar. I get dozens of queries every day asking for videos on specific topics. After nine years of making videos, keeping track of everyone is hard. So, it would be most effective to utilize YouTube’s search functionality. Additionally, YouTube may recommend relevant videos from other channels to help you.
Thanks again for reaching out, and best of luck with your repairs!