Epson L1800 Missing Ground 2 Continuity and Printhead Failure Explained

Question:
I purchased the pin chart for the Epson L1800 and have a quick question: should the pins labeled "Ground 2" have continuity to each of the blue connections, just like the ground in green? If I am missing Ground 2 completely, does this mean my printhead has failed? For context, I have three machines with related issues. Two of them blew the F1 fuse during head cleaning. After replacing the fuse and a damaged FCC cable, one unit illuminated but would not power on via the button, and later the printhead melted along with a new FCC cable. Using the provided chart, I measured 5.8 ohms on the 9-pin connector, which points to a bad printhead. The second machine was fully functional except cyan was clogged. I manually cleaned the printhead, and after powering up, it blew the transistors on the main board instead of the F1 fuse. Testing the pinout revealed Ground 2 missing, though everything else checked out. On the third machine, the main board powers up, but the printhead is clogged with white ink and also shows missing Ground 2.

Answer:

1. Ground 2 Continuity

   • On the L1800 printhead pinout, the "Ground 2" pins should indeed show continuity to the corresponding blue connections, similar to how the "Ground" pins in green function.

   • If there is no continuity on Ground 2 across multiple tests, that typically indicates an open circuit inside the printhead. Unfortunately, this condition almost always confirms a printhead failure.

2. Symptoms and Test Results

   • The melted FCC (Flat Flexible Cable) and 5.8 ohms reading at the 9-pin connector are strong signs of internal shorting within the printhead. Under normal conditions, the resistance should measure much higher; anything significantly low suggests the head is shorted.

   • The absence of Ground 2 continuity further reinforces that the internal circuitry of the head is damaged. This can also explain why the machine is blowing the F1 fuse or, in some cases, frying transistors on the main board instead.

3. Cause of Failure

   • Most often, these failures are caused by a thermal runaway event, such as when ink flow is blocked (clogged nozzles or dried channels), leading to overheating.

   • In your case, the cyan clog and later the white ink clog are consistent with heads failing under cleaning stress.

   • Once the internal ground fails, the energy has nowhere to dissipate safely, which then damages either the fuse or the MOSFET transistors that drive the head.

4. Machine-by-Machine Analysis

   • Machine 1: Replaced F1 fuse and FCC cable but head melted later. This is consistent with a head shorting internally, confirmed by your resistance measurement and missing Ground 2. Printhead is irreparable.

   • Machine 2: Cyan clog led to cleaning stress, and instead of blowing F1, the transistor drivers burned. Missing Ground 2 here also indicates the printhead is internally compromised.

   • Machine 3: Main board powers up, but head clogged with white ink and missing Ground 2. This head is also bad, and trying to run it could risk damaging the main board further.

5. Next Steps

   • If Ground 2 is missing, the printhead must be replaced. Attempting to reuse it risks burning new cables, fuses, or even your main board again.

   • Ensure that before installing a replacement printhead, you inspect and replace any damaged FCC cables, and confirm the main board transistors are intact. Otherwise, a new printhead could fail immediately.

   • For machines that blew transistors, you'll likely need board-level repair or replacement.

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