Direct Color Systems 1800s15 Error 71H: Epson L1800/1390/1430 APG Sensor and Timing Gear Alignment Guide

Question

I recently purchased a Direct Color Systems 1800s15 UV printer and understand that it is built around the Epson Stylus Photo 1390/1400/1430/L1800 13-inch, six-channel A3+ print engine platform.

According to the seller, the printer was rebuilt in-house with a new capping station, printhead, cables, motherboard, and other parts. The printer powers on, but it reports a carriage-related sensor error. The specific error code is 71H.

I have watched your video about APG orientation. Because the machine was recently rebuilt, I am wondering whether the mechanism that raises and lowers the printhead/carriage shaft may have been installed in the wrong position. In particular, I am not sure where the arrow or timing mark on the APG gear should be when the printhead is parked at the home position.

Could you explain what error 71H means and how the APG sensor and timing gears should be checked?

Answer

What Does Error Code 71H Mean?

On the Epson L1800/1390/1430 family of print engines, error 71H is strongly associated with the APG system. APG stands for Automatic Platen Gap. This mechanism changes the height of the carriage shaft and therefore controls the distance between the printhead and the printing surface.

During startup, the printer operates the APG mechanism and expects the APG sensors to report the correct positions. If the motor turns but the expected sensor state is not detected, or if the APG mechanism cannot reach the position expected by the controller, the machine can stop with 71H. BCH has also documented 71H as a common symptom of APG-unit problems on the L1800, 1390, and Artisan 1430 platform.

Because your machine was recently rebuilt and several major components were replaced, I would pay particular attention to mechanical APG alignment and wiring before assuming that another new part is required.

Possible causes of error 71H include:

• An APG gear that was installed one or more teeth out of phase.

• An incorrectly positioned left or right PG cam.

• A defective APG photointerrupter sensor.

• A broken, bent, missing, or incorrectly positioned sensor flag.

• An APG motor that is weak, damaged, disconnected, or unable to move the mechanism.

• A damaged, pinched, disconnected, or incorrectly routed APG sensor cable.

• A gear, carriage shaft, or cam that is mechanically binding.

• Incorrect assembly after the printer was rebuilt.

• A motherboard or wiring configuration that does not match the original APG arrangement.

• A modification made by Direct Color Systems that bypasses or electronically emulates part of the original Epson APG system.

The 71H Error Is More Specific Than a General Carriage Sensor Error

Although the seller may have described this as a "carriage sensor" problem, 71H points me more toward the platen-gap/APG system than toward the normal CR encoder system.

The CR encoder system determines the carriage's horizontal position using the encoder strip and carriage encoder sensor. The APG system, on the other hand, controls the vertical position of the carriage shaft and printhead.

The two systems interact during the printer's startup sequence, so a problem with the APG can sometimes look like a general carriage problem. The carriage may move, stop, move again, and then generate a fatal error. However, with 71H specifically, I would investigate the APG mechanism first.

Where Is the APG Sensor?

If you are standing in front of the printer, one of the areas I would inspect first is the left side of the printer around the APG mechanism.

The sensor itself is a small photointerrupter. It has a slot between two sides of the sensor. A plastic flag or tab moves into and out of that slot, allowing the controller to determine the position of the mechanism.

You can see an example of the sensor here:

APG photointerrupter sensor for Epson L1800, 1390, Artisan 1430, and related models [https://bchtechnologies.com/products/epson-photointerrupter-widely-used-as-pe-sensor-apg-automated-platen-gap-sensor-others-l1800-1390-artisan-1430-wf-3620-wf-3640-wf-4630-wf-463x-series?_pos=2&_sid=8f4c9323d&_ss=r]

There are also videos on that product page showing the sensor and related troubleshooting information. The sensor is used on the L1800, 1390, Artisan 1400/1430, and other Epson mechanisms.

Where Should the APG Timing Arrow Point When the Printhead Is Parked?

This is the important part of your question.

I would not use the parked printhead position alone as the reference for positioning one arrow on the APG gear. The factory procedure is based on phase-aligning several timing marks together, rather than simply pointing one arrow in a particular direction while the carriage is parked.

The Epson L1800 service procedure specifies two important relationships when the APG assembly is phased:

1. The delta/triangle mark on Spur Gear 16 is aligned with the corresponding delta mark on the Combination Gear 22, 28.8, 32.4.

2. With the appropriate tab visible through the notch in the PG frame, the delta mark on Spur Gear 16 is aligned with the delta mark on the left PG cam.

In other words, you are synchronizing the gears and cam to one another. You are not simply choosing an arbitrary "arrow up," "arrow down," or "arrow toward the carriage" position. Epson's L1800 service documentation specifically describes this multi-mark phase alignment.

This distinction is particularly important in your situation because the printer has apparently been disassembled and rebuilt. If someone removed the APG assembly, carriage shaft, or associated gears and then reinstalled them one or more teeth out of phase, the APG motor can physically move while the sensors report a position that does not make sense to the controller. That can lead directly to the 71H error.

Why the Parked Carriage Can Be Misleading

The APG mechanism does not remain in one fixed position throughout the complete startup process. The printer can change the platen gap during initialization and then return it to another position.

Therefore, seeing the printhead parked on the right side does not necessarily tell you by itself which tooth of an APG gear should be engaged. The important relationship is the mechanical phase between the APG gears, cams, and sensor flags.

This is why I would compare the actual timing marks rather than relying entirely on the visual position of the printhead.

Check the Sensor Flag as Well as the Sensor

A new sensor will not correct the problem if the flag that activates it is incorrectly positioned.

With the printer unplugged, examine the APG mechanism carefully and determine whether the sensor flag actually passes through the slot in the photointerrupter as the mechanism moves.

Look for:

• A broken plastic flag.

• A flag installed on the wrong side of the sensor.

• A bent or displaced mechanism that never enters the sensor.

• A gear installed out of phase so that the flag cannot reach its expected position.

• A sensor that has become unclipped or shifted from its mounting position.

• A cable that was forgotten during reassembly.

Do not force the gears or carriage shaft if they reach a hard mechanical stop. If the gear train is incorrectly phased, forcing the mechanism can damage a gear, cam, motor, or shaft.

Check the APG Motor and Wiring

Because the seller reportedly replaced the motherboard and cables, I would also pay particular attention to the wiring.

A machine can have perfectly good APG gears and sensors but still generate 71H if the sensor signal is not reaching the controller.

The stock Epson design uses an APG motor together with APG position sensors, and Epson's service information specifically calls for checking APG sensor connectors, connector cables, and the sensors themselves when an APG-related fatal error occurs.

Make sure the rebuild did not leave you with:

• A disconnected sensor plug.

• A connector placed into the wrong socket.

• A partially seated connector.

• A pinched or cut wire.

• A damaged connector pin.

• An incompatible replacement motherboard.

• A harness from a slightly different Epson variant.

A "new" motherboard or cable does not necessarily rule out the electrical side of the problem, especially after a complete rebuild.

Your DCS 1800s15 May Not Use the Stock Epson APG Configuration

This is another very important consideration.

Your Direct Color Systems 1800s15 is not a completely stock Epson L1800 or Artisan 1430. It uses an Epson-based mechanical platform, but Direct Color Systems may have modified the wiring, controller electronics, firmware, platen-gap system, or initialization sequence for UV printing.

Some converted machines eliminate, bypass, relocate, or electronically simulate part of the original APG system.

Therefore, if you inspect the printer and do not see wiring going to an APG sensor where the Epson documentation indicates one should be, do not immediately assume that somebody forgot to connect it.

It is possible that the manufacturer intentionally changed the system and that the APG signal is being handled or emulated by the conversion electronics.

If that is how your particular DCS machine was designed, the standard Epson APG arrangement may not completely apply. In that situation, you would need information from Direct Color Systems or from the person who performed the rebuild, because we would not know how their proprietary electronics or firmware expect the APG signal to behave.

What I Would Investigate First on This Particular Printer

Because the machine reportedly received a new capping station, printhead, cables, motherboard, and other components immediately before developing 71H, I would not start by buying more parts.

I would first inspect the APG assembly and determine whether it was disturbed during the rebuild.

The most important things I would want to establish are whether the APG gears are correctly phase-aligned using their factory timing marks, whether the left PG cam is correctly synchronized with Spur Gear 16, whether the sensor flags correctly enter and leave their photointerrupters, whether the APG motor can move the complete mechanism without binding, and whether all APG wiring is connected according to the configuration intended for this particular DCS machine.

If everything mechanically matches the Epson arrangement but the sensor never changes state, the APG sensor becomes a stronger suspect. If the sensor and mechanism work normally but the controller still reports 71H, then the wiring, motherboard input, or DCS-specific controller modification becomes more important.

Because this is a converted UV printer, I would be particularly cautious about changing gear positions based solely on a stock Epson photograph. First determine whether DCS retained the complete original APG mechanism or modified it.

Addressing printer problems can be complicated because many diagnoses depend on physically observing, measuring, and operating the machine. For that reason, we're not able to provide individualized remote troubleshooting, repair suggestions, or ongoing repair support. We do offer in-person evaluation and repair through our BCH Technologies printer diagnostic and repair facility [https://bchtechnologies.com/printer-repair-service]. Because demand is high, our work is handled on a first-come, first-served basis, and there may be a wait of several weeks before we can accept a printer for drop-off. Our repair options cover either complete printers or certain individual components, and the service page explains how to proceed. We also recognize that our professional repair rates may not be the most economical choice for every situation, so we strongly encourage self-help and online research whenever practical. A good starting point is YouTube or the homepage of our BCH Technologies YouTube channel [https://youtube.com/@bchtechnologies]. On our channel, use the search icon located near "About" on the right side of the menu bar and search for terms such as L1800 APG, 71H, APG sensor, APG gear, or Artisan 1430 APG. I receive dozens of questions every day asking whether we have a video on a particular subject, and after creating videos for more than nine years, it is difficult to remember every video we have published. Using YouTube's search function is usually the fastest method, and YouTube may also recommend useful videos from other repair channels.

Thank you again for contacting BCH Technologies, for subscribing to our channel, and for taking the time to describe the machine and the work that has already been performed. We sincerely appreciate your support and hope the information above gives you a clearer understanding of what error 71H is actually detecting and where to focus your research.