Enclosed automatic tissue processors are now a standard instrument in clinical pathology departments for handling tissue specimens. Reliable operation of this equipment ensures the integrity of the entire specimen-processing workflow and prevents inadequate dehydration from compromising the results of H&E staining, immunohistochemistry, and molecular testing. This article summarizes four fault cases involving enclosed automatic tissue processors, analyzes their causes and repair methods, and offers recommendations for routine equipment maintenance as a reference for peers in the field.
1. Working Principle of Enclosed Automatic Tissue Processors
Enclosed automatic tissue processors are based on the principle of tissue dehydration used in clinical pathology, and they use an automated control system to optimize the dehydration process. The core operating principle is chemical solvent exchange combined with automated control: by precisely controlling the immersion times for neutral formalin, graded ethanol (75%, 80%, 85%, 90%, 95%, 100%), xylene, and 65°C liquid paraffin — together with the instrument's built-in negative-pressure function, rotating platform function, and temperature-control function — the processor can apply customized dehydration protocols to different types of tissue specimens and improve dehydration efficiency. The advantage of this equipment lies in its negative-pressure system, which accelerates the penetration and exchange of chemical solvents within the tissue, while its temperature-control system regulates the temperature of the reaction chamber, speeding up the Brownian motion of the chemical solvents inside and promoting tissue penetration.
2. Fault Cases
2.1 Fault One
2.1.1 Symptoms
While the operating technician was performing the instrument's rinse and cleaning routine, the rinse program could not be started. At the same time, the main display screen showed an alarm message reading "air leak," indicating that the instrument was leaking air.
2.1.2 Fault Analysis and Repair
Since the dehydration process had completed normally just before the fault occurred, a component failure in the processor could be ruled out. The likely cause was considered to be aging of the sealing ring around the reaction chamber lid, an improperly closed lid, or debris blocking the sealing ring — any of which would reduce suction pressure in the reaction chamber and prevent the rinse program from starting. Upon opening the reaction chamber lid and inspecting the sealing ring, no signs of aging were found; however, wax deposits of varying sizes were discovered at the contact point between the reaction chamber and the lid's sealing ring. These deposits were wiped away using a wet wipe soaked in 75% ethanol, with a heat gun used to melt the more stubborn wax fragments, followed by wiping the area clean with paper towels. After restarting the instrument, the rinse function operated normally, resolving the fault.
2.1.3 Summary
This instrument relies on negative pressure to maintain the entire dehydration process, and that negative pressure continuously presses against the lid's sealing ring. If the lid is not properly closed, or if debris accumulates around the reaction chamber and sealing ring, the sustained negative pressure can cause multiple depressions and irregularities to form in the sealing ring, easily resulting in air leaks. This prevents reagent from being drawn into the reaction chamber and ultimately triggers a low-pressure alarm. In this case, the wax deposits at the contact point between the chamber and lid sealing ring were formed by drops of liquid paraffin that fell during removal of tissue wax blocks by the technician; because the paraffin had not yet solidified, it was easy to overlook. It is therefore recommended that operating technicians promptly wipe down the area around the reaction chamber to prevent liquid paraffin from solidifying and interfering with the processor's negative-pressure function.
2.2 Fault Two
2.2.1 Symptoms
Upon starting the instrument, neutral formalin (Reagent 1) could not be drawn into the reaction chamber. The instrument automatically proceeded to the aspiration sequence for neutral formalin (Reagent 2) and completed the dehydration program. After dehydration was finished, the main display screen showed an alarm indicating a reagent chamber aspiration error.
2.2.2 Fault Analysis and Repair
Because the instrument was able to automatically complete one full dehydration cycle, a failure of the negative-pressure aspiration function could be ruled out. The likely cause was considered to be insufficient liquid in the Reagent 1 chamber, or a blockage or crack in the aspiration tubing. Inspection of that reagent chamber revealed a crack in the aspiration tubing. The manufacturer's engineer was contacted to replace the tubing; after restarting and testing the instrument, the fault was resolved.
2.2.3 Summary
Because the aspiration tubing for Reagent 1 was cracked, the aspirated liquid flowed back into its original chamber, preventing Reagent 1 from entering the corresponding reaction chamber. The instrument's fully automated protective mechanism then skipped the Reagent 1 aspiration step and proceeded directly to the Reagent 2 aspiration sequence, so the dehydration process itself was unaffected — though the instrument still displayed an aspiration error alarm. Since this type of fault occurs during the dehydration program's operation, it is recommended that operating technicians routinely run the instrument's built-in engineering diagnostic program after each dehydration cycle, so that faults occurring during operation can be detected promptly and more significant losses avoided.
2.3 Fault Three
2.3.1 Symptoms
During normal operation, the reagent chamber aspiration became disorganized: the main screen showed uneven fluid levels among the intermediate graded-ethanol reagent chambers, and the program could not proceed.
2.3.2 Fault Analysis and Repair
Since the instrument was able to start normally, a fault in the tubing or negative-pressure aspiration for neutral formalin (Reagents 1 and 2) could be ruled out. Given that the disorganized aspiration involved the intermediate graded ethanol, the likely cause was considered to be a jammed internal rotary valve, preventing aspiration from one of the ethanol chambers. Manual inspection of the aspiration status of each chamber via the control panel revealed that the graded-ethanol rotary valve was jammed at Chamber 2. The manufacturer was contacted for repair; after the damaged rotary valve was replaced, the instrument's internal engineering diagnostic system confirmed that both the internal reagent aspiration volumes and rotary valve operation were normal, resolving the fault.
2.3.3 Summary
This instrument's internal rotary valve is connected to the graded-ethanol aspiration tubing and draws ethanol from each chamber into the corresponding reaction chamber in a sequence set by the system. Repeated aspiration from an intermediate ethanol chamber, combined with the rotary valve becoming stuck at one chamber and failing to rotate, prevents aspiration from proceeding to the next chamber in sequence. As a result, the instrument assumes the aspiration program for the previous chamber has not yet finished, causing the aspiration sequence to become disorganized. As with Fault Two, this type of fault occurs during the dehydration program's operation and can be managed through regular monitoring of the instrument during operation, with prompt handling of any abnormalities.
2.4 Fault Four
2.4.1 Symptoms
The main display screen went black, but the instrument remained powered on and continued running; it had already completed the full dehydration program, and the reaction chamber was immersed in liquid paraffin. However, operating status could not be observed, and the instrument could not be controlled via the main display.
2.4.2 Fault Analysis and Repair
Since the instrument continued to operate normally, faults involving negative-pressure aspiration, insufficient reagent volume in any chamber, or blocked/cracked tubing could be ruled out, leaving the internal display/mainboard as the likely cause. Opening the rear panel of the instrument revealed that the internal computer's exhaust vent was covered in dust and was not producing airflow, and the mainboard showed no heat. A vacuum cleaner was first used to remove dust from the vent, followed by wiping the vent area with 75% ethanol, with particular attention to areas around the vent that could affect the mainboard's heat dissipation. The manufacturer's engineer was subsequently contacted to service the screen and replace the internal battery and fan. After confirming the instrument was operating normally with no other faults, it was returned to clinical use.
2.4.3 Summary
The instrument's internal computer primarily controls the display interface, as well as overall operation and settings. A blackout of the screen does not interrupt the dehydration program itself, but it does prevent use of the operating interface, and is mainly caused by inadequate heat dissipation from the mainboard. In such cases, a mouse and external monitor can be connected via the USB port on the back of the instrument to review the operation log. If the dehydration program has finished, the tissue specimens can be removed; if it has not finished, the mouse can be used to terminate the program, and a backup instrument used to continue dehydration. This fault was caused by dust blocking the exhaust vent. Because the vent is located on the back of the instrument, this area is easily overlooked during cleaning. It is recommended that operating technicians periodically access the back of the processor to clear dust from the vent, preventing dust buildup from impairing mainboard cooling and causing the screen to lose power.
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