Printer types, and how each one actually puts ink on paper

Why this matters

Printers are the most-disliked topic in this exam and the one with the clearest payoff, because the laser printing process is a named sequence and faults are named by the stage they occur in. Once the stages are known, a print quality symptom stops being a mystery and becomes a pointer at one specific component.

That is unusual. Most diagnosis in this course narrows possibilities; printer diagnosis frequently identifies the part outright. A vertical line down every page is a drum or a cleaning fault, not a guess between four things.

The exam asks for the laser process in order, and it asks which printer suits a stated requirement. Both are decidable, and lesson 39 turns this model into a fault-finding method.

The lesson

Laser printing end to end, by stage, because the stages are how faults are named

Seven stages, in order. Learn them as a sequence and the faults follow.

1. Processing. The printer receives the page and builds a raster image of it in memory. Insufficient memory for a complex page produces a partial page or a memory error.
2. Charging. A uniform negative charge is applied across the photosensitive drum by the primary charge roller.
3. Exposing. A laser scans the drum, discharging the areas that will carry toner. This creates an invisible electrostatic image.
4. Developing. Toner, charged so it is attracted to the discharged areas, is drawn from the developer roller onto the drum. The image is now visible in toner on the drum.
5. Transferring. The paper is given an opposite charge by the transfer roller or belt, and the toner moves from the drum to the paper. At this point the toner is only sitting on the surface.
6. Fusing. Heat and pressure from the fuser melt the toner into the paper fibres. This is what makes the print permanent, and the fuser is the hottest component in the machine.
7. Cleaning. Residual toner is scraped from the drum and the drum's charge is neutralised, ready for the next page.

The faults, mapped to stages:

• Toner rubs off the page. Fusing. The fuser is not reaching temperature, or the wrong media type is selected.
• Repeating marks at a fixed interval down the page. A defect on a roller, and the interval identifies which — a drum's circumference differs from a fuser roller's.
• A vertical white streak. Toner is not reaching the drum in that column — often an obstruction or a depleted cartridge.
• A vertical black line. A scratched drum or failed cleaning.
• A completely blank page. Exposure or developing — or the sealing tape was never removed from a new cartridge.
• A completely black page. Charging has failed, so the whole drum accepts toner.
• Ghosting: a faint repeat of the previous image. Cleaning, or a drum at end of life.

The fuser is hot enough to burn. Let a printer cool before reaching into it, and never use a household vacuum on toner — the fine particles pass through ordinary filters and can produce a dust explosion hazard in the motor. A toner-rated vacuum, or a damp cloth on cold surfaces, is the correct method.

Inkjet: heads, cartridges, and why an idle inkjet fails more than a busy one

An inkjet sprays droplets of liquid ink through microscopic nozzles, using either heat to form a bubble or a piezoelectric element to flex.

The components: the print head (integrated with the cartridge on some designs, permanent on others), the cartridges or tanks, the carriage and its belt, the feed mechanism, and the duplexing assembly where fitted.

The characteristic failure is drying. Ink in an unused nozzle dries and blocks it, which is why an inkjet used once a month fails more than one used daily. Symptoms are missing colours, banding, and a gap in a specific colour channel. The fix is the printer's own head cleaning cycle — which consumes ink, so running it repeatedly is expensive and a soak or manual clean is better for a badly blocked head.

Also examinable:

• Calibration and alignment correct a carriage that is not placing droplets where it thinks, producing wavy or doubled text.
• Print quality depends on media: photo paper and plain paper need different settings, and printing photo settings onto plain paper produces smearing because the paper cannot absorb that much ink.
• Inkjets are cheap to buy and expensive to run. That trade is the answer when a scenario asks for high-volume text printing — the answer is a laser.

Thermal and impact printers, and the jobs that still require them

Thermal printers apply heat to specially coated paper, which darkens. No ink, no toner, very few moving parts. Receipt printers, shipping labels, some medical equipment.

• Consumables are the paper itself and, on direct-thermal designs, nothing else.
• Thermal transfer is the variant that melts a ribbon onto ordinary material, used for durable labels.
• Maintenance is cleaning the print head and removing debris.
• The examinable weakness: direct thermal prints fade with heat, light and time, which is why a receipt kept in a car becomes blank.

Impact printers strike a ribbon against paper. Dot-matrix printers use a head of pins; daisy-wheel printers were the older fully-formed-character type.

They persist for one reason the exam expects you to know: they are the only type that can print multi-part carbonless forms, because the impact goes through all the copies at once. Delivery notes, some invoices, and regulated forms still use them.

• Consumables are the ribbon and the tractor-feed paper.
• They are noisy and slow, and print quality is poor.
• Faults are mechanical: a worn ribbon gives faint print, a stuck pin gives a persistent white line through every character, and misaligned tractor feed gives creeping vertical position.

Three-dimensional printers in scope for this exam: filament, resin and their consumables

CompTIA include 3D printing at a conceptual level. Two technologies:

• Filament printers melt a plastic filament and lay it down layer by layer. The consumable is the filament spool. The components to name are the extruder and hot end, the heated bed, and the motion system. Common faults are adhesion failure — the print detaching from the bed — and clogged or jammed extrusion.
• Resin printers cure liquid photopolymer with light, layer by layer. The consumable is the resin, and it produces far finer detail. Resin is an irritant and requires gloves, ventilation, and a washing and curing step after printing.

The general points that carry: the print requires a model sliced into layers by software before printing, print time is long, and bed levelling or calibration is the most common cause of failed prints on filament machines.

Consumables, duty cycles and the maintenance a printer expects on a schedule

Every printer type has consumables, and matching type to consumable is examinable:

Duty cycle is the manufacturer's maximum pages per month, and the recommended monthly volume is usually a small fraction of it. A printer run at its duty cycle continuously will fail early, and recommending a printer whose recommended volume is far below the customer's actual use is one of the most common purchasing mistakes in small offices.

Scheduled maintenance, which the exam expects a technician to perform rather than ignore:

• Laser: replace maintenance kits at their stated page count — typically fuser and rollers — clean the paper path, and use a toner-safe vacuum.
• Inkjet: run the cleaning cycle when quality drops rather than routinely, keep the machine used, and calibrate after cartridge changes.
• Thermal: clean the head with the recommended solution and clear adhesive residue from label paths.
• Impact: replace the ribbon before print fades badly, and check the head for stuck pins.
• All types: clear the paper path properly, keep the firmware current, and keep a record of consumable changes so wear can be predicted rather than discovered.