Forensic Report: Printer

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Examination

Forensic Questions

What does it do?
MFC-J6920DW is an all-in-one (combination fax, printer, scanner, copier) inkjet printer.

How does it work?

Inkjet printers containing thousands of tiny holes. These tiny openings drop microscopic droplets of ink onto the paper in the printer at a speed.

MFC printers by Brother use a liquid ink produced either by either a coloured dye or a liquid that contains solid pigments in suspension. As the print head moves horizontally in the machine, the paper passes through perpendicular to it. As the page passes through, the individual holes in the print head are activated, and a small drop of ink is pushed out onto the page. This process if performed at high speed with thousands of droplets that form together to recreate the digital text or image that is being transferred onto the media. For us, the overall image looks to be solid because the dots are so tiny.

Microscope view

On the other hand, scanners work by shining light at a document. In simple terms, the reflected light is then directed onto photosensitive technology via mirrors and lenses, then converted into electronic data that is used to form a digital copy of the original.

How it's built?

It is built up of three overall parts, one for scanning and one for printing. The top part consists of the image scan & fax scan and the bottom part consists of a printer and paper trays.

The casing is made of different types of plastic, ABS (Acrylonitrile butadiene styrene) which has mechanical properties such as impact resistance, toughness, and rigidity, PS-HI (Polysterine high Impact) a hard, solid plastic used frequently in products requiring certain rigidity, whilst offering elasticity and a good capacity for absorbing impact, POM (Polyoxymethylene) which is used for precision parts requiring high stiffness, low friction, and excellent dimensional stability and PPE-PS (Polyphenylene Ether + Polystyrene) which is a ductile material with excellent hydrolytic stability, flame resistance, and UV resistance. These properties make it ideal for applications in the process engineering, electrical, and medical industries.

When looking at the inside of the case, it consists of severel different mechanical and electronic parts with PC Boards, sensors and motors.

The parts inside are made of different materials, there are parts in plastic, metal, rubber, wire and felt absorbers.

Why it failed, or it wasn't used anymore?

The printer could be turned on and power supply to the unit was stable. Still, we could not perform a 'print or scan test' to determine what the actual issue was. Upon lighting up, the screen displayed messages and the touchscreen could be interacted with. There was an error message about connection to the server.

When disassembling the parts we couldn't find any faulty or broken parts that could contribute to issues of use.

A possible theory for failure could surround the maintenance unit. This component is designed to clean the printing carriage and make adjustments for precise printing. The component is made up of a pump, a gear box, sensors and different tubes to extract excess ink. The tubes appeared to be dried and perhaps were contributing to malfunction. Having a faulty maintenance unit could imply incorrect ink supply to the carriage which means it is dropping more ink than it needs to, or that printing precision could become affected.

Another theory we discussed could be revolving the sensors. The entire device is a body full of sensors to indicate where paper, ink or data are flowing to execute the desired task. These sensors play a critical role in helping the printer understand where things are located, in which state they are in, and if something is required to act upon in order to complete tasks. For example, moving paper from the bottom tray across the entire printing flow, or providing precise location for printing. Measuring and understanding the location of a picture or document inside the glass sheet upon scanning. Sensors are sensible and act with discrete voltage. If any of these sensors get burned, damaged or misbehave in anyway, then the printer will also have difficuly in executing commands and errors or issues can easily appear. We tested some of the sensors and found some to be somewhat unresponsive. However, most were working as expected and could not confirm that the malfunction came from this theory.

Motors, gears, mechanical components and general usability of inside components seemed healthy. Our hypothesis for failure was not necessarily validated and hence concluded that it is necessary to perfom additional tests to share a final conclusion. These tests could involve the image scanners, ink carriage or control boards.

Steps taken

Testing

After tearing the printer apart we saw a unclog small components that were part of the large pirating system. There were plenty of sensors/motors, from our uneducated opinion, which might’ve controlled the flow of paper, flow of ink, sensors for the size confirmation of paper.. etc. the printer is a very rich and intricate device that’s very complex in nature for how simple it’s main job is.

In the process of taking apart and testing, our ai was to figure out whether the components were functional or not , we had to learn the basics of electricity and currents. All electrical components have a certain voltage requirement. The amount/accuracy of the voltage needed is dependant on the type of component, it’s age, it’s function, and so on. For example the motors did not need any accurate voltage input for them to run, unlike the newer sensors which were designed to only withstand a certain amount of volts before getting fried.

Our tests started off with the power supply, which allowed us to control the amount of voltage that passes through a current. As well as a voltage reader to help us understand where the ground and positive routes were as well as whether a component was still “alive and well”. Our testing really showed the idea that too much might cause damage, as we manages to over strain one of the sensors and it ended up breaking. Later we tested for the functionality of a small motor which we deduced that it moved the papers inside the printer and we did not need to be careful with the amount of voltage -of course there would be a certain threshold but the more you add voltage the quicker it spins.

It was interesting to have the basic knowledge of circuits and currents, as it is a mahogany part of our every day life, which we do not see or interact with. It was also interesting to see the reaction of these sensors once they were “overcharged”. Identifying the materials and equipment needed to better control and manage these electronics and their capacities was quite rewarding. Also I think an important lesson we learned is that something may not be running because a small fuse might be blown out, it might be beneficial to learn more about how these machines run and function for our own personal gain.

Results

How many motors did we find inside?
Two Direct Current Motors
(RS445PV19120 Made in Vietnam)
Two Stepper Motors
(PM35S-F48-BKC5 Made in thailand)
(M35SP-11NK LF)

Does it contain a computer or microcontroller?
PC Board with power source
Main PC Board
Seperate PC Boards connected to the Main Board

Did you found any sensors?
LED Sensors and Switch Sensors

Sensors for paper supply
Sensors for paper transport
Sensors for paper size
Sensors for ink - quantities/ volume available?
Sensors for scanning - Locations in x axis

Conclusions

Opinions

What did you learn?

• How to break a device apart and learn from the process. To lose the fear of the black box, and learn how different aspects of technology work.
• These devices are complex integrate systems, components and technology that make printers almost as robust as a full function computer.
• Printers print by expulsing ink through tiny holes at a very precise speed, location and volume.
• Printers have many systems inside them, including electrical, mechanical, power units and control boards.
• Ink dispensing systems are complex and interesting, consisting of tubes, pumps, sensors and motors that work together.
• Printers integrate both humand and digital inputs and outputs.

What surprised you?

• The number of parts and components that make up a printer.
• How the scanner understands location through measuring lines across an axis.
• A lot of ink is wasted during maintenance and ink absorber boxes are almost full. It really makes you wonder what the incentives behind this functions are, understanding that the company makes money by selling ink.
• Sensors play a critical role in printing, and there are a lot of them.
• The quantity of plastic parts is excessive but makes sense.
• The complexity of plastic parts, this only makes sense if the company can sell a lot of printers.
• The complexity of processes and systems involved in printing or scanning.
• The diverse forms of assembly (screws, plastic fasteners, wire clips).
• Low price for a printer that actually very complex and has so much going on.

Images