Resetting the Samsung SCX-4200 / SCX-4220 cartridge chip: a two-resistor programmer and PonyProg

Our Samsung SCX-4220 printer stopped printing: the cartridge was "empty" even though we had refilled the toner. The reason is the chip on the cartridge. It counts pages, and once the counter reaches its limit, the printer no longer accepts the cartridge. The chip is an ordinary 512-byte EEPROM that can be read and rewritten with a two-resistor programmer.

This article covers the Samsung SCX-4200 / SCX-4220 printers and the SCX-D4200A cartridge (on the chip it calls itself C4200EXP). The method still works: the printers are alive, while original cartridges have not been sold for a long time.

What to do with the chip

1. Read the chip and save a copy before changing anything.
2. Clear the counters and marks that tell the printer the cartridge is used.
3. Change the cartridge serial number.
4. Write the chip, insert the cartridge, print a report.

You still have to refill the toner: the chip only tells the printer the cartridge is new, it adds no toner.

A two-resistor programmer

The simplest programmer for this chip: a COM port (DB9) connector, two resistors and 5 V from USB. The software is PonyProg in SI Prog mode.

• Resistors from 1 to 10 kΩ. Ours were about 9.5 kΩ and it worked.
• The VCC, SCL, SDA, GND labels are printed on the chip board itself. You can leave the chip in the cartridge: solder or press the wires onto the pads.
• Power is 5 V only. If you take it from a PC power supply, use the red wire (+5 V), not the yellow one (+12 V will kill the chip).

A modern computer. Motherboards often have no COM port any more, and cheap USB–COM adapters work badly or not at all with PonyProg in SI Prog mode: the software drives the port pins directly, and an adapter cannot do that. What is left:

• an old computer with a COM port, or a COM port expansion card;
• a CH341A USB programmer: it supports 24Cxx memory, and the chip connects to it the same way, with four wires (VCC, GND, SCL, SDA). No resistors are needed then, and you use the software that comes with the programmer.

In 2014 everything worked for us through the motherboard COM port under Windows 8 x64, with no emulators.

Reading the chip in PonyProg

PonyProg is free; get it from the official project page.

1. Hardware setup: serial port, SI Prog API interface, your COM port. Leave the inversion boxes unticked.
2. Calibration: once, from the same menu.
3. Device type: I2C Bus 8bit eeprom, then 24XX Auto (or 2404). The size should be 512 bytes.
4. Read. If the wiring is right, data appears and the first line shows the text C4200EXP.
5. Save the file right away (.e2p): this is your backup. If anything goes wrong, you can write it back.

What the bytes mean

All the useful information is in the first 128 bytes. The rest is FF, apart from the chip maker's signature near the end. Here is what we changed (addresses in hex):

Notes:

• The serial number must change. The printer remembers the cartridge numbers it has already seen. It may reject the same number with cleared counters. The simplest way is to add one to the last digit. The number is digits only; do not put letters in it.
• The install mark goes: a new chip does not have it, and the printer writes it itself when it sees the cartridge for the first time. It also increments the toner replacement counter then.
• Capacity: there is no point in setting more than the refilled toner can actually print.
• The page counters at 4A–4F we left alone, and the report after flashing showed 1486 pages for the cartridge: that is 05CE. It did not stop the printer. If you want the report to show zero, clear them too.
• Do not change the region (EXP): it must match the printer's region.

Then write the chip; PonyProg verifies the write itself. Insert the cartridge, and the printer prints.

The printer report before and after

The "System Data List" report is printed from the printer menu, in the reports section. At the bottom are the cartridge counters and its serial number.

The printer starts printing halfway down the page

A separate fault of these printers, unrelated to the chip. Over time the printer starts printing not from the top of the sheet but from the middle: the top half of the page is blank, and the text slides down or is cut off.

The cause is a small foam "bumper" in the paper feed mechanism. It is there to damp the click of the mechanism. Over the years the foam becomes sticky. Instead of damping the hit, it glues the mechanism to itself, and the mechanism comes free late. The sheet starts moving later than the printer starts printing, so the print lands in the middle of the page.

What to do:

• find the bumper next to the mechanism that clicks when a sheet starts feeding;
• clean and wash it and the surface it sticks to: first remove the sticky layer (isopropyl alcohol on a cotton bud), then wash the foam in warm soapy water;
• let it dry completely and put it back;
• if the foam crumbles, replace it with a piece of similar soft foam or felt of the same size.

After cleaning the click is quiet again, and printing starts at the top of the sheet.

Article changelog