Journaling BrainFileSystem

I recently got a used laser printer (Canon LBP-4) from cit since he moved to Regensburg and sorted out some surplus hardware.

Having ordered a new toner for 23 Euros I had to notice that the printer is broken

The Display said 52 SERVICE and google told me that it’s probably the motor of the laser scanner.

So I grabbed the screwdriver and had a look into the printer.

outdated, but solid hardware

Some time ago they built hardware bigger, rugged, modular and with no SMD parts. Thus fixing stuff was easier.

The printer is such a piece of hardware consisting of modular non-SMD electronics. There are separate and removable circuit boards for parallel port interface, postscript processor and the printer control.

You can remove the circuit boards one by one and reassemble the stuff later quite easy.

Here are some photos:

The backplane:

Overview from above:

The postscript board:

The printer controller:

tuning the printer?

This controller is a 8bit microcontroller. It does 300 dpi. On the right you can see a fiber optic link. It’s used by the controller to detect the laser beam at a certain point before the 1st dot on the current line so that the controller can calculate the timing value for each pixel of the current line.

I thought about replacing the microcontroller with an Atmel ATMega32 for more accurate per-dot-timings to do 600 dpi, but tracing all the connections and reverse engineering the software would take quite some time I don’t have while studying for my diploma %-)

Well, let’s fix it first…

Also the printer does no more than 4 pages per minute, I wasn’t able to repair it without spare parts and I already got a newer printer, so there won’t be a 600dpi mod for the LBP-4
The Printer uses the Canon LBP-LX engine. The HP LaserJet 2P uses the same engine and there’s a repair howto for the 52 SERVICE error.

According to the wav samples from the repair page my motor should be ok. I thought about replacing the motor controller anyway, but it seems as if I threw away all my 5.25″ floppy drives a while ago.

tracing the problem

So I decided to measure the rotations per minute (should be 300 to 360 if I recall correctly) of the laser mirror motor by disconnecting the fiber optic link and attaching it to an IR-receiver-diode without a carrier frequency filter circuit, but with a daylight filter.

I wired the receiver diode in line with a 10k resistor between Vcc (5V) and GND and measured the voltage drop at the resistor with my oscilloscope.

It looked like this:

The Atmega32 and the IR transceiver diode are for another project and not used here.

Don’t mess with the laser radiation…

Since I didn’t want any laser radiation in my precious eyes, I put a blue bowl from the kitchen over the device:

The more IR-light you put into the diode, the more power from the resistor will be conducted to ground by the diode, the higher is the voltage drop at the resistor since more power can flow away to ground.

I tested it with the infrared remote control from my satellite receiver and noticed that the voltage drop is quite small, so I decreased the voltage range at the scope and got nice IR-spikes with the remote control.

However, I didn’t get even the smallest signal from the laser… Maybe it got a wavelength my receiver diode doesn’t support.

Disassembling the printer even more

New plan required. I removed the controller board and digged my way through the printer’s interior down to the laser and the scanner motor.

At the left of the black box you can see the laser board. The warning sign says (german text translated to english): Invisible laser radiation when open and safety lock bypassed %-)

So I opened the box – it looks like this:

I added the brown-white cable myself and soldered my IR receiver diode to it. Taped it directly to the laser outled, reassembled the printer to do a test drive and measured the IR light again.

Wrong wavelength

Nothing again. Since my receiver does 800 up to 1100 nm and IR laser diodes are usually at 730-780 nm it’s likely that I just didn’t get the wavelength of the laser diode.

I measured the voltage drop at the laser diode and got about 0.7V as far as I remember. Didn’t help me very much…

broken electrolytic capacitors?

The printer wasn’t in use during the last two years but it worked before – broken electrolytic capacitors usually are a good guess under these circumstances.
So the last thing I tried was to replace some possibly broken electrolytic capacitors. They looked like this: and were located on the laser board and the controller board.
I didn’t have some 33µF lying around so I used 47µF and gave it a try. Nothing changed.

Disconnecting the complete scanner motor board and/or the laser board didn’t lead to another error code either.

printer still broken, got a new one – struggling with CUPS

That makes locating the actual broken component quite difficult, so I consider the printer broken.

I got myself a new second-hand printer: An OKI Okipage 14ex that does up to 14 pages per minute. Well with 600 dpi and parallelport with ECP enabled it currently does 7 pages (containing graphics) per minute. But one shouldn’t use the plxmono filter recommened by cups. It’s deadly slow and does about 1 page in 10 minutes %-)

I’m using the l4jet driver with cups since the other driver cups offered for the printer didn’t do the shades of grey very well.

network printing, USB extension

Since I don’t want an extra PC in my living room, but I want to print via (VPN protected) Wireless LAN, I thought about buying a network card for the printer. But they’re deadly expensive, so I needed another solution.

I grabbed about 10 meters of my CAT7 reel, soldered USB connectors to it (used one twisted pair for the data wires, another one for Vcc and GND, shielding connected as well) and plugged it in my server in the basement and in the printer.

Unfortunately it doesn’t work very well… USB errors all over the dmesg after printing one page %-)

So I ordered a used Allnet Netprint IV without a power supply (but it uses regular 12 Volts) for 20 Euros including shipping costs. Let’s hope this will do the trick.

But now I’m literally looking at the black side for putting XGA to my self-built beamer through the two additional 10m CAT7 cables from the basement into the living room %-)