LJ4 VFD (was Re: On collecting printers...)

Fellow HP printer collectors and repairers, I can't seem to find the exact message now, but in the recent thread about printer collectors, someone mentioned stripping various parts from the LJ4 series, especially the VFD. As it so happens, just today, I did just that to a printer that was going to the scrap pile (I know where the printer came from, and it is mechanically worn out - several hundred thousand pages). I play with LCD and VFD modules for the LCDproc project, and know all about the "standard" HD44780 chip used to control many, many character-based modules. We even have a few devices around the shop that used these standard modules. The LJ4, though, does not. It has a "bare" VFD, 60 pins for a 1x16 display, then the usual HV PSU components plus the 8 buttons and 3 LEDs and what looks like a Toshiba MCU, all on the same board (marked RG5-0841 and S-10437D and 3090741-01). The only connection to the board is a 10-pin 0.1" connector (like the ones used by a DEC DLV11J or a PC motherboard for serial), so presumably, it takes in +5V and has a ground connection, leaving 8 pins for some random, potentially proprietary scheme for bidirectional communication. I'm sure I could gain some minor insight to the electrical connection by poring over detailed-enough schematics (not possible at the moment because we are having problems with our ground station), but even if it turns out to be some sort of clock-and-data SPI arrangement, it wouldn't tell me anything about the software protocol to talk to the printer. I don't have a logic analyzer on hand, so monitoring the traffic to a live printer isn't going to be easily done. For those that have delved deeply into the secrets of HP LaserJet printers, is there enough documentation out there on how the front panel communicates with the rest of the printer to not have to discover everything from scratch? 1x16 VFDs are not really that expensive - compared to tens of hours of investigation, they are really quite cheap. Larger VFDs can be pricey, but even those can be had for $20 or so, if you check places like BG Micro and Electronic Goldmine a few times a year. It would be fun to talk to this printer front-panel, but without a starting point, I think it would take so much time to figure out that all my other pending projects will cut in line in front of it for the forseeable future. So if anyone knows of any suitable documentation, I'd love to hear about it. -ethan -- Ethan Dicks, A-333-S Current South Pole Weather at 27-Jan-2008 at 20:20 Z South Pole Station PSC 468 Box 400 Temp -33.9 F (-36.6 C) Windchill -54.8 F (-48.2 C) APO AP 96598 Wind 6.6 kts Grid 78 Barometer 681.8 mb (10560 ft) Ethan.Dicks at usap.gov http://penguincentral.com/penguincentral.html