WIP. Rebuilding the HP 17440A Graphics Enhancement Cartridge for the HP 7440A ColorPro plotter. HP stopped making it decades ago; the design is fully recoverable from the service manual, so this is a from-scratch reproduction.
The cartridge is not a coprocessor. It is three chips on the plotter's 8051 bus — a
16K ROM in code space, a 2K SRAM in data space, and an address latch. All the arc,
circle and polygon-fill capability is firmware in the ROM, and that ROM has been
dumped. The stock plotter firmware adopts any board that answers 0xAA at code
address 0x8000, so no plotter modification is needed.
| Schematic | ✅ captured and building (pcb/) |
| Netlist | ✅ verified against the service sheets |
| ROM image | ✅ dumped, checksummed, ready to burn |
| Connector pinout | ✅ 1×22, 0.100 in — verify pins 12/15 with a meter |
| Board outline | ✅ measured, 3.35 × 2.36 in |
| PCB layout | ⬜ not started |
| Mating pin length | ⬜ needs measuring off a real plotter |
| Plastic shell | ⬜ undocumented, will need modelling |
| Built and tested | ⬜ |
REBUILD.md the full reverse-engineering writeup — start here
docs/
flashing.md how to burn the ROM
figures/ schematic regions and the component locator, re-rendered
manuals/ HP service manual and the two schematic sheets
firmware/ ROM images + checksums
pcb/ the schematic, as Zener source (diodeinc/pcb)
photos/ the bare PCA, and the cartridge installed in a plotter
archive/ the original zip these files came out of
cd pcb
pcb build hp17440a-gec.zen # elaborate + electrical checks
pcb bom hp17440a-gec.zen # bill of materials
pcb layout hp17440a-gec.zen # emit a KiCad project into ./layout- Measure the mating-pin depth in the plotter's cartridge bay.
- Confirm J6 pins 12 and 15 against 8051 pins 16 and 17 — HP's Service Sheet 7 has
the
WE'/RD'labels transposed and this design follows the corrected wiring. - Lay out the board and get one made.