HP Integral : running !

The printers in the HP150 (original version, the 150-II doesn't have a built-in printer) and in the terminals is, I think, fairly similar to the 2671 (the number 2674 seems to ring a bell, but I can't remember why). Alas the technical manual for the HP150 doesn't include anything on the printer other than the pinout of the connector on the 'frontplane' (HP's term, not mione). The 9845 printer is totally different. For one thing the 9845 has a single row printhead the full width of the paper, the 2971 has a 1 dot wide printhead that moves back and forth. The 9845 printer electronics is also somewhat strange. It microsteps that stepper motor -- the board the printer actually plugs into (and which has one of the monitor connectors on top) is mostly the stepper motor driver and PSU. The warning about 'High Voltage Transients' on that PCB's heatsink applies even when the motor is not turning -- it's a sort of SMPSU, variable pulse width, to do the microstepping. The printhead is electrically a long shift register. There are 7 driver hybrids, each driving 80 print elements, linked end-to-end. If you have a 9845 printer it's worth slipping the printhead out (disconnect the earthing braid, unplug the cable, undo the 2 screws and locating cams), and then carefullly dismantling it. Put it down paper-side up (support it on the metalwork, not on the camacitors that sick out of the front face), undo the 6 screws (not all the same length), then lift off the rear block. You'll now see the 7 driver hybrids, carefully remove those, then the 35 zebra strips (2 lengths), the plastic frame. Disconnect the DIL plugs from the PCB (these carry the prinhead common wires), take out the PCB. It's a typical HP (of the time) build. Mechanically beautiful. I don;t know.... It has one good feature, though. Since the inputs to the chopper transistors are transformer-isolated (the little pot-core transformers on the chopper PCB), all the control circuitry is on the output sideo of the isolation harrier. This makes it a lot easier to work on, IMHO. BTW, there are 4 LEDs on the control board, visible through a slot in the cover. These should all be on -- they're connected to the +ve and -ve PSU control board supplies (I can't rememebr if before or after the 3-terminal regualtors) and one supply derrived from each main chopper. If either of the former are out (in which case the 2 choppers will also shut down), there;s a fuse on the PSU mainboard for them, a 3AG cartridge for the +ve rail, a picofuse for the -ve rail. If those supplies are OK and both choppers have shut down, then it's possible the protection cicuit, based round all 12 comparators in the LM339s on the control board, has triggered. I've never had that problen. I have has the PCB tracks corrode and disapper (and you can't solder them....) Me too. Yes. I have the Thinkjet service manual, the carriage/cable is a listed spare part (I don't think I ever mananged to get the cable on its own, even though it's not hard to unclip the bits of the carriage and slip a new cable in). AFAIK HP no longer have any parts for the Thinkjets, though. If you are taking the carriage out, make sure the ends of the drive wire don't come off that TX7 screw that goes into the bottom of the carriage. There's a plastic wasker to make sure this doesn't happen. HP say that you can't retrhead the cable, and have to replace the entire mechanical chassis if this happens. Well, you _can_ rethread it (Duh, I mean, it was assembled from separate parts originally), but it's a right pain to do. I had to do it when I had to remove the cable to repair the carriage feed gearbox in one of my TJs, but I don't wnat to do it again! Ditto for the 2 stepper motors (which are electrically the same in the Integral as in the mains-powered Thinkjets, battery powered Thinkjets have different motors). The Integral's ones have longer leads. That's easier to kludge -- you can cut the wires off the old stepper and solder them to the wires from a stepper raided from a normal Thinkjet. Not that I've ever had to replace a stepper motor in a Thinkjet. -tony