HP Integral : running !

[Tony Duell]

>    I've been wondering, how similar is the printer in the 9845 to the one
> in the 2671 and to the optional ones used in the HP-150 and the ones used
> in the old HP terminals?

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.


> 
> >
> >[1] I haev just finished figuring out the PSU. It's quite the most 
> >complicated one I have ever worked on. 2 main choppers (each with 2 
> >transsitors in push-pull), 3 more switching regulators on the LV side, 5 
> >chopper control ICs, overvoltage comparators on all outputs, Eeek. 17 ICs 
> >on the contorl board (including the PIC6xx choppers), 16 transistors on 
> >the main chopper board, and so on...
> 
>   Eeck!  Why does HP always over complicate their PSUs!
> 

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.


> >
> >> The Thinkjet is ok but it leaks and/or dries up (Usually both!) if you
> >
> >I have had a few 'normal' Thinkjets in for repair where leaking ink has 
> >corroded and ruined the flexiprint cable that goes from the carriage (and 
> >carries the contacts for the cartridge) to the main PCB. I have never 
> >found a way of repairing this PCB.
> 
>    The contacts are formed from little copper tits that seem to be lightly
> glued to the cable and I've found that if you WIPE the contact area of the
> cable that you will most likely wipe the contacts right off of it. If I
> have to clean one I rinse it a LOT and GENTLY blot it.

I've never had that problen. I have has the PCB tracks corrode and 
disapper (and you can't solder them....)

> 
> 
> >
> >On a 'normal' Thinkjet you can raid the part from any other Thinkjet, so 
> >you can, say, use a fairly useless RS232 one to fix an HPIL one, useful 
> >on the HP71, etc. 
> 
>  Yeap. I've been hoarding ThinkJets for that very reason. I used to order

Me too.

> the flex cables for the standard ThinkJets for something like $7 and they
> would deliver them overnight via FedEx!  I haven't ordered one in years and
> I'm told that they're out of them now.

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!

> But although the Integral's Thinkjet is electrically 
> >the same, the mechanical layout is different, and the cables between the 
> >PCB and the mechanism are longer -- including this flexible PCB. 
> 
>   Yeap, I've looked at both cables side by side and they're the same except
> the IPC cable is about twice as long. I suppose that if you got desperate

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