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Service manual for plotter, HP/Agilent 'ColorPro' 7440A.

Discussion in 'Electronic Components' started by Lostgallifreyan, Aug 15, 2007.

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  1. Does anyone have the service manual for the HP/Agilent 'ColorPro' 7440A
    plotter? Also, the programming manual? I'll pay for either those, or good
    scans of them. eBay sellers aren't forcoming right now on that model.

    The most important bit of info I want is the details of power supply to the
    four pins on the connector. The label on the base suggests 20VAC at 2A, but
    that seems unlikely in extreme! There are no rectifying and smoothing
    components inside, and each of the four pins seems to have its own track.
    Two of them have a capacitance across them, too big to safely put directly
    across 20VAC. The conflict between label and reality is too great to trust
    to anything but original info. I don't want to risk reverse engineering
    unless no info can be had at all.

  2. Here is some 7440 info:


    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida

    CLFURENT Guest

    You can list your needs on "E-Bay WANTED". I did that for a manual I
    couldn't find - it took a few months but I hit the jackpot. My "listing"
    there is about 5 months old or more - and I still get hits from it for
    equipment with the same model number.
  4. I'm considering it, but as you say, it's possible to get mails indefinitely
    if the request is too braod so I want to try to get the information some
    other way first, even if just to narrow down what I ask for.

    One small breakthrough:

    That describes the right power supply, and it's the same for many devices.
    I'm trawling eBay for adaters/psu's for those, without much success, I
    found one in Canada (I'm in the UK).

    If anyone has any of those HP printers listed there, and is willing to get
    the PSU and let me know what the four pins are doing, i.e. which if any are
    commoned, or not connected, and especially, which are outputting 20VAC,
    that will be a great help to me.

  5. I've had about a 50% sucess rate with their online manuals, but it
    never hurts to check, and check back, because they keep adding more old
    manuals. They have some a lot older than 22 years on there. :)

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  6. Cool, I grant it's a nice way to look for stuff so I'll do it. Still hoping
    someone's got one of those PSU's to get me a pinout, but for the
    programming manual I can watch and wait, first thing is to get the thing
    started... Direct drawn PCB's. SMT, single sided and such. A cheap and
    effective way to make them, it seems. Good to learn with, if nothing else.
  7. Bob Pownall

    Bob Pownall Guest


    I have some contacts in HP's printing divisions. I'll ping them and see
    what I come up with.

    In another post, you indicate the plotter is a mid-1980's vintage. Is
    that correct?

    Bob Pownall
  8. Nice one. Thankyou. And yes, it is. I had a look inside yesterday, awesome
    thing, looks like it was made last week, not 22 years ago. No brittle
    plastics, wire sheaths are still flexibly plastic, no oxidised metal that I
    can see, belts are taut but not exerting strong constant strain, it looks
    like it could wait a century and still look good as new. Even the
    electrolytic caps look fine, but I won't know till I get power to it
    whether they are. I bet they are though.

  9. First of all, do you need 120 or 240 VAC input?

    I find several different supplies listed online: says 2V 2A, but doesn't
    say AC or DC. It also lists some HP printers that used the same supply,
    and I MIGHT have a 120 VAC input supply in my pile of dead printers. I
    also have some old HP plotters in storage that might use the same
    supply. says:
    Power connector:

    |o -> gnd
    |o -> ac1
    |o -> vcc
    |o -> ac2

    vcc and gnd -> 10Vdc @400mA

    ac1 and ac2 -> 20Vac @1A

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  10. Excellent find, that second info, it sort of confirms what I suspected, two
    power busses. Hard to see why 4 pins otherwise. Also, that capacitance I
    detected would likely be extra smoothing for the DC buss.

    I'm after a 240V input PSU but I suspect cracking open the case might show
    a dual-primary transformer.
  11. Been inside. That info checks out, pretty much, except that's 2A as claimed
    by the other source, there's a bridge rectifier made of 4 diodes, and a 50V
    2200µF cap before a 2A fusible resistor protecting what comes next. The
    other cap is a 3300µF so I guess the PSU is unusual in rectifying a 10V or
    12V winding but not smoothing it.

    I guess this is part of some common standard HP wanted so they could use
    the same PSU on so many devices.

    I could probably wire something up now but this HP 7440A plotter is so
    awesomely perfect I want to treat it nice, so I'll try to get service and
    programming manuals and original PSU if I can. I'll try the eBay wanted ad
    soon if I don't get lucky here.
  12. Bob Pownall

    Bob Pownall Guest

    Lostgallifreyan wrote:

    The first response I got back listed these (non-HP) sources: > Manual&cat=printers > Manual&cat=printers

    Since you've already said you're willing to pay for manuals, these (or
    something like them) might be your best option.

    Bob Pownall
  13. Thankyou. I'm willing to pay, but I'll pass on those, having looked at
    them. They might not have any. Even if they do, they'll set the price to as
    high as they like the momemt I request a quote, then add all the surcharges
    and handling charges and brokerage charges they can think of.

    I'll wait till someone on eBay offers one. Can't negotiate with people who
    run vast virtual carts. Maybe on eBay, I can. eBay also contractually binds
    a seller to have the item before trying to sell it for a start.
  14. LONG post alert. >:) Might be instructive though, or at least, amusing.
    I just tried one of these strange outfits that say they have, or can get
    parts. First one I tried for the part in question, and sure enough, it
    really IS that bad! Read on if you're bored enough.....

    Hi, I saw this on your site:
    Caritronics K-3000 TRANSFORMER PLY HV 3000VDC FS $87.00
    Can you tell me any specs for it? 3000VDC is nice but how much current? I'd
    need to know before deciding on anything.
    Any info at all is welcome.
    [Company details omitted, this is a fun post, not investigative journalism]
    No, you don't need any of that. If you have the part, AND information to
    help me choose, I might be able to decide to buy. If you ask me for
    information that doesn't help me find the part or information about it, I
    won't go there, it's a waste of time, and a potential annoyance.
    If you're able to get info on that part, just reply by mail as you already
    did, that's all you need. None of that other stuff is needed, no-one buys
    parts that way, they just buy parts. IF the information about them is
    forthcoming without obstacles, otherwise they go elsewhere.
    Awesome! I found a couple for less than $50 including postage. I knew you
    weren't for real, and you just confirmed it MAGNIFICENTLY. What kind of
    outfit are you, really?
    You don't have the parts, do you, or even any access to them at all? You
    don't know a thing about them, do you? They don't weigh 3 lb each either,
    so you might want to correct that little detail on your site.
    Let me guess, you're one of these middlemen outfits who try to profit by
    inserting themselves between people and the things they are looking for, a
    bounty hunter for stupid people who don't really know what they want and
    have far too much of other people's money to spend. I'd have the same
    change trying to buy this part from a Nigerian email scammer, I imagine.
  15. PopMed

    PopMed Guest

    I just joined the group today. I noticed that you are searching for a
    power adapter (or mains
    adapter depending on which side of the pond you're on) for an HP7440a
    plotter or at least info on
    power requirements.

    Here is the link for the service manual from the very helpful and
    useful HP Museum (mentioned in
    Curt Carpenter's article in Circuit Cellar #202 about using the 7440a
    to do direct PC board resist

    I'm glad to have looked at this documentation since I was about to
    hook up a 20 vac transformer
    paralleling the inner and outer pair of pins as suggested by some
    forum on the net. This would have
    shorted the secondary winding(s) with unpleasant results. Actually
    paralleling any two pairs would
    guarantee shorting some part of the secondary.

    The nitty gritty of the power supply:

    --the transformer comes in many models to match the rated 100, 120,
    220 and 240 input range. The
    secondary is 20 volts AC around 2A with a center tap of 10 volts AC--
    and it must be a true center
    tap. If asymmetrical, one half of the winding will shoulder all of
    the digital circuitry load and the other will loaf along.
    --the 20 vac is fed to a full wave bridge to C33 a 2200 uf filter
    capacitor to produce approx 26 vdc unregulated to drive the motors.
    This voltage is also monitored by support ic U6 which adjusts the gain
    of the plotter drive circuits to compensate for line voltage
    --the center tap produces a nominal 10 vdc through a center tap full
    wave arrangements (ie using two
    diodes) to power the digital logic. The circuit is a departure from
    the conventional (and more familiar) one which grounds thecenter tap
    and places a diode in each leg of the transformer secondary joining up
    at the filter cap. HP chose cleverly to connect the center tap
    directly to C32 a 3300 uf filter cap and ground each leg of the
    secondary through its own diode. The cleverness emerges when it
    becomes clear that these grounding diodes are already part of the full
    wave bridge! All of the necessary free-wheeling is already present to
    isolate the two full wave supplies and to prevent discharging any
    filter cap through a secondary winding.
    --the on-board power supply has a charge pump to generate -9 vdc used
    by the encoders and RS232

    To understand all of this more easily I would recommend printing out
    the schematics. They are complete but because of their size they are
    broken up into sections. To prevent serious migraines I would
    recommend trimming and taping together the sections so that the entire
    power supply circuit paths can be viewed at once. Note that there are
    two versions of the 7440a. Option 001 is RS232 and Option 002 is
    HPIB. The RS232 version's power supply simply adds one current limited
    +9v supply for the serial interface. I sincerely hope you don't have
    the HPIB version unless your computer speaks this protocol!

    The Bottom Line:
    --find an original adapter. PRO: guaranteed compatibility CON:
    limited availability and
    unlimited price!
    --find a suitable transformer with appropriate primary voltage and 20
    vac center tapped with a 2A
    rating. PRO: certainly cheaper and will likely work especially when
    care is used to make proper
    connector pin hookups CON: not a common voltage/current rating
    especially center tapped
    --find two identical transformers each with a single 10 vac winding at
    2A and wire in series (wire
    the primaries in parallel of course and check the phase of the
    secondaries) PRO: more likely to
    find these transformers (you may even have them in your junk box or
    spares bin) CON: care must be
    taken to turn both transformers on and off simultaneously so that
    digital and motor drive circuits
    will do likewise, additionally there is the temptation to use 12.6 vac
    transformers which may
    produce excessive voltage from the full wave bridge especially since
    this voltage is continually
    monitored by U6. I would avoid this temptation and I decline to take
    responsibility for any
    information in this post -- use at own risk!
    --find a non-center tapped 20 vac 2A secondary and use to power the
    full wave bridge while using an
    independent 10 vdc (must be DC!) at approx 0.5A source connected to
    the positive end of C32 the 3300 uf cap (with the negative end of the
    source connected to circuit ground of course) PRO: presents another
    availability and reasonable-cost option CON: the same caution about
    powering everyhing up and down at the same time.

    The choice is yours. I have deliberately left out pin number
    references. Powering up this device
    in any do-it-yourself manner is not a cookbook proposition. Complete
    understanding of what you are
    doing and a healthy measure of experience are required. Good luck and
    proceed at your own risk!
  16. My hero! And I don't even beleive in them. Thankyou, that is very awesome,
    an amazing stash.

    I agree, finding the original adapter seemed wise once I learned of the
    unusual arrangement of 4 terminals. Even with the centre tap the fourth
    terminal is not yet clear to me, but it will be with those schematics.

    I got a supply, WITH a deskjet printer. :) Won it on eBay for the cost of
    postage, I added a couple of quid because no-one else bid and the seller
    was willing to change his postage conditions to send it to me.

    If I do have to make a second supply, I'd probably use a 12V 2A toroidal
    and take out enough turns to drop the voltage. As they have two separate
    secondaries, they are ideal for this.

    I got lucky btw, NEW (mothballed) ex-MoD (Navy) device with RS-232. It
    looks and works like it was built last week, not over 20 years ago. Got it
    for price of postage, again, only thing wrong was no power supply.

    With 8 Staedtler Lumocolor refills and a few Lumocolur pens to raid various
    width tips from to refit plotter pens with, I'll be making boards soon.
  17. Dave Platt

    Dave Platt Guest

    There's a service tweak I discovered/invented for these plotters which
    you might possibly find useful.

    The paper motion (in the "Y" direction) uses several cylindrical
    rubber wheels, which hold the paper against individual rollers on the
    other side the paper. On the used plotter I bought, the plotter had
    been stored with the paper drive mechanism in the "engaged" position,
    and the pressure from the rollers had flattened the rubber on the
    wheels enough to create a distinct "dimple". This caused paper
    motion to be uneven and unreliable - the roller/wheel interface would
    lose pressure when the roller hit the dimple in the rubber.

    Trying to buy replacement wheels from HP seemed out of the question.

    I found a solution at a local hobby store - a soft, flexible silicone-
    rubber tubing (translucent blue in color) which is used as a fuel line
    in radio-controlled airplanes. I was able to dismount the existing
    rubber-coated wheels and scrape off all of the old rubber (it's
    pressure-molded onto a ridged core/axle), cut off a short length of
    the silicone rubber tubing, and force the tubing over the core of the

    When re-mounted on the plotter, the new silicone-rubber wheel surface
    proved to work very well.
  18. Good cautionary point. I caught myself reading a manual the other day while
    leaving the paper engaged, and disengaged it thinking of exactly that
    problem. I'm slightly conditioned to thinking of this risk and preventing
    it, having a bandsaw, those too can go agly if you leave them under tension
    and static for a significant period. I also used to repair tape decks...
    Nice idea. I think polyurethane might also be good, or that kryptonic stuff
    used for skateboard wheels, but not so easy to find in a tube, perhaps.
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