Dissertation on HP Desket Printer Repair
These comments are in response to: "Repair
Brief #49 - Part 1: HP DeskJet Professional Printer - Dead"
and its followups. My text is indented. See those articles for details.
The quick summary is that I picked up this printer at a garage sale
and first had to dry it out and repair some cold solder joints before
it would print at all.
(From: Paul Grohe (grohe@galaxy.nsc.com).)
I've dealt with a few of these buggers before!
;^)
Is yours a DeskJet, DeskJet Plus, or any of the
DeskJet 500 or 600 series?
I believe it to be an original DeskJet. If not,
then ...well....then I may as well tell you this anyways because
you will probably run into these some day....(some of the below
can apply to other ink-jet printers).
Now, how to do a self test? Fortunately, the complete
HP users' manual was part of the deal. "Hold the FONT button
while turning on power". OK, no problem.
Try holding down 'FF' during power-up, you may
get a different test page. One of the pages should have a jet-test
pattern (A slanted diagonal line separated by 11 vertical marker
lines and little jet ID numbers).
The first page of the standard self test results
in that pattern.
I first tried the cartridge that looks exactly
the same as the one that came with the printer (though the part
number is different). Then, I tried another somewhat larger one
that apparently has identical connections.
The different part numbers are the 'standard capacity'
and the 'high capacity' cartridges. They're interchangeable.
Going back and forth, they are consistent. I am
not sure if one of the two missing lines are the same on both cartridges.
Could something be marginal or is the priming not working? However,
all other nozzles seem to be rock solid. Reseating the connectors
to the print head makes no difference. If I knew which drivers were
involved I could look at the signals but it will be difficult to
trace the circuitry from the driver board to the actual nozzle.
I assume you have cleaned the contacts (with a
Q-tip, on both cartridge and socket). Use a magnifying glass and
check *each* of the gold 'bump' contacts. Repeated cartridge swapping,
or improper insertion, can cause a crack to form around the base
of the 'bump' and the pad (or the pad and the trace). The 'bumps'
can also be 'flattened' by cartridges that were forced in at too
much of an angle. There should also be some 'give' or 'sponginess'
to the contact area to assure even contact with the cartridge.
Check for broken/bad traces in the flex-cable
that goes from the driver board to the cartridge. Ohm out the cable
between the supply commons and the individual driver lines (at the
PCB) with the cartridge in place. I think the jet resistance was
about 50 ohms (It's been a while). There were four separate jet
sections (commons). All four commons were tied to the +20V supply
through four separate (12 ohm?) series current limiting resistors.
The driver outputs seemed to be grounded emitter, open collector
(w/clamp diode?). The jets themselves are driven individually and
are not multiplexed.
To test, I printed an all-black page (with an
empty, but installed cartridge) and watched for activity on each
of the lines at the PCB end. Good pulses are 'bi-levelish'. Normally
negative going 20V, with pulses down around 15V, and going all the
way near ground for that particular jet. The commons 'bounce' because
of the shared series current limiting resistor, causing the numerous
smaller pulses around 15V (caused by the firing of other jets sharing
that common). A bad connection will show up as a weak or distorted
pulse. An open or broken line will show up as 0V. I theorize that
a bad driver would show just the smaller 'line bounce' 15V pulses
and a shorted driver would show 'GND' (and also would blow out that
jet!).
The current involved to drive the 'jets' is a
pulse of short duration and pretty high current. Any poor connections
will cause excessive I/R drop and the jet may not fire hard enough.
A sign of this is drops (dribbles) of ink that form on the head
during printing.
While you are in there, check and clean the rectangular
rubber seat that the cartridge rests on in the 'parked' position.
Dry ink can cake up on it, causing a faulty seal and resulting in
dried-up cartridges ($$$!). The rubber seat pulls off and is easily
cleaned with a wet paper towel (wear gloves, or you will suffer
the dreaded 'black finger syndrome'). Also clean the 'nose wiper'
that sticks up about a centimeter to the left of the cartridge seat.
This always cakes up and can cause printing problems.
To manually prime an uncooperative cartridge,
you do not have to suck on the business end. You can gently blow
into the top vent (located on the top of the cartridge, inside the
green arrow) to prime it. But be careful!; If the jets are severely
plugged, ink may blow out the check-valve on the bottom (under the
plastic 'flap' with the 'maze-like' area). Very messy! Have a towel
ready!
The old DeskJets were (and still are) notorious
for paper feed problems as they age. This is caused by the three
big paper pick-up rollers drying out and becoming hard and smooth.
Roughen them up with some rough sandpaper. The HP FTP site has a
article about this in the DeskJet DOC directory. A free kit is available
from HP (to qualifying S/N#'s) that 'dresses' the rollers (basically
forces the rollers to turn and sandpapers them).
OH! Biggie! Another big 'failure mode' of the
early printers is that the paper sensor lever will jump out of position
and jam if the printer has suffered some rough handling (especially
if it was turned upside-down or on it's side). The paper sensor
lever (pivot) is located on top above the middle roller. The other
end breaks the beam of a photosensor. The 'interrupter' end will
move over just enough to wedge itself above the photosensor. This
is cured by simply raising the lid and wiggling it until it drops
back into position (I have 'fixed' many an alleged 'broken' printer
this way). The 'interrupter' end seems to have been made larger
on the later printers to prevent this.
From time-to-time, the cartridge's nose should
be wiped clean with a soft, moderately damp cloth (~ every 100 pages).
Keep the 'business' end pointed down when handling/cleaning the
cartridge (Yes, this means hold it above you and clean it from the
bottom!). This keeps the galleys and jets primed.
Comments: I suspect the original problem resulting
in the dead printer to have been a cold solder joint on the DC power
connector which I repaired. I don't really think that the nozzle
problem was caused by the water since the print head driver board
was never wet. Since the data connection to the print head driver
board is a 20 pin cable, this must be a common bus and thus it is
unlikely that any failure on the main logic board could manifest
itself as a single or pair of bad nozzles. Stay tuned.
I concur. If just *one* jet is not firing, then
it is on the driver/flex- cable/connector/cartridge side. All the
nozzle decoding is done on the driver board, so the 20 pin interconnect
cable is okay. The DC (well..really 20VAC) power connector does
take some abuse in normal service, this could have aggravated the
cold joint.
Don't forget to check the buttons for water damage/contamination.
Been there, done that. The FONT button was Coke-logged.
Do you know what the difference is between the
DeskJet and PaintJet cartridges? There is at least one contact that
is open on a DeskJet cartridge and wired to something on a PaintJet
cartridge.
I also have a color PaintJet 300 with a possible
"dead" driver line, but I focused my attention to the
ailing DJ500, so I did not have a chance to "buzz-out"
the PaintJet cartridge. From looking at it, it looks like the PaintJets
are multiplexed in some way (there are more jets/contacts than wires
in the flex-cable). I never got around to fixing/looking into it
(it's still sitting there).
BTW 1; The DeskJet, DeskJet Plus and DeskJet 500
(non 'C' models) are basically the same (except for some internal
fonts). The DeskJets speak PCL, so if a driver for a DeskJet is
not available, you can use a basic HP LaserJet driver (but the margins
may be cut off, as the DeskJets print area is not as big).
The missing line problem turned out to be bad
connections between the flex cable and the gold contacts on the
print cartridge due to the flex cable shifting position on its indexing
pads.
These things are so damn simple that not much
can happen to them. I have yet to run across one with a severe electrical
problem. They are always minor mechanical failures (or missing power
bricks...$35 from HP).
As noted previously, the HP DeskJet series in
general is a well engineered design with only a half dozen basic
components. While my (DeskJet) printer is one of the oldest models,
the fundamental design has not really changed dramatically in the
last several years as evidenced by the fact that print cartridges
for some much more modern printers work just fine in this old machine.
All the DeskJet/DeskWriter printers, up to and including the 6X0
series, use the same B&W cartridge as the original DeskJet.
Those cartridges will still be available for some time. Your printers
life is not over any time soon!
The print quality with a new cartridge is nearly
laser-quality. Yes, HP seems to come out with a new, faster, cheaper,
color. etc. printer every few weeks. But, looking inside newer printers
shows that their basic design and construction is quite similar.
The DeskJets are good, sturdy and reliable printers (as long as
they are well maintained) You did clean the rubber cartridge seat
and flap. Right?.
BTW 2: For maximum cartridge life, make liberal
use of the "draft" setting for "not-so-important"
printouts (or, er, um, drafts!). It also prints faster because it
"swipes" once per line instead of twice.
BTW 3: Use the cheap 'Shark' brand inkjet paper
for best results. Pretty near laser quality! Regular copy paper
tends to bleed, but is fine for general use.
Can you tell I have a 'few' of these printers
around???? ;^)
Just when I thought all was well....
At random times, the print will fade out and require
priming by mouth to restore operation. This can be anywhere from
a few lines to a few pages. Until it quits there is no evidence
of a problem. Blowing into the vent hole will restore operation.
This happens with more than one cartridge. It appears as though
the ink is just not refilling after being vaporized.
Is the cartridge full? As you get down to the
last 20% or so of the cartridges capacity, it tends to start doing
this. I guess there is not enough pressure "from above"
to force the ink down. If you can start seeing through the cartridge,
you are probably near this point.
CAUTION: I found out the hard way that you really
do not want to stick anything into the vent hole - ink all over
the place as the vent valve must have been damaged by this mischief.
I 'salvaged' the cartridge with a blob of silicone sealer. I don't
know what the long terms implications of this 'repair' will be.
In troubleshooting the printer, you tend to "burn
up" cartridges a *lot* faster than in normal use.
I cleaned out the priming tube which was *totally*
clogged with dried ink and it seems to be much happier now.
This can be a symptom of the print head not seating firmly when
in the "parked" position. Use a dental mirror and make
sure the seat presses firmly against the head. One cause of this
can be turning off the printer before it has a chance to run through
all of it's "housekeeping" cycles at power-up, reset (re-boot),
or after printing. During certain parts of the cycle, the head is
moved slightly, or the cover is moved. Turning off the printer too
soon may leave the head exposed. Always let it finish, then turn
it off (warn others about this).
If you haven't already, just pull the thing apart
and give it a good overhaul (get your favorite pair of Torx bits
ready!). Clean all the rubber tires, seals and "nose wipers".
Wipe off the slider bar to remove any old lubrication. If there
was a serious ink leak and the printer was involved in some "circus
acrobatics", some of the ink can get on the slider bar and
contaminate the factory lubrication, causing it to become "pasty".
I wipe the slider bar clean with a cloth then apply a *light* coating
of a light, teflon-type machine oil with a cloth (I use "Tri-Flow",
a spray-on type usually found in bike shops).
BTW 4: In the winter months, with it's low humidity,
the rollers will shrink even more, causing even more paper feed
problems. This is also compounded by the fact that the paper sometimes
develops a static charge and tends to "stick" together.
Sometimes it pulls two or three sheets in at once, or the paper
sticks firmly together in the tray and the weak, dry rollers cannot
pull the paper in. Just remove the stack of paper and "fan"
it out to loosen it (especially if it has been sitting there unused
for a couple of weeks).
These printers are, like some other things we
won't mention, 'Use `em or loose `em'! They work best with frequent
use. They do not like sitting around for months unused. Three months
seems to be the limit before a 'good' printer will start to dry
up from no use.
Before I 'discovered' the priming problem, I has
visions of a serious electronic problem like an intermittent resulting
in the nozzle drive pulses getting messed up at random times.
How is pulse width determined in these things?
I never really investigated the timing of the
pulses. I'm not sure how they vary the pulse width. I looked at
the pulses when it was doing the first page of the self test, which
is mostly text, and all the pulses seemed to be the same width.
The conclusion: After several years of faithful
service (the most serious problem being that I really used the printer
so infrequently that the cartridges invariably dried up!), I was
given an HP DJ1000C with a couple of broken plastic tangs to which
the pressure roller springs were attached. Some overzealous paper
unjamming had caused thses to snap - not really a quality problem.
Thanks to some stiff wire and Duco(tm) cement, the printer is better
than new forcing retirement of my trusty $5 original DeskJet. :)
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