I seem to have a plotter-based theme going here today...
Snagged an HP 7240A (this is the RS-232 version of the 7245A) plotter
today, it's in working condition. A really cool design -- a combination
Nice! I have a 7245A (HPIB of course) and I think it's a very interesting
design.
As you probably know the printhead has 13 elements. 12 of them, in a
staggered diagonal pattern are used for printign test (either
horizontally or vertically). The 13th is a 'pen' used for vector
plotting. The power to that one is controlleed so that all lines come out
in the same intensity.
Howe similar is it to the 7245? I always throught it silly that in the
7245A (at least) they didn't route the +/-12V rails to the interface PCB
connector. The interface PCB slotsin from the rear, and having 12V on
that connector ould have made making an RS232 board a lot easier. Perhaps
the 7240 remidies this.
Does it have thr interesign internal self-tests? I had great fun settign
up the motro drivrrs in mine...
I assume you'ge got inside it. The casing screwas are not obvious. From
waht I remmeber there are 4 scres on the back holding the mains rectifier
unit to the case. Take out the top 2 only. Then remvoe the front
nameplate bush pushjign on the 2 pins inside and remvoe the 2 screws
under it. Then the case comes off.
Do not take the mechanism apart unless you have the special tools to
reallign it. I made up a set, but it's not trivial...
plotter/printer using a thermal print head. My
understanding is that the
special tractor-feed thermal paper for this thing is basically
impossible to find. Anyone out there found a reasonable substitute?
The main problem is those holes. And that one hole per page (at least in
the roll paper) is elongaged to give a top-of-form posiiton. The
Australian HP museum suggests stickign sprokceted eges to fax paper, I
doubt theyv'e ever tried this :-)
Mine came with maybe 1/4 of a roll left in it, and I
guess after that's
gone I'll probably never get to use it again :).
I was lucky enough to get half a dozen rolls with my 7245A, but I have
no idea what I will do when they run out .
Here are a few notes on the 7245A...
PSU Fan Dismantling
-------------------
Dismantle PSU. Disconnect mains input harness from 'line' switch (push-on
terminals). Remove fan and harness from PSU chassis.
Remove cable clip on fan housing. Undo 2 slot-head screws (under label).
Feed cable through housing and remove motor/blade assembly. Recover
thrust pad (inside housing.
Rmmove circlip from end of spindle. Lift off waskers. Remove blade/rotor
from stator.
Lubricate bearings with light machine oil when reassembling
X Drive Fan Dismantling
-----------------------
Remove fan from X drive chassis (3 screws). Remove adapter from fan (one
further screw).
Remove 4 crosshead screws on fan motor plate. Lift motor assembly out of
housing. Remove 2 slothead screws (under label) and take off plate.
Remove circlip from spindle end WITH CARE, it is spring loaded. Take off
washer, ball race, 'tophat' spacer, spring, second 'tophat' spacer. Lift
out stator and remove second ball race and spacer from spindle.
X Drive Chassis
---------------
Anticlockwise rotation of motor -> Carriage moves to right
To lock motor, apply 5V to one motor winding (e.g. between red and yellow
wires at motor connnector)
Fit to LH side plate :
Microswitch harness (2 microswitches)
Paper roll clip
Y drive clip
Y drive stop (shorter 'tail')
Tensioner assembly
Fit to RH side plate :
Paper roll clip
Y drive clip
Y drive stop (longer 'tail')
Bail spring (loop towards rear of machine)
2 idlers
Motor mounting bracket
Assemble chassis. Fit motor (wires on left side, nuts on front side)
Fit pulley, hole at top. Lock motor (see above).
Fit cable :
LH cable (long end). 3 turns anticlockwise from hole, towards back.
RH cable (short end) : 1+3/4 turns clockwise from hole, towards front.
Y drive special tools
---------------------
1) 3 spacers, Each 30mm long, made from 1/2" brass rod, 3.5mm hole drilled
centrally (along axis). Length is reasonably critical. These are used in
place of the plastic motor mount when using the platten-movement tool and
checking the motor coupling
2) Platten-movement tool. Brass block, 5/8" square by 3" long. Drill
centrally 5mm, and tap M6 (1). Drill 3.5mm holes 1+5/16" either side of
this (approximately 316" from ends of bar). All holes to be aligned along
center of bar, and drilled perpendicualr to the face :
Top View:
Centre Line
|
+----------------------------+ ----
| o * o | 5/8"
+----------------------------+ ----
| | | | |
| | <1+5/16> | <1+5/16> | |
| | | |
| <----------3-------------> |
Mill away ends of bar to reduce thickness to aproximately 1/8" (thickness
of motor flange) for about 1/2"
SIde view:
+------------------------+ ----------
| | 1/2
| |
+-----+ + ----+ ----------
| | 1/8
+ -----------------------------------+ ----------
| | | |
| | | |
|<1/2>| <-------2------------> |<1/2>|
The central hole is fitted with an M6 (1) bolt. Either a stnadard
commercial one, or make a both from 1/4" or 5/16" brass rod, turned down
to 6 mm and threaded with a die for a length of 50 mm. Knurl the 'head'
end to give a suitable grip and part off.
In use, this tool is fitted in place of the stepper motor, using 2 of the
spacers mentioned above. The M6 screw presses on the end of the platten
spindle. With the platten fixing screws hand-tight, the M6 screw is used
to postion the platten to align the LH sprockets.
(1) THis thrad is not critical, although obviously the hole and bolt must
be the same thread. M6 is 1mm pitch. 0BA, or 1/4-28 UNF would be fine too.
3) A courved straightedge. This is fitted round the platten, in contact
with the teeth on the LH sprockt. It is then used to line up those teeth
with the ones on the LH drum sproket.
Turn a brass cylinder 1.27" (32,3mm) diameter by 5/8" thick
(approximately). Drill a 3.5mm hole along the axis, tap M4. Drill a 2.5mm
hole radially, 1/4" from one face, tap M3.
Drill a 4mm hole in a 6" (approx) flat metal square (e.g. 1/8" thick
aluminium), aporximately 1.5" from the edges. Screw the cylinder there
with an M4 screww, radial hole closer to the plate.
The actaul straightedge is made from brass strip, 1/2" wide. Drill a 4mm
hole on the centre line close to one end, fix to the cylinder with an M3
screw and washer. Ensure the strip contacts the plate along its full
length. Bend the strip round the cylinder by hand for about 1/2 turn,
keeping it in contact with the plate. Remove from the cylinder, continue
forming by hand so as to fit closely round it.
Y Drive Assembly
----------------
Assemble the following 6 subassemblies first.
1) Belt cover : Fit the belt spring leaf (2 screws/nuts/washers)
2) Paper clamp : Assemble the tension arms to the side rails, fit the
springs. Assemble the front roller (presses against drum when machine is
asembled), screw side rails to this. Fit the white plastic guide roller
to the tension arms
3) Paper sensor top cover. Assmeble the magnet, metal return plate, 2
spacers to this plate with 2 screws, washers, and nuts.
4) Paper sensors : Fit the U-shaped brackets to the cross rail. The
easiest way to do this is to fit the spring to the cross rail, using a thin
rod (e.g. a small crosspoint or Torx srewdriver inserted through the hole
on the bottom of this rail to giude it in place. Then fit the bracket to
the rail alongside the sping ( top upringht (tapped hole) inside the
rail), pull out the rodn amd use a small screwdriver to compress the
spring a little and slide the bracket in place. Use the rod to align the
spring and the holes in the rail and U-bracket. Fit the special adjusting
screw from the bottom, screw into the tapped hole in the U-bracket. Fit
the reflective optoswitches to the sensor PCBs, fit these to the
U-brackets (PCB away from the bracket), fit the allen-head screws and
tighten (Sensor pin side against the 'bumps' on the U bracket). Fit the
cross rail to the left side plate (cable form under the rail), fit the
fixing screw finger-tight.
5) Platten : Fit an E-circlip into the grouve on the platten spindle (this
is the one with one end turned down). Fit a plain (not flanged) ball race
inside the platten at each end. WIth the platten mounting face away from
you and the flat (prinhead surface) towards the top, slide in the spindle
from the RHS, fit a samll sprocket on the LH end, fit a
clamp and
tighten. Slide the other small sproket onto the RH end of the spindle,
fit the coupling/belt sprocket (pin to go through hole in paper
sprocket), fit clamp. Place assembly on a flat surface and alighn the
pins on the 2 paper sprockets. Tighten the clamp at the RH side. Fit the
mouting rail to the platten with 3 allen screws, finger tight.
6) Drum : Fit an E circlip into the grouve nearest the end of the drum
spindle. Slide a large paper sprocket onto thi from the long end of the
spinddle (clamp end to be towarfs the long end, fit a clamp. Slide the
sprocket hard against the E-clrclip, tighten the clamp. Fit the drum
tube, the metal drum onto the spindle, fit a clamp inside the latter so
that the screw can be accessed via the hole in the metal drum. Fit the
other large sprocket, engaging the pin on the metal drum with its hole.
Alight the teeth on the paper sprokects on a flat surface as before and
tighten the clamp. Fit an E-circlip into the remaing groove on the drum
spindle. Slide a flanged ball race onto each end of the drum spridle,
flanges towards the drum.
Assembling the Y drive : Fit the platten to the left side plate, motor
coupling/sprocket to the right. Fit and tighten 2 screws. Fit the drum
into the left side plate, short end of the spindle to the left. Fit the
right side plate, motor harness loop under the paper sensor cross rail.
Screw in the the 3 screws that hold the the RH side plate in place. Leave
the one in the paper sensor rail finger-tight, note that the top screw on
the platten mouting on this slde is the long one and fitted with a spacer
under the head (to keep the motor harness away from moving parts.
Fit the hase plate under the paper sesnor, the paper senosr harness and
notor harness fit into the slot on the cross rail. Screw to the cross rail
with 1 screws and to the lugs on the side plates with 4 scress and
hexagonal spacers. Tighten the 2 screws holding the sensor cross rail to
the side plates.
Fit the platten movement tool to the stepper motor mouting holes with 2
motor mouting screws and 2 of the spacers made earlier. Slide the platten
all the way to the right and screw in the the bolt on the tool until it
just touches the end of the shaft. Fit the curved straightedge tool round
the platnen, againsts the teeth of the LH paper sprocket. Screw in the
bolt of the movement tool until the straightedge contacts the teeth of
the LH drum sprocket. Tighten the 3 allen screws holding the platten to
the mouting rail (a ball-ended tool is useful here), remvoe the special
tools.
Fit the toothed belt to the platten motor coupling sproket. Fit the
sproket to the drum spindle. Fit the tensioner sleeve to the tensioner,
fit this to the side plate with 1 screw. Turn it to tension the belt,
tighten the screw. Fit the clamp to the drum sprocket, leave untightened.
Run a length of plotter paper over the sprockets on the drum and platten.
Routate the latter so that all teeth enter holes on the paper and tighten
the clamp on the drum sprocket.
Fit the motor coupling to the motor and fit the clamp. Fit the cross
piece to the platten coupling, fit the motor to the side plate with the 3
screws and the spacers made earlier. Tighten the clamp on the motor
coupling. Check everything turns freely. Remove the motor and the
spacers. Fit the motor to the motor mount (1 screw and nut). The motor
wires are routed down the side of the motor, through a slot in the mount.
Fit this assembly to the mechanism, checking that the cross piece is
correctly engaged and that the cable is routed above the long screw on
the platten mouning. Fit the 3 motor screws and tighten. Plug the motor
cable into the motor harness and fit the connectors and cables into the
grouve on the side plate.
Fit the paper clamp assembly, 1 screw and large washer on one side, 1
screw and bush on the other. FIt the belt cover (2 screws), check this
latches the paper clamp
Fit the top cover on the paper sensor (5 screws)
---------------------------
Extraced from the 7245A manuals...
-------
I/O PCB
-------
Thermal Head Vector Resistor Adjustment
---------------------------------------
1) Unplug Printhead !
2) Conenct DVM (15V range) between TP1 (I/O PCB) and analogue common
3) Connect TP4 to analogue common
4) Adjust Bias (R91/RV3) to get 7.88V to 7.96V
5) Short TP2 to TP3
6) Adjust Gain (R90/RV2) to get 13.03V to 13.17V.
7) Remove jumpers
Thermal Head Character Resistor Adjustment
------------------------------------------
1) Ensure head unplugged
2) Connect DVM (15V range) between TP7 (I/O PCB) and analogue common
3) Adjust R89 (RV1) for 13.37V to 13.63V
4) Remove leads, connect head
------------
MOTOR DRIVER
------------
DAC Offset/Gain
---------------
1) Turn off X and Y motors
2) Turn 3rd Harmonic pots R89 (X) and R88 (Y) fully ccw
3) DIP switch 1,4 open; 2,3 closed
4) DVM (10V) betwen TP2 and analogue common
5) Reset
6) Adjust DAC offest (R87( for -4.48V to -4.52V
7) DIP switch 1,3,4 open; 2 closed
8) Adjust DAC Gain (R86) fro +4.48V to +4.52V
9) Repeat 3-8 to minimise interaction effects.
X 3rd harmonic preliminary
--------------------------
1) DIP Swtich 1,4 open; 2,3 closed
2) Adjust R89 (X 3rd harmonic) for -5.98V to -6.02V)
Y 3rd harmonic preliminary
--------------------------
1) DMM between TP9 and analogue common
2) Adjust R88 (Y 3rd harmonic) for -5.98 to -6.02V
3) DIP swtich 1 cloced; 2,3,4 open
Turn on X motor
X 3rd harmonic adjustment
-------------------------
1) Postion carriage within 1cm of LH side
2) Postion paper with 1 full page out, perforation ~5cm above window
3) Select test 32(8), STEP
4) Adjust X 3rd harmonic pot (R89) for minimum vibration with finger on
carriage
5) Press STEP until carriage stops
Driver X amplifier gain
-----------------------
1) Select test 31(8), STEP
2) Adjust X gain XG (R91) for minimum vibration
3) Press STEP until carriage stops
Driver X amplifier offsets
--------------------------
1) Select test 30(8), STEP
2) Set X offset XO2 (R92) to mid position
3) Adjust X01 (R90) for minimum vibration
4) Adjust X02 (R92) for minimum vibration
5) Press STEP until carriage stops
Turn off X motor, turn on Y
Y 3rd harmonic adjustment
-------------------------
1) Selct test 36(8), STEP
2) Adjust Y 3rd pot (R88) for minimum vibration/noise
3) Press STEP until paper stops
Driver amplifier Y gain
------------------------
1) Select test 35(8), STEP
2) Adjust YG (R94) for minimum vibration/noise
3) Press STEP until paper stops
Driver amplifier Y offset
-------------------------
1) Select test 34(8), STEP
2) Set YO2 (R95) to mid position
3) Adjust YO1 (R93) for minimum vibration/noise
4) Adjust YO2 (R95) for minimum vibration/noise
5) Press STEP until paper stops
Turn on both motors
Summary
-------
Seq Test X Motor Y Motor Adjust
1 32(8) On Off X 3rd
2 31(8) On Off XG
3 30(8) On Off XO2 mid, adj XO1; adj XO2
4 36(8) Off On Y 3rd
5 35(8) Off On YG
6 34(8) Off On YO" mid, adj YO1; adj YO2
Test 37(8) plots lines from all 6 vector tests
Test 27(8) prints characters.
-tony