Tech Forum
damaging the deflection circuits.
Jason Neill
Jersey City, NJ
[#1053 - January 2005]
I have acquired an HP 7580B
plotter that is mechanically sound.
When I turn it on, E02 is displayed
after a self-test. The operator
manual says it’s a microprocessor
error/ROM checksum error. When I
plot a drawing, it plots to one side
and only half of the drawing is on
the page.
Alex Malachowski
Via Internet
F
o
r
E
l
e
c
t
r
o
n
i
c
s
#1 Since the plotter is functioning,
it seems likely that the E02 is from
the EEPROM that is used to calibrate
the unit, although I don't have the
manuals to check that. EEPROM
technology was quite new when the
7586B was designed, the part used
was quite unreliable, and the part is
probably unobtainable. If the part
were replaced, the 7586B can be
calibrated, but the process is tedious.
This means that the unit can be
used to make drawings, where high
accuracy is not a concern, but is
probably not useful for PCB layouts or
mask making.
NUTS & VOLTS
E
v
e
r
y
t
h
i
n
g
The offset plotting is probably an
HPGL compatibility issue. The HPGL
language was revised after the 7586
was made, becoming HPGL/2, and
most newer drivers are made for
plotting to HPGL/2 devices. If you can
capture and edit the plot file, it should
be possible to center the plot by
changing a few of the HPGL
commands in the header, such as
scaling (SC), input corners (IP), and
input window (IW). The default
coordinate system of the 7586 had
the origin in the center of the page,
with plotter units of .025 mm, where
the pen moves in the Y axis and the
paper moves in the X axis.
Charles Keith
Poway, CA
#2 Congratulations on getting as
far along with troubleshooting your
plotter as you have. You say that you
94
have a ROM error. I saw a similar case
back in the early 80s at a large
aerospace company. An experienced
microcomputer technician returned
an old microcomputer to service by
removing the EPROMs, reading them
into a programmer, and burning a
new set for reinstallation.
Why would this work? The
EPROMs had deteriorated to the
extent that at least one bit in one word
could not be read at the normal
execution speed of the
microprocessor. However, the
EPROMs could still be read by the
slower process used by the
programmer to read in a good copy.
Once a new copy was made in new
devices, the code could be read and
executed at the normal speed of the
microprocessor.
Open the plotter to determine
what type of EPROMS you have. Look
for some 24-pin, 0.6-inch-wide
socketed devices with stick-on labels
affixed to the quartz windows. Expect
to find two to four EPROMs. Look for
part numbers such as 2716, 2732.
The Jameco catalog still lists devices
as old as 2708, though I have not
seen any that old in a plotter. Any
dash numbers after your part number
indicate the speed grade. Buy
replacement devices of the same
speed or faster, that is, a smaller dash
number.
You will need access to an
EPROM programmer, or someone
who has access. The device that you
propose to program needs to be on
the list of programmable devices for
that programmer. Per instructions for
the programmer, read in an original
device and program a new device.
Repeat this for all EPROMs. Install the
new set of EPROMS in the plotter.
Good luck as you power up the
plotter.
Dennis Crunkilton
Abilene,TX
[#1052 - January 2005]
I am looking for a simple on/off
switch that can be triggered by
electrodes placed on the skin. It
needs to have a sensitivity
adjustment. I would also like to
have it opto-isolated for safety. Any
suggestions or places I can look?
Chris Tauscher
Via Internet
Take a look at the following
books that contain all the information
needed:
Introduction to Biomedical
Equipment Technology
Joseph Carr, John M. Brown
Prentice Hall
ISBN: 0138494312
This is a textbook aimed towards
the design and repair of medical
equipment, but covers all the basics.
A very good quality of this book is
that it contains lots of practical
information and circuits.
The author, Joseph Carr, had a
prolific life of writing and researching
a lot of topics related to electronics.
Another good book, maybe a bit
more theoretical is:
Medical Instrumentation
John G. Webster
Houghton Mifflin Company
These books should be available
in the local library or that of a nearby
community college or university.
Albert Lozano
Edwardsville, PA
[#2051 -February 2005]
I’m trying to find service
information or help for a BSR
MCD8090 AM/FM Stereo Receiver.
This unit was called a "Thunder
Thrower" and was purchased from
DAK Industries. The FM section is
not working.
Mike Uschak
Loyalhanna, PA
Most stereo receivers are laid out
in a very logical manner. You can
usually trace the signal path from
input to output.
Start at the FM antenna terminals
and trace the wiring back through the
front-end (probably a sealed module
on this receiver) and through the IF
stages. The IF stages may only be a
single chip. A little careful probing
along the signal path with an
APRIL 2005
