30 Nov
2016
30 Nov
'16
5:48 p.m.
You were correct, I was looking for the -12v in the wrong place. I did find
-12v on the anode of CR2. So all voltages are correct at the test points.
So the LCD shows nothing and the device does not seem to respond to keypad
presses.
The other symptom is that I can hear some feeble and irregular clicky
noises from the paper drive motor. So it isn't purely just that the display
failed.
thanks
M.
On Sun, Nov 27, 2016 at 1:02 PM, Brent Hilpert <hilpert at cs.ubc.ca> wrote:
(Getting back to this after a couple days..)
The board photos help although not detailed enough for certainty in
tracing.
I see the power supply test points on the photos and on the diagram 12-14
(page 12-28) of the manual.
Something to confirm: the -12V label is ambiguous in it's position on the
board, do you know for sure you measured the right spot for -12V?
It looks like it would be the nice solder button to the left of the minus
sign but from what I can discern it seems more likely to be the anode lead
of the diode (CR2), right above the "2" in the "-12V" label.
The diagram 12-14 indicates the test point as the cathode (banded lead) of
CR2, this is likely incorrect, if CR2 is the -12V rectifier the DC output
would be the anode end. It looks likes the draftsman just copied the
pattern for the +15V diode.
As you suggest, detailed assistance from a distance may be difficult, but
you might check the above and see where things stand.
I'm not all that far away (Victoria area) but far enough to nonetheless be
awkward for transport or trip.
On 2016-Nov-22, at 1:16 PM, Michael Newton wrote:
truncated.
I appreciate the guidance so far, thanks very
much.
I found another power supply/motor driver board ("analog board") of the
same part number, hooked it up to the plotter and tested it. The -12v test
point on the new board read zero, and the other voltages were present just
like the original board.
I don't suppose that proves anything, but at least now I have 2 power
supplies.
I don't have an electronics background other than hobby-level tinkering.
I
don't know how likely it is I'll be able to diagnose and fix this solely
on remote guidance, and in any case that seems like too much for me to ask.
If there is someone within driving distance of Seattle who could get
this thing
working I will pay them what their time and effort is worth (I'm
trying to avoid shipping this monster or buying anyone plane tickets).
thanks
M.
On Fri, Nov 18, 2016 at 3:17 PM, Michael Newton <
michael.newton at
gmail.com> wrote:
On Thu, Nov 17, 2016 at 12:10 AM, Brent Hilpert
<hilpert at cs.ubc.ca>
wrote:
On 2016-Nov-16, at 11:34 PM, Michael Newton
wrote:
ones
That's right, there is a -5v test point that
reads zero.
From the previous discussion, presumably you mean -12V.
Yes -12v, sorry
> Any guidance? Like if I need to pull parts off and test them, which might I
go for? I'm a caveman with electronics.
Looking at:
7595-7596_HardwareSupportManual_07595-90025_168pages_Feb90.pdf
from hpmuseum.net via the link you supplied, the document seems to be The document simply ends part way through the
schematics pages, and of
course the power supply schematic is missing.
(Aside, where did you find that document link? I
didn't find it ref'd on
the hpmuseum pages.)
It's linked from http://www.hpmuseum.net/collection_document.php -
search the
page for "DraftMaster"
The document does appear to be missing the full schematic of the analog
board. I
haven't been able to find them anywhere.
There is a minimal diagram for the power supply on page 5-4 (pdf.30),
which shows
the -12V supply as an independent (not part of the control
loop) secondary out of the switching supply. That's good as it limits the
likely problem region. There will be more components involved than shown
there, but the diode seen there on the -12V supply will lead to a filter
cap and possibly a 3-terminal linear regulator such as a 7912 or LM320-12,
or even a zener
regulator. There may be current limiting or
overvoltage circuitry
between there and the actual -12 output of the supply.
- identify the -12V componentry in the power supply.
- if there is a 3-terminal -12V regulator check for input to the
reg vs
output.
- confirm that it's not the load side
of the -12 causing the
problem.
- pic(s) of the power supply board might
help us identify the
area or get a better idea of what we're dealing with.
I took photos: https://goo.gl/photos/tRWV3ATTqx2R3eDz6