If you have an oscilloscope or logic analyser see if you have a clock signal at the main CPU. If you do, see if your EPROMs are being accessed. If not you may have a clock issue, a bad CPU or the CPU reset stuck low.
David Collins (Sent from out of office) > On 1 Dec. 2016, at 12:48 pm, Michael Newton <michael.new...@gmail.com> wrote: > > 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 <hilp...@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: >>> 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.new...@gmail.com> wrote: >>> On Thu, Nov 17, 2016 at 12:10 AM, Brent Hilpert <hilp...@cs.ubc.ca> >> wrote: >>>> On 2016-Nov-16, at 11:34 PM, Michael Newton wrote: >>>> >>>> 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 >> ones >>>> 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 >> truncated. >>> 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 >> >>