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
