HP Draftmaster RX pen plotter needs love

Philipp Pap philipp.pap at gmx.net
Tue May 9 13:23:05 CDT 2017

> Am 09.05.2017 um 18:10 schrieb Jon Elson <elson at pico-systems.com>:
> On 05/09/2017 08:26 AM, Philipp Pap via cctalk wrote:
>>  Anyhow, now I have 41 and 83 Volts at the 42 and 85V test points,
>>  but always 0 Volts at the +5,-12,+12,+15V test points.
>>  The fuses are good and the secondary transformer seems good as well.
> Does this have a switching power supply for the logic (5, 12, 15V) or is it a rectifier/filter/regulator off the transformer?
> If rectifier/filter/regulator, it seems odd that FOUR voltages would quit at once.  So, I'm guessing it might have a switching supply for those voltages.  It sounds like the regulation circuit failed (display got brighter) and then a crowbar circuit tripped to shut it down.  Unless you are pretty skilled, switchers can be a bit hard to troubleshoot.  It might be easier to get a supply with the needed voltages and just patch it in.
> Jon


Could you please have a quick look at the photos here https://goo.gl/photos/m5qW1bz8kSujfK7J8 as I’m way under your skill level.
Does this look like rectifier/filter/regulator or a switching supply?
A complete schematic would make things simpler.

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