HP Draftmaster RX pen plotter needs love

Philipp Pap philipp.pap at gmx.net
Tue May 9 13:29:35 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
OK, I just read in the service manual
„The power supple is a switching type dc supply incorporating a pulse-width modulator (PWM).“
but I don’t know the meaning on the drawing „+5V ref“ „vcc“ — POWER ON —„~RESET , HALT, RESET“
Could that mean that the problem could be in this „POWER ON“ block logic???

Thanks again!

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