HP Draftmaster RX pen plotter needs love

dwight dkelvey at hotmail.com
Tue May 9 15:27:36 CDT 2017

I would guess the lower voltages are generated from

a switcher off the 85 or 42 volt lines.

First check with an ohm meter in those lines to look for

a dead short.


From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Philipp Pap via cctalk <cctalk at classiccmp.org>
Sent: Tuesday, May 9, 2017 6:26:43 AM
To: michael.newton at gmail.com; cctalk at classiccmp.org
Subject: Re: HP Draftmaster RX pen plotter needs love

Hi Michael,
dear board

 Did you solve your power supply problem?

My Draftmaster I did work for 1 hour, I did even manage to do a demo plot.
 Then it died, right before my eyes the display got brighter and brighter and now - nothing when powering on, except a humming sound.
 I think that I’m responsible for the dead, as the plotter stood in an attic for 20 years, meanwhile power was raised from 220 to 230v (+-10%)
in Europe.
I realized that the input power can be adjusted between 220 and 240v at the power inlet of the plotter (on the top
there is a small stage for a screwdriver, then the cover opens and the rotating think can be taken out)!!

 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.
 Right now I am waiting for an esr-meter to test the capacitors,
any clue would be extremely helpful for me!

 With nice greetings Philipp
PS: tinkering with this masterpiece of engineering is fun, but now my back hurts, but it is worth it

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