HP Draftmaster RX pen plotter needs love

Jon Elson elson at pico-systems.com
Tue May 9 11:10:18 CDT 2017

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 
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.


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