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HP-25 Capacitor Question
Message #1 Posted by Larry on 22 Sept 2001, 11:22 p.m.

On June 30, 2000 vrollinger posted that he was experiencing power on problems with his HP-27. Katie replied that the cause was probably the main filter capacitor in the power inverter. I am having similar problems with my HP-25. As I hold the circuit board in front of me with the large brown resistor on the right, where would I find this capacitor? Thanks.

      
Re: HP-25 Capacitor Question
Message #2 Posted by Vieira, Luiz C. (Brazil) on 23 Sept 2001, 10:36 a.m.,
in response to message #1 by Larry

Hello;

if yours is an HP25, it's a 22uF/16V elect. capacitor at the left side of the mboard, (+) pointed to the display assy. It is beside two transistors, normally from KEMET, SPRAGUE or others (it's all aluminum, transparent cover). If it is an HP25C, there are two tantalum capacitors and I do not know their values.

Hope it helps.

      
Re: HP-25 Capacitor Question
Message #3 Posted by Tony Duell (UK) on 23 Sept 2001, 1:54 p.m.,
in response to message #1 by Larry

If the HP25 is like the other Woodstocks, there are several filter capacitors. With the PCB in the position you describe, you should see a little transformer on the left 'strip'. Near it (and going up the left side towards the ROM0/anode driver chip) are several electrolytic capacitors (aluminium and tantalum bead). Check/change all of those.


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