HP-25 Capacitor Question


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.



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.


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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