HP Forum Archive 11

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Capacitors Message #1 Posted by Howard on 26 Mar 2003, 8:52 a.m. Does anybody know what the replacement capacitors are for the HP67 card reader circuit? The old ones say - 4v 22k and the other says 4v 15k? Thank you.

Re: Capacitors Message #2 Posted by David Smith on 26 Mar 2003, 12:16 p.m., in response to message #1 by Howard If they are the silver tubular ones, I think they are 22uF and 15uF. The dipped tantalum versions are 22uF (yellow ones) and 3.3-6.8uF (small blue one that goes bad). Voltage ratings should be 10V or larger.

Re: Capacitors Message #3 Posted by David Smith on 26 Mar 2003, 6:03 p.m., in response to message #2 by David Smith I should also mention that these are tantalum capacitors. Most of them sold today are of a "dipped" construction that do not look like the cylindircal ones. The capacitors are also polarized (it matters which way they are installed... most HP products have a square pad around the "+" hole). The two 22uF caps are part of the read head circuitry. The 15uF one is the power filter.

Re: Capacitors Message #4 Posted by Malcolm Brooks on 26 Mar 2003, 8:19 p.m., in response to message #2 by David Smith To David, Can I have a bit of clarification on which is the capacitor that goes bad for card reading operations for the 67. In an old message by Tony Duell 12 June 2001 he clearly states the problem cap is a 47uF. Recent discussion says its a small blue 6.8uF cap. Is it two different capacitors? Where exactly are they located? Would these be the same on the 97 - I have both 67 and 97. Then there is the 22uF cap - does this not go bad? Are all tantalum caps the same for our purposes? Are all tantalum caps polarised? Any help much appreciated Thanks Malcolm

Re: Capacitors Message #5 Posted by David Smith on 27 Mar 2003, 6:16 p.m., in response to message #4 by Malcolm Brooks I think Tony's old post dropped the decimal point. The cap is technically a 4.7uF, but it's value is not particularly critical. I have used 3.3uF to 10uF. What can be critical is the size. If it is too big, the case won't close. I usually use 6.8uF because the local surplus store had a pile of them for cheap. The 22uF caps are basically in series with the heads. I have never seen one go bad. Almost every tantalum cap that you find is a polarized electrolytic. If they are installed backwards and powered up with a nice beefy power source they can explode like a small firecracker and throw pieces with uncanny accuracy straight for any uprotected eyeballs.

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