HP Forum Archive 20

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HP-35: once working, now only one dim segment on display Message #1 Posted by elmwood on 31 Aug 2011, 2:08 p.m. Greetings all! I rescued a old HP-35 calculator not too long ago. ($1!) It worked perfectly, but I still disassembled and carefully cleaned the internals, with no problems. Today, I got a new aftermarket 2000mAh rechargeable battery pack, to replace the original leaked and dead battery pack. I installed the battery, plugged in the HP-35, and all was well. I then turned off the calculator. A few minutes later, I turned the calculator back on. There's no familiar "0" in the first LED; instead, there will be one lone, very dim segment displayed in the fourth LED from the left. The displayed segment changes when I turn the calculator on and off. Occasionally, it will display two very dim decimal points in the fourth and fifth LED. It doesn't matter whether I use only the battery, the power supply without the battery, or both together - the result is the same. Any thoughts?

Re: HP-35: once working, now only one dim segment on display Message #2 Posted by elmwood on 31 Aug 2011, 10:16 p.m., in response to message #1 by elmwood Bump. Anyone? Or are you all just waiting for it to come up for sale on eBay for parts ...

Re: HP-35: once working, now only one dim segment on display Message #3 Posted by Michael de Estrada on 31 Aug 2011, 10:55 p.m., in response to message #2 by elmwood Maybe one of the truly expert members here will chime in. We're not ignoring you, just don't have a good idea what specifically it could be. Normally when displays stop working properly, some electronic component has gone bad in which case you won't be able to repair it unless you are able to get your hands on a donor calculator. Since you only paid $1 for it, just put it in a closet or toss it.

Re: HP-35: once working, now only one dim segment on display Message #4 Posted by Peter Murphy (Livermore) on 1 Sept 2011, 1:52 a.m., in response to message #3 by Michael de Estrada An idea: ask Randy Sloyer at FixThatCalc.com if he could use your 35 for spare parts. He's done good work for me, at fair prices, so I've been happy to have found some old, inoperative calcs to send him.

Re: HP-35: once working, now only one dim segment on display Message #5 Posted by Joel Setton (France) on 1 Sept 2011, 2:34 a.m., in response to message #1 by elmwood I know this may sound trivial, but are you sure the new battery pack has any charge in it?And did you try running the calculator on a charger? Joel Setton

Re: HP-35: once working, now only one dim segment on display Message #6 Posted by Randy on 1 Sept 2011, 11:17 a.m., in response to message #1 by elmwood Perhaps you received a bad battery? Low voltage can cause the symptom you see. Anything is possible, I've seen both bad cells and reversed cells in after-market packs. As the 35 will work safely from the charger alone, remove the battery and try with just the ac adapter. If no joy, check the output of the charger. The center pin is common, one side is regulated ~4.5 volts dc and the other side is a 55 ma constant current source that charges the battery that when open circuit, should measure approximately 16 volts dc. A schematic is available in the archives: Classic charger schematic

Re: HP-35: once working, now only one dim segment on display Message #7 Posted by Dave Shaffer (Arizona) on 1 Sept 2011, 1:17 p.m., in response to message #6 by Randy I think I have an extra '35 charger, which I would be glad to donate to a worthy machine. (It might even have a NASA sticker on it!!)

Re: HP-35: once working, now only one dim segment on display Message #8 Posted by Andrew Treloar on 3 Sept 2011, 1:50 a.m., in response to message #7 by Dave Shaffer (Arizona) I'm trying to get my father's old HP35 working. The power supply is broken (the transformer has become disconnected from the circuit board - all four traces are broken) and I can't find anywhere to buy a replacement. Is your offer of a charger still open?

Re: HP-35: once working, now only one dim segment on display Message #9 Posted by Dave Shaffer (Arizona) on 3 Sept 2011, 11:28 a.m., in response to message #8 by Andrew Treloar Andrew, Yeah - my offer is still open, but now I need to find my other (my original!) charger first. Let's go off-forum to continue (shaffer (at) alumni.caltech.edu ). As I was looking, I came across a 82041A charger (for Woodstocks, I guess). Somebody has one listed on TAS for $120! Is that reasonable?

Re: HP-35: once working, now only one dim segment on display Message #10 Posted by Michael de Estrada on 3 Sept 2011, 11:56 a.m., in response to message #9 by Dave Shaffer (Arizona) Quote: As I was looking, I came across a 82041A charger (for Woodstocks, I guess). Somebody has one listed on TAS for $120! Is that reasonable? That's beyond absurd.

Re: HP-35: once working, now only one dim segment on display Message #11 Posted by Thomas Radtke on 1 Sept 2011, 1:51 p.m., in response to message #1 by elmwood The wires are often broken on the charger near the plug. Try to move it slightly and see if it helps.

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