- Vintage Hp Hewlett-Packard 25 Calculator with case and charger - 6 Updates
- SOLVED! GFCI tripping problem - 1 Update
| John-Del <ohger1s@gmail.com>: Aug 09 12:34PM -0700 On Thursday, August 9, 2018 at 10:53:23 AM UTC-4, Jeff Liebermann wrote: The > political discussion continues until someone mentions Trump, where it > degenerates into one-line comments of little intelligence and less > importance. Yeah, those Trump Bashers are nothing if not persistent. > off, documentation written in readable English, mostly bug free > firmware, batteries that aren't intentionally overcharged, and wall > warts that don't blow up. I have a question for you Jeff concerning the HP line. I have an HP34C that I bought new back around 1980 or so to replace my stolen TI SR-51A. It had always been a little flakey but a quick thump brought it back around. A few years later I decided to have a look inside when it required more physical persuasion to behave. I took a picture of the front keys in case they decided to jump out and get mixed up (they did), but I was surprised to find the half dozen ICs *not* soldered down to the flexible circuit board. They maintain connection by the foam cushion beneath the flex circuit that maintains pressure between the flex circuit and the ICs. I removed each IC, cleaned all the pins and the flex circuit lands, put a tiny bit of dielectric grease on each IC pin, and reassembled. It behaved itself for quite some time. Right now it's been in storage for many years but every once in a while I wonder if the correct solution would be to tack solder them down. I'm sure the foam pad looses a bit of rebound over the years. What do you do when you run across flakey IC contacts in an HP? |
| John-Del <ohger1s@gmail.com>: Aug 09 01:06PM -0700 On Thursday, August 9, 2018 at 3:34:57 PM UTC-4, John-Del wrote: I'm sure the foam pad *looses a bit of rebound over the years. *Loses... |
| "pfjw@aol.com" <peterwieck33@gmail.com>: Aug 09 01:09PM -0700 On Thursday, August 9, 2018 at 4:06:30 PM UTC-4, John-Del wrote: > On Thursday, August 9, 2018 at 3:34:57 PM UTC-4, John-Del wrote: > I'm sure the foam pad *looses a bit of rebound over the years. > *Loses... Oh, I dunno - there is a certain elegance to "loosing" a rebound. Peter Wieck Melrose Park, PA |
| John-Del <ohger1s@gmail.com>: Aug 09 07:18PM -0700 > Oh, I dunno - there is a certain elegance to "loosing" a rebound. > Peter Wieck > Melrose Park, PA LOL. It was *you* Peter that I had in mind when I made that correction!!! I figured if anyone would catch that goof and make me pay for it it would be you. |
| Jeff Liebermann <jeffl@cruzio.com>: Aug 09 09:23PM -0700 On Thu, 9 Aug 2018 12:34:54 -0700 (PDT), John-Del <ohger1s@gmail.com> wrote: >I took a picture of the front keys in case they decided to jump out >and get mixed up (they did), but I was surprised to find the half >dozen ICs *not* soldered down to the flexible circuit board. Yep. It relies on the pressure provided by a foam pad to make the connection. Bad bad bad idea: <http://www.hpmuseum.org/hp34.htm> >solder them down. I'm sure the foam pad looses a bit of rebound >over the years. >What do you do when you run across flakey IC contacts in an HP? If the foam pad was in good shape (springy), I would add a 2nd foam pad to give it more pressure. This added pad is rather thin. I should repalce both, but can't find a suitable sheet of foam. I now have access to a laser cutter, so I might be able to cut some foam that will work. I think ordinary soldering is a bad idea and have never tried it. However, if you do decide to try it, I suggest you use low temperature 180C bismuth solder paste, liquid flux, and a temperature controlled toaster oven. <https://www.ebay.com/sch/i.html?_nkw=low+temperature+bismuth+solder+paste> Something like this: <https://www.youtube.com/watch?v=cClPqIJwhLs> On the toaster oven, this is how I do BGA reflow on HP JetDirect cards, which use the same bismuth solder paste: <http://www.learnbydestroying.com/jeffl/pics/repair/BGA%20reflow/index.html> -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
| John-Del <ohger1s@gmail.com>: Aug 10 04:55AM -0700 On Friday, August 10, 2018 at 12:23:46 AM UTC-4, Jeff Liebermann wrote: > 150 Felker St #D http://www.LearnByDestroying.com > Santa Cruz CA 95060 http://802.11junk.com > Skype: JeffLiebermann AE6KS 831-336-2558 I'm going to dig it out of storage, charge the battery, and see how it behaves. If it behaves, I'll leave it as is. I didn't attempt a resolder back then because I didn't want to modify it and wasn't sure of the flex circuit's response to heat. In later years, I've seen flex circuits (I think they're Kapton) that take soldering heat just fine. I do keep solder paste in stock because I do a lot of smd IC replacement, and mostly use a hot-air station to keep the heat localized. Thanks for the info. |
| bruce2bowser@gmail.com: Aug 09 06:46PM -0700 > All, repeat, all neutrals are shared - at the panel. As are load-side live wires (in Europe and Asia, I last heard). |
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