+- HP Forums (https://www.hpmuseum.org/forum)
+-- Forum: HP Calculators (and very old HP Computers) (/forum-3.html)
+--- Forum: General Forum (/forum-4.html)
+--- Thread: How to clean sliding power switch on HP21 Woodstock (/thread-6849.html)
How to clean sliding power switch on HP21 Woodstock - jupiters_spot - 09-13-2016 06:12 PM
Hi - just rediscovered these forums after a decade of having calculators packed away and it has rejuvenated my interest.
I have an HP21 with a dirty power switch: most times when I slide the switch to "On" nothing happens until I jiggle or press on the switch, and then the calculator works fine. Sometimes I can slide it to "On" and it just works without jiggling. I think I need to clean the contacts, but I can't seem to find a way to access the switch.
I open the calculator and remove the boards, separating the keypad from the logic board. The keypad "half" of it contains the power switch, but the switch is sandwiched between the printed circuit board and the plastic fascia. Those two appear to be held together physically by the plastic posts from the fascia that protrude through the PCB and appear to have been melted over. It looks like it was not intended to be disassembled.
Does anyone have guidance on how to access the innards of the switch?
RE: How to clean sliding power switch on HP21 Woodstock - jupiters_spot - 09-13-2016 06:21 PM
Perhaps I posted prematurely. Upon further inspection, if you look from the display area towards the keyboard you can see the mechanics of the switch just beyond the edge of the PCB. It appears the switch is not enclosed, but rather that the slider and metal spring are held in place over the contacts on the PCB. Because that switch is adjacent to the PCB edge, I was able to spray some DeoxIT contact cleaner on the switch and slide it around a few times.
The switch now works reliably :-)
RE: How to clean sliding power switch on HP21 Woodstock - Dave Frederickson - 09-13-2016 07:17 PM
The switch should be lubricated in addition to being clean. The preferred lubricant is dielectric grease, like Loctite 37534.
Dave
RE: How to clean sliding power switch on HP21 Woodstock - jupiters_spot - 09-13-2016 07:28 PM
(09-13-2016 07:17 PM)Dave Frederickson Wrote: The switch should be lubricated in addition to being clean. The preferred lubricant is dielectric grease, like Loctite 37534.I have Permatex 22058 Dialetric Tune-Up Grease on hand, so I'll apply some of that. It appears to be the same sort of product, just from another vendor.
RE: How to clean sliding power switch on HP21 Woodstock - jupiters_spot - 09-13-2016 07:53 PM
(09-13-2016 07:17 PM)Dave Frederickson Wrote: The switch should be lubricated in addition to being clean. The preferred lubricant is dielectric grease, like Loctite 37534.
Dave
I applied dialectric grease and it's very happy.
I do wonder how others apply this grease. I also play with old watches, so I have some oilers that I use -- think of a handle with a fine-gauge wire sized to place one tiny drop of oil in a jewel cup. With that I was able to slide some grease in between the PCB and fascia, but it was tedious.
Here's an oiler:
![[Image: Gj1ZKHU.jpg]](http://i.imgur.com/Gj1ZKHU.jpg)
Dave - if you are able to apply grease to these switches without disassembling the keypad, how do you do it?
RE: How to clean sliding power switch on HP21 Woodstock - Dave Frederickson - 09-13-2016 08:33 PM
The switches on many other calculators and peripherals are accessable without disassembling the keypad. I haven't had to deal with a Woodstock, yet, but it looks like you've done a fine job.
Dave