HP-21 Disassembly Help...

[Jeff_Kearns]

I have a sticky '1' key on my HP-21, and it has gotten to the point where it needs to be cleaned/repaired. So off I go...

As I have all but given up on getting a copy of Geoff's manual to do this properly (any time soon), I thought i would tackle it by myself following the ever-so-concise instructions here to separate the keyboard from the case.

It is not so easy and although the keyboard does 'pivot' somewhat, it not enough to access the keys and I fear I will break it if I don't do this properly. Any advice on how to do this right? It is a great little calc and goes well with a custom wooden stand that sits on my desk.

Jeff

[rprosperi]

(03-26-2016 07:06 PM)Jeff_Kearns Wrote:  I have a sticky '1' key on my HP-21, and it has gotten to the point where it needs to be cleaned/repaired. So off I go...

I have the identical problem, same '1' key, also on a '21. I've peeked at opening it in the past, but feared to tread there, so I'll watch replies to your post...

[Jeff_Kearns]

Bob - In the meantime, I will try to avoid the sickening sound of cracking plastic/circuitry!

[Geoff Quickfall]

Stop!

Firstly, let me get home. Do not remove the heat stakes on The Woodstock.


There are less intrusive fixes first.

Geoff

[Jeff_Kearns]

(03-26-2016 09:28 PM)Geoff Quickfall Wrote:  Stop!

I stopped! You are just the guy I was waiting for... Standing by.

Jeff

[Katie Wasserman]

(03-26-2016 11:07 PM)Jeff_Kearns Wrote:  

(03-26-2016 09:28 PM)Geoff Quickfall Wrote:  Stop!

I stopped! You are just the guy I was waiting for... Standing by.

Jeff

I'm not sure what Geoff has up his sleeve, but I've had some success with using some very thin stranded wire, spread out and inserted in the tiny holes in the PCB. I put a drop of 99% isopropanol into the hole first then insert the wire bent at at angle and use this to brush around on unseen side to the PCB. You an try Deoxit too.

[Geoff Quickfall]

That's a good one Katie, but not all Woodstocks have the holes! My five 21 boards do not have the holes on the reverse side of the keyboard under the domes. My 25, 25c, 27, 29 all have those pores we are familiar with. For some reason the 21 does not.

No holes in 21:



Holes in various other HP family boards:
Red arrows pores, yellow arrows snap domes




I was going to suggest the wire trick but only after drilling a tiny hole underneath the offending dome on under side of the keyboard. I want to get home to try it before telling Jeff to attempt it.

Jeff, if you are willing to attempt a drill before I get home, I suggest getting the finest bit you can get, 1/32nd, 1/64th. If you have a Dremmel stand and are able to set the drill depth then that is the best option. You just want to drill the PCA board and not any deeper. If no stand I would take the bit in a pin vice and drill with your thumb and fore finger, only a drill bit then just the drill bit, thumb and forefinger. Looking at the PCA board you can see the black rivets. You can also see round contact traces residing directly under the snap domes on the underside of the keyboard PCA. I would drill to one side of the round snap dome contact trace that you can see.

I use deoxit red which contains a solvent which is safe on all plastics and a deoxidant, then as Katie mentions, introduce a fine bent wire into the hole and twirl it cleaning any oxidation.


Hope this helps.

On a different note in lieu of the fact that I won't be home on the 1st of next month. Just finished a chapter allowing the creation of this:

[Jeff_Kearns]

(03-27-2016 04:36 PM)Geoff Quickfall Wrote:  I want to get home to try it before telling Jeff to attempt it.

Geoff,

I can wait... PM me when you get home please. Thanks!

Jeff

[Dave Frederickson]

(03-27-2016 04:36 PM)Geoff Quickfall Wrote:  I suggest getting the finest bit you can get, 1/32nd, 1/64th. If you have a Dremmel stand and are able to set the drill depth then that is the best option.

Any concern about debris from the drill getting under the dome? If smaller is better then a size 80 (0.0135 inches) drill in a pinvise could be a consideration.

(03-27-2016 04:36 PM)Geoff Quickfall Wrote:  I use deoxit red which contains a solvent which is safe on all plastics and a deoxidant, then as Katie mentions, introduce a fine bent wire into the hole and twirl it cleaning any oxidation.

By "red" you're referring to the D100L, as opposed to the "Gold" G100L, formulation?

Dave

[Katie Wasserman]

(03-27-2016 04:36 PM)Geoff Quickfall Wrote:  On a different note in lieu of the fact that I won't be home on the 1st of next month. Just finished a chapter allowing the creation of this:

I can't wait to read that chapter, especially the part about the micro-miniturized cold fusion reactor that you've come up with to power it!

Also..... I never realized that the HP-21 doesn't have holes in the PCB, I guess I never had to clean the keys on one of them.

[PANAMATIK]

(03-30-2016 12:54 AM)Katie Wasserman Wrote:  Also..... I never realized that the HP-21 doesn't have holes in the PCB, I guess I never had to clean the keys on one of them.

Also many (or all, I don't know) HP-29 keyboards doesn't have holes in the PCB.

And I hope the fusion reactor doesn't have holes either!

Bernhard

[Geoff Quickfall]

I will now check my 29s!

Another shot of the new 15c. I have installed a strong Brownian Motion producer (say a nice hot cup of tea) into the battery compartment which drives the LED display.

Another view:

[d b]

(03-30-2016 05:12 AM)Geoff Quickfall Wrote:  I have installed a strong Brownian Motion producer (say a nice hot cup of tea) into the battery compartment which drives the LED display.

Geoff; That's Infinitely Improbable.

[PANAMATIK]

(03-30-2016 05:12 AM)Geoff Quickfall Wrote:  ..... I have installed a strong Brownian Motion producer (say a nice hot cup of tea) into the battery compartment which drives the LED display.

Aren't you two days too early with your inventions?

Bernhard

[Didier Lachieze]

(03-30-2016 03:54 PM)PANAMATIK Wrote:  

(03-30-2016 05:12 AM)Geoff Quickfall Wrote:  ..... I have installed a strong Brownian Motion producer (say a nice hot cup of tea) into the battery compartment which drives the LED display.

Aren't you two days too early with your inventions?

This is the proof Geoff has also invented a time travel machine

[Geoff Quickfall]

That's why I said, in post seven, that since I wouldn't be home on the first of next month :-)

Still not home yet. Won't be until the 5th of next month: April.

d:-D


Dave, yes the Drill particles may be a problem. I have a board here for experimenting with. I will see if melting a hole may be a better option.

[Dave Frederickson]

(03-30-2016 12:54 AM)Katie Wasserman Wrote:  I can't wait to read that chapter, especially the part about the micro-miniturized cold fusion reactor that you've come up with to power it!

A flux capacitor would work well in this application.

[Geoff Quickfall]

Hhahaha!

So many literary quotes and alluding's (not a word apparently) too.

Dave , that's just silly, every one knows you need a Delorian and the flux capacitor is far to large! I hollowed out an electrolytic cap and filled it with earl grey. I was going to use one of these:



You can get that battery at radio shack, but they were all out.



iPad central email facility: Sent on April 4th, 2016

[HP67]

A nixie tube wristwatch? When this baby gets up to 5:30 you're gonna see some serious $^&*

[Dave Frederickson]

(03-30-2016 04:54 PM)Geoff Quickfall Wrote:  Dave , that's just silly, every one knows you need a Delorian and the flux capacitor is far to large!
iPad central email facility: Sent on April 4th, 2016

Actually, SMT technology has progressed significantly since 1985 and flux caps are available in much smaller packages.



I thought you were going to give me a hard time about the 1.21 GW necessary to get the thing going, but I see you've improved on Mr. Fusion and reduced it's size as well.

Besides, you're just powering a 15C, not sending it back to the future.

Dave