HP-21 Disassembly Help...

[PANAMATIK]

(03-30-2016 04:54 PM)Geoff Quickfall Wrote:  

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

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

As you might know, most of these wonderful old FLUX-01 watches are damaged by battery leakage. But there will be a PANAMATIK repair kit available in april 4th. It includes decontamination antiflux paste and cryotablets reducing the heat to below 1000 degrees. Price will be about only 80M$ the kit for DIY.

Bernhard

[BobVA]

(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.

I was just inside my two, and they *both* have the holes - photo here. Maybe something to do with production dates?

[Geoff Quickfall]

Jeff?

Does yours have holes?

Would make the fix so much easier!

http://www.ebay.ca/itm/3-pk-combo-DeoxIT...OSwGzlTxav~

I buy these and use the red formula for suspected corrosion damage.

[Jeff_Kearns]

(03-30-2016 11:48 PM)Geoff Quickfall Wrote:  Jeff?

Does yours have holes?

Geoff,

    - The pic attached is the closest I have gotten to opening up the HP-21. My immediate problem is MUCH more basic than what you and Katie are suggesting. I can't even separate the faceplate from the body of the calculator. I am afraid of breaking it... It is supposed to swivel on the bottom 'hinge' but I can find no evidence of a hinge... As for holes, I 'think' it has them. Hopefully the picture comes through otherwise I have to email it/them to you.

Jeff

[Geoff Quickfall]

Good news, you have holes.

Now to get in. Not a hinge but a slot receiving a tab.

Watch this video:

https://ca.video.search.yahoo.com/video/...=ipad&tt=b

1) Remove battery pack.
2) remove two screws located under rubber feet at top of calculator.
3) as pictured, separate the upper portion pivoting on the lower section.
4) as you pivot, notice the battery contacts are preventing you from separating the two halves.
5) push gently on the contacts in a Motion to clear the battery compartment.
6) voila!

Now take some deoxit red and apply some to the hole under the offending key. Work a fine wire into the hole and twirl it as Katie mentioned. Work the key numerous times. Assemble is the reverse making sure the contacts clear the battery compartment.

Looks like steps one through three are complete, just ensure the contacts clear the compartment, as this is where the hangup is.

There is a trick which the HP people use but that takes even longer to describe but is pictured in the video.

Geoff

[BruceH]

(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:

Ah, the HP-15C LE -- Light Emitting

[Geoff Quickfall]

Good one Bruce!

Jeff, did you get it open?

Geoff

[Jeff_Kearns]

(04-01-2016 05:18 PM)Geoff Quickfall Wrote:  Jeff, did you get it open?

Geoff,

Thanks so much for the helpful video! It explains everything. I do not yet have the deoxit red so will wait until tomorrow to open it and effect the repair once I get the contact cleaner (hopefully available at fine hardware stores in the Ottawa area...).

I will report back with results of my repair efforts forthwith.

Thanks again,

Jeff

[Geoff Quickfall]

Myabe not hardware stores in Ottawa, try an electronics shop or the Source (radio shacks replacement).

I am in vancouver and source mine from eBay in those limits tubes.

Geoff

[Jeff_Kearns]

(04-02-2016 02:49 AM)Geoff Quickfall Wrote:  ...try an electronics shop or the Source (radio shacks replacement).

Geoff - I managed to find a can of deoxit red at an electronics store in Ottawa called Gervais Electronics. I looked all over... Boy I miss Montreal. They had a ton of electronics stores.

Now I have the following problem preventing me from pressing down on the battery prongs to release the keyboard top, as shown in the attached screen-grab from your video.    

I took a picture of the battery compartment in my HP-21 - see below. It is a rather crudely modified unit that the previous owner soldered together to accept AAs. The solder job is such that the prongs are bigger than the plastic slots so they won't go through!

I don't feel comfortable doing surgery on it without getting further advice... help.

Jeff

[Geoff Quickfall]

Aaaaarrrrrrgggggghhhhh!

Gues I better finish the book.

Pm sent Jeff!

This requires Solder removal! No mods need be taken on the calc for it to accept alkaline batteries. The only mod is to the battery holder. Remove the middle spine and the batteries will be replaceable. This happened to a 19c, had to remove the solder to expose the original battery contact rivets.

Geoff

[Jeff_Kearns]

(04-10-2016 06:51 PM)Geoff Quickfall Wrote:  Aaaaarrrrrrgggggghhhhh!

http://www.wikihow.com/Remove-Solder

Looks like I need a solder-sucker!

Jeff

[Geoff Quickfall]

Your typing to fast :-)

A de-solder station or de-solder iron with built in des older bulb is the best but the braid works well. Remember, flux is your friend. Read your pm.

Cheers

[Steve Simpkin]

(04-10-2016 06:51 PM)Geoff Quickfall Wrote:  This requires Solder removal! No mods need be taken on the calc for it to accept alkaline batteries. The only mod is to the battery holder. Remove the middle spine and the batteries will be replaceable. This happened to a 19c, had to remove the solder to expose the original battery contact rivets.
Geoff

I remember having to solder a small flat brass contact to the rivet that touched the positive alkaline battery post because it would not make reliable contact. Is there a better way because I could not get the positive terminal of the battery to make contact without doing something?

[Geoff Quickfall]

There is stress on the original rivet with solder connection. The springs are strong and can deform the circuit board extrusion that have the contacts attached.


This fatigues the contacts at two points.:

1) the circuit trace in which case the contact circuit must be bridged from the contact point to a contact point further into the circuit board.

2) the solder joint at the contact rivet.

I check the circuit with a continuity checker to ensure continuity. This doesn't preclude the failure under stress. So I initially apply flux and re-solder the rivet solder joint and test. Then work my way back along the circuit trace.

The washer trick works but may have inadvertently repaired either the cold solder at the rivet or a fatigue crack in the trace close to the contact rivet.

Geoff

[PANAMATIK]

I want to share my experience of cleaning a woodstock keyboard by completely removing the heat stakes.

After removing the top of the heatstakes with a scalpel I could separate the parts from each other and easily clean the keyboard contacts.

I decided to use a two component adhesive to fix the heatstakes. The bureau clips shown in the picture below were very helpful during hardening. It is very important that the parts must be as close together as before.

Be careful not to put any adhesive into he holes of the buttons

After applying the adhesive to the points indicated by the green arrows, I turned the keyboard around with the buttons upside laying on the table to avoid that any adhesive could flow by gravity through the holes into the keyboard. I didn't fix the heatstakes in the center of the keyboard for the same reason to avoid unwanted adhesive coming to near to the button contacts.







After cleaning the contacts, all buttons are working now flawlessly. The keyboard seems stable and I hope it will keep to be fixed for long time.

Bernhard

[Geoff Quickfall]

Good fix Bernhard!

Do the centre keys have the same snap as the edge keys?


The two component adhesive is epoxy I assume?


Geoff

[PANAMATIK]

(04-17-2016 05:31 PM)Geoff Quickfall Wrote:  Good fix Bernhard!

Do the centre keys have the same snap as the edge keys?

The two component adhesive is epoxy I assume?

Geoff

The center keys are working perfectly! No touch and feel difference to the other keys.

epoxy: See package print in image top left.

When I open a keyboard the sliders always have some sort of grease above the contacts. Do you know if this is important and which kind of material should be used?

Bernhard

[Geoff Quickfall]

They use a silicone grease. A light dab. The old grease tuns hard and becomes a barrier to current causing an intermittent switch.

Geoff

[Katie Wasserman]

(04-18-2016 03:18 PM)Geoff Quickfall Wrote:  They use a silicone grease. A light dab. The old grease tuns hard and becomes a barrier to current causing an intermittent switch.

Geoff

I've been using lithium grease for this, specifically this one