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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 16th Aug 2021, 12:25 pm   #1
ThomasPlummer55
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Default TI-30 Calculator Bounce Fix

I have a fix for the TI-30 bounce problem.

Last edited by Cobaltblue; 16th Aug 2021 at 1:27 pm. Reason: Uncontrolled links not accepted from new members
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Old 16th Aug 2021, 1:30 pm   #2
Cobaltblue
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Default Re: TI-30 Calculator Bounce Fix

Hi Thomas and welcome to the Forum.

Sorry to have to delete your link.

I am sure you understand to prevent Spam we don't allow links of this sort from new members.

Perhaps you could copy your fix into posts within the forum?

Cheers

Mike T
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Old 16th Aug 2021, 9:34 pm   #3
turretslug
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Default Re: TI-30 Calculator Bounce Fix

Wow, that's bought back some bad memories, some involving picturesque vocabulary! I still have one of these from schooldays, it seems a shame to ditch it but I'm certain that the contacts won't have improved with age and disuse.
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Old 20th Aug 2021, 12:01 pm   #4
ThomasPlummer55
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Default Re: TI-30 Calculator Bounce Fix

Thanks for your note. I have a .doc with a complete guide with pictures how to fix the TI-30 Bounce Problem. How can I copy this file into your forums?

Thanks, Thomas
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Old 20th Aug 2021, 1:02 pm   #5
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Default Re: TI-30 Calculator Bounce Fix

Follow the instructions in this thread:-

https://www.vintage-radio.net/forum/...ad.php?t=77650

It refers to all kinds of attachments, including .doc files, not just pictures.
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Old 22nd Aug 2021, 5:30 pm   #6
ThomasPlummer55
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Default Re: TI-30 Calculator Bounce Fix

TI-30 Bounce Problem Solved

I really like LED calculators. The TI-30 was very popular even though it had the fatal flaw bounce problem. The TI engineers thought that spot welding the keyboard matrix wires and then embedding the wires in plastic was a good idea….. they were wrong. The difference of thermal coefficient of expansion of plastic and metal wires broke the spot welds. So if the calculator was exposed to winter temps and then brought indoors that was enough to rip these spot welds apart.
THE FIX **************
There are eight keyboard matrix wires that are spot welded. These are grouped in four closely spaced pairs. Each wire must be bypassed with a small wires soldered to the cross conductors at one edge of the keyboard. These connections are accessed by peeling back the sticky membrane carefully on one edge and bending up the connections you want to solder to. The effect of this fix is to make eight parallel connections which do what the spot welds should have done (stay connected). The photos show the details of two TI-30s which had severe bounce problems and now have none. Note: If the battery compartment is clean, no corrosion of any kind, then cover the keyboard surface with packing tape to cover all the visible holes. Any corrosion destroys the TI-30 keyboard and it cannot be fixed.

If you do this fix you will have a TI-30 that will work perfectly with never a bounce.
Good luck.
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Old 22nd Aug 2021, 5:36 pm   #7
ThomasPlummer55
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Default Re: TI-30 Calculator Bounce Fix

Thanks Station X, I have reformed the info so it complies with your rules.
Text and two pictures already submitted.
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Old 31st Jan 2024, 3:58 pm   #8
ThomasPlummer55
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Default TI-30 Calculator Bounce Fix Update

I have previously posted details of how to fix the bounce problem of TI-30 calculator under the title:

"TI-30 Calculator Bounce Fix" on this forum.

After more testing I found that I did not entirely fix the problem:

I have four TI30 calculators from 1977 era. Some have the key bounce problem. Over the years I have tried to analyze and fix this. I thought I had a permanent fix which was based on the premise that the keyboard pulse and sense wire welds were bad.
I was wrong. I destructively tested a keyboard and found that the welds welds were so good in fact that I had to use a lot of force to rip them apart. I have lately discovered that the key bounce problem seems to be greatly affected by the foam sheet between keys and dome switch assembly, for instance if I remove the sheet, key bounce really increases. So I am left pondering the effect of 46 years on the physical properties of this elastomeric foam sheet as well as the properties of the adhesive plastic sheet which encapsulates the metal dome strips. For now I plan to try other sheet material to see if I can eliminate the bounce.
I think the TI engineers debounced the keys in the main chip based on the properties of new keyboard material and that they were very close to the edge of bouncing which the passing years made evident.
I have researched this problem extensively on the web without finding a good fix.
Would like to hear from anyone who has worked on this.

Best regards,
Thomas
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Old 1st Feb 2024, 8:53 pm   #9
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Default Re: TI-30 Calculator Bounce Fix

Hi

I had a new TI-30 back in 1978 and recall it worked reliably for about three years then found the repeat digit problem occasionally happening. At the time, I didn't look into the problem but I've also come across similar problems with other calulators that use that type of keyboard. I noticed the problem was quite bad on a programmable Texas calculator, their first LCD model circa 1982.

What I've found on a number of occasions is a problem with the spring metal contacts. I think they have three outer and one large central dimple that make contact on the keyboard proper. The contact faces become slightly tarnished causing erratic operation. I've carefully polished these contact faces and it seems to have solved the problem.

Regards,
Symon
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Old 2nd Feb 2024, 10:56 pm   #10
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Default Re: TI-30 Calculator Bounce Fix

I had a TI-30 bought new from Comet, the keyboard soon went the way they all did.

It was out of warranty, but they replaced it with the closest thing they had - a programmable TI-55, which I still have. Still works perfectly, 40-odd years on.
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Old 7th Feb 2024, 8:24 am   #11
mark_in_manc
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Default Re: TI-30 Calculator Bounce Fix

Quote:
Originally Posted by Philips210 View Post
What I've found on a number of occasions is a problem with the spring metal contacts. I think they have three outer and one large central dimple that make contact on the keyboard proper. The contact faces become slightly tarnished causing erratic operation. I've carefully polished these contact faces and it seems to have solved the problem.

Regards,
Symon
Since this thread appeared, I have dug out one of these and yes, it has the problem (but also - yes it works, which I didn't know until this thread prompted me!). It looks like it comes apart by taking the battery cover off and then (somehow) bending three plastic tabs back to pop the top off...is this is way to do it? I ask as I am prone to snapping things in this kind of situation.
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Old 7th Feb 2024, 1:31 pm   #12
Philips210
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Default Re: TI-30 Calculator Bounce Fix

Hi Mark

I'm sorry I don't have the TI-30 any longer and it was many years ago when I repaired it. The three tabs that you mention seem familiar. Perhaps another member might confirm the best way to dismantle the case.
As with some remote control handsets, it's often a good idea to gently warm up the case with a hair drier to make it less likely for any pieces to break off.

Regards,
Symon
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Old 12th Feb 2024, 2:01 pm   #13
mark_in_manc
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Default Re: TI-30 Calculator Bounce Fix

Jogged elsewhere on the forum (and I really should not have needed the jog) - thank you Symon!
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Old 12th Feb 2024, 6:10 pm   #14
Philips210
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Default Re: TI-30 Calculator Bounce Fix

Hi Mark.

Did you manage to get it apart without any problems?

Regards,
Symon
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Old 12th Feb 2024, 9:49 pm   #15
mark_in_manc
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Default Re: TI-30 Calculator Bounce Fix

Not yet! Various family pressures have intervened - but meanwhile my 16 yr old (who is lower 6th and doing maths-phys-chem) is marvelling at it's ancientness

If I can get the Sinclair Programmable to work which I found in the same pile of junk, perhaps she can get to the bottom of reverse Polish whatever-it-is for me...
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Old 16th Feb 2024, 5:24 pm   #16
ThomasPlummer55
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Default Re: TI-30 Calculator Bounce Fix

New research and restoration tips for TI-55-II


16 FEB 2024

TI-55-II restoration

I have recently completed the restoration of a TI-55-II calculator circa 1984

My research showed that this was the worse model for key bounce problems and so I decided to focus on this as a challenge to restore. Based on other restorations I had done on TI30 and TI55 calculators circa 1977, I used my acquired skill on the TI-55-II

As received I could not enter the digits 1-8 without bounce after ten attempts so this one really had the defect.

GENERAL NOTES

On disassembly I noticed that the foam sheet was perforated where it touched the keys. It was also a bit sticky. I folded it over to 4x thickness and squeezed it and observed that it simple crushed to a thin layer and stuck together, the layers sticking to each other. Over 43 years the resilient foam had become an adhesive.

I had a TI30 foam sheet that was resilient and non sticky so I used it.
The process was as follows

Remove old foam and clean the key nibs with alcohol
Create and install 9 small 10 mil plastic pressure pads over welded spots on dome switch assemble
Put TI30 foam sheet back in, a little short but still covers keys
Cut a 5 mil mylar sheet the same size as the keyboard white plastic and place over foam
Reassemble

TESTING

Exercise the keyboard by firm pressing all keys ten times
Lay calculator on hard surface
Enter the numbers 1-8 ten times and look for bounce, repeat this 10 times
Also enter 1-0-1-0-1-0-1-0, and 9-6-9-6-9-6-9-6 ten times per set to get 0 and 9 coverage

In my case no bounce was seen in 800 consecutive key strokes.

Note on welds

It has been observed by another researcher that welds have been defective in his TI calculator project, that is to say they were no longer welded together but just touching. Now this could have occured at the factory or over time. I have destructively tested two TI30 keyboards and found solid and strong welds requiring a lot of force to break, so I cannot confirm his observations in my limmited testing.

Now I found that the behavior of this TI-55-II without pressure pads was different when held in the hand or laying flat on a hard surface. In the hand occaisional bounce was seen, and almost none when laying flat. I concluded that slight twisting and bending on the dome switch assemble was occuring. The unit is slim and thus unable to resist bending and twisting by hand use.
I surmised that this change in behavior could be do to some defective welds, just touching.
To reduce this effect I wanted to apply some pressure over the welded spots to force the two metal contacts together. This was done with 10 mil small plastic shims and a litle superglue to hold them in place. The pads focus pressure on the welds. The layers in order are: a sheet of foam, then a sheet of 5 mil mylar pressing against the dome switch assemlby and leaning on nine pressure pads.
Bad welds may be the reason but it could also be slight changes in the way the snap dome switch hits the wire contact. I have a method of directly testing welds that I have not yet put into practice, this would settle the issue by direct observation.

The pressure pads greatly reduced the bounce when hand held.
I have not been able to completely eliminate the hand held rare bounce but I will say that the unit is very usable for all tasks.

For 40 years this problem has not been solved. I seem to have a talent for doing these kinds of things, the proof being that this restoration was completely successful.

I hope these notes help you fix your own TI calculators.
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Old 16th Feb 2024, 10:22 pm   #17
Joe_Lorenz
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Default Re: TI-30 Calculator Bounce Fix

Thomas,

thank you for publishing this abstract! That is not only a new territory conquered in a nice and smart way but a great read also.
Yes, somewhere I must have an old TI 58 calculator, too, but back in the days I always used to prefer Commodore calculators.
My PR-100 had to be powered by my motorcyle accumulator when it came to burning the midnight oil. I am sure it did never suffer from bouncing but eating up battery power quickly!

Joe
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