HP 32S Repair

[jhg]

I have a 32S that suffers from the non-responsive keys problem due to the keyboard/PCB contact issue. It can be temporarily ameliorated by squeezing between the display and top row of keys.

I followed the instructions on opening the case (took a LOT of force to get the bottom rivets to pop) and was successful, but twisting the PCB mounting tabs did not resolve the issue and I'm afraid to twist more for fear of breaking them.

What to do in this situation?

[Nick]

(09-10-2016 05:48 PM)jhg Wrote:  ...It can be temporarily ameliorated by squeezing between the display and top row of keys

This may or may not be related to your issue, but could give you some ideas:

I'm not familiar with the 32S hardware -- maybe someone else has a more proper fix (try at your own risk).

I fixed my HP-15C key "rattle" in one corner by unscrewing the back, using a sheet of paper as a spacer -- counting the right number of folds via trial/error (use scissors for other than powers of 2 and getting the right size for the area to cover), then reattaching the back. This provided just the right pressure for the keyboard to secure against in place of the stretched / popped rivets (rattle-free).

Yip,
Nick

Edit: Added Quote

[Ed Wright]

I have a 32Sii with the same problem. I have had no success fixing it. I've tried placing spacers on top of the connector, but it didn't work well and didn't last long. :-(

[Nick]

hp 48gx quick fix [YouTube]

[jhg]

(09-11-2016 05:32 AM)Nick Wrote:  hp 48gx quick fix [YouTube]

I've been doing that for awhile now, it no longer works.

It would be nice to know what causes the PCB-keyboard connection to fail like this. Is it dust getting into the pads and interfering with the connections? AFAICT the pads are gold so corrosion shouldn't be an issue. Does anybody know?

If there were a definite answer I could decide if I wanted to try untwisting the tabs, to remove the PCB and clean out any dust. But that sounds risky and I don't want to do it unless there's a good chance it will fix the problem.

[BartDB]

Hi,

The problem is that there is a rubber strip pushing the keyboard contacts against the PCB. This rubber deteriorates.

The best solution is to take the PCB off and replace the rubber under the keyboard contact strip (just under the screen). As you have already worked the twist tabs, you'll have to be careful loosening and refastening them.

See the middle of the page here where it says "HP48G Keyboard Connectors":
http://users.ju.edu/hduong/repair/
(the construction of the 32s is similar. Do not remove the metal keyboard plate, just lift up the connector strip to see the deteriorated rubber strip.)

I have successfully done that to several 48 models.

-B

[jhg]

(09-12-2016 03:04 PM)BartDB Wrote:  The problem is that there is a rubber strip pushing the keyboard contacts against the PCB. This rubber deteriorates.

The best solution is to take the PCB off and replace the rubber under the keyboard contact strip (just under the screen). As you have already worked the twist tabs, you'll have to be careful loosening and refastening them.

Thanks, I guess I'll try this when I have a little time.

[Marcio]

(09-11-2016 12:28 AM)Ed Wright Wrote:  I have a 32Sii with the same problem. I have had no success fixing it. I've tried placing spacers on top of the connector, but it didn't work well and didn't last long. :-(

Folded. Had promised myself I would never buy a "modern" HP calculator again.
I have had 3 35s units so far, and it's been 2 years only since the first one. Bought the 3rd one just yesterday. Fingers crossed.

[aj04062]

A very good "spacer" to ADD is a normal rubber band.

[gaster]

(09-12-2016 04:57 PM)Marcio Wrote:  

(09-11-2016 12:28 AM)Ed Wright Wrote:  I have a 32Sii with the same problem. I have had no success fixing it. I've tried placing spacers on top of the connector, but it didn't work well and didn't last long. :-(

Folded. Had promised myself I would never buy a "modern" HP calculator again.
I have had 3 35s units so far, and it's been 2 years only since the first one. Bought the 3rd one just yesterday. Fingers crossed.

I am lucky enough to live near a Frys store. A few weeks ago they had the 35s on sale for $29 so I got a couple. I already have an older one, made in China, and the buttons are a bit sketchy. Some are a bit mushy so it's hard to know if the click registered or not. Of course I got this calculator used from TAS so I don't know what it was like new.
Anyway, one new 35s I opened is made in the Philippines and the buttons are a bit different. They seem a bit stiffer, no mushy feel, and they have a much more clear and distinct click. Only time will tell if they stay this way or get mushy. For now I'm happy though. I mostly use the calculator for fractions at work. Any calculator would work really, but I have my RPN tendencies when under pressure.

Edit: In case anyone was curious, the Philippines serial number I have starts with PHA. Maybe everyone else was already aware of this, but I haven't seen a Philippines version before.

[jhg]

I tried removing the PCB today. It was easy and the twist tabs did not break.

I cut a slim piece of card stock 1.25" long and 1/16" wide to go between the keyboard contacts and the foam rubber that holds them against the PCB, and reassembled.

The good news is that the keyboard works great, but the display is now missing dots. The display electrical contact is a thin strip of rubber with embedded vertical conductors that contacts some pads on the PCB at the top of the display (opposite the keyboard contacts). Clearly this requires extreme precision alignment and even though everything looks like it's correctly aligned, either some dust got in there in spite of my being careful, or the alignment is off.

I was able to remove the PCB a second time and carefully cleaned the contact strip and pads but on reassembly the display problem is worse.

Oh well.... sigh. At least I tried.

[mfleming]

Hi jhg,

I've repaired a half dozen Pioneers in the manner you describe and never had a problem with the display. You need a steady, fairly hard, downward pressure on the PCB as you tighten the twist tabs to insure a good contact between PCB pads and their contacts below. Keep the little tab wings pointed down, not folded up.

You probably have another three or four tries before the twist tabs break, so give it another try

~Mark

[Logan]

I just repaired a 32SII and when I first tried to put the PCB back on, I also had the display missing some dots in the numbers (they looked something like dashed lines making up the numbers). I realized that one of my ties was not firmly in place, so like the above poster also said, I applied pressure, then twisted the tie until it was snug and it works perfectly now.

It should be easier to get the calculator apart now and you shouldn't even have to take the PCB off.

[BartDB]

As others have said, try to tighten the twist tabs a bit more. Especially carefully try to push the downward facing hooks out a bit.
   

[jhg]

Success!!

(09-18-2016 01:46 AM)mfleming Wrote:  I've repaired a half dozen Pioneers in the manner you describe and never had a problem with the display. You need a steady, fairly hard, downward pressure on the PCB as you tighten the twist tabs to insure a good contact between PCB pads and their contacts below. Keep the little tab wings pointed down, not folded up.

You probably have another three or four tries before the twist tabs break, so give it another try

~Mark

Thanks for the encouragement. I removed the PCB again (4th time now), and examined the rubber contact strip under a magnifier. I found some dust, so I carefully cleaned the strip and PCB contacts with a lintless "pec-pad" and methanol based cleaning solution (digital camera sensor cleaner), and reassembled once again after straightening the pins on the twist tabs.

Keyboard and display are now back to normal.

I popped the bottom "rivets" back in and they feel pretty solid, but the top rivets, having had their tops drilled out, leave the case feeling loose. Is there a recommended method for reattaching them? I'm thinking a small drop of epoxy in a couple of them would work.

Thanks!

[Logan]

Good news!

[mfleming]

Yay, we have another winner! Great to get one of the old guys working again. Regarding securing the case halves together, one idea I've considered (but haven't tried yet) is using a self-tapping screw of the appropriate size. The two top posts have holes in their center through which the screw can follow. The screw head would need to fit the recess in the bottom case. That should secure the halves together and still let you open the case for repair if needed.

Give it a try and let us know how it works out!
~Mark

[PANAMATIK]

The HP-32S was my daily calculator for more than 25 years. I'm happy about your success. My congratulations!

Bernhard

[jhg]

(09-19-2016 07:19 PM)mfleming Wrote:  Yay, we have another winner! Great to get one of the old guys working again. Regarding securing the case halves together, one idea I've considered (but haven't tried yet) is using a self-tapping screw of the appropriate size. The two top posts have holes in their center through which the screw can follow. The screw head would need to fit the recess in the bottom case. That should secure the halves together and still let you open the case for repair if needed.

Sounds good. I found a local Ace Hardware that stocks miniature #0 and #00 1/8" screws, one of which which should be about the right size. I'll post after I've had a chance to try it (probably in a couple of days).

Thanks again to all the people who replied. I entered college in 1972 at almost exactly the same time the HP-35 was released, and it was the hot status symbol for a few rich kids (not me) whose parents could afford the price (about $2000 in today's dollars). My 32S feels like an old friend, and I really wanted to avoid having to replace it. I'm disappointed that RPN never caught on, as I find it much more intuitive than algebraic entry.

[mfleming]

(09-19-2016 09:17 PM)jhg Wrote:  Sounds good. I found a local Ace Hardware that stocks miniature #0 and #00 1/8" screws, one of which which should be about the right size.

There's an old machinist trick for adjusting the fit of a pin in a hole from loose to tight that you can use. First, use a screw whose head will be recessed below the bottom face of the case when screwed fully in, because otherwise the head will interfere with the cover as it is slid back into place. A #4 socket head screw is slightly too big for the hole in the calculator bottom half, so a #2 or #0 flat head or round head screw should work. A tapered sheet metal screw would work best, but a regular machine screw can also do the job. With either screw type, you may need to widen out the post hole a bit using the proper tap drill size.

Then thread the screw all the way into the post hole with the case halves together. If the halves are a tight fit, you're done, as the outward pressure of the screw on the post diameter is enough to tighten the post in the hole. If not, remove the screw, separate the case, then split the post down through the middle of the hole using a fine saw or Xacto blade. You'll probably only need to split the post no more than half the way down.

Assemble the case halves and thread the screws back in. As they go in, they will push the two post halves out and against the hole in the case bottom. Bingo, a nice tight fit! Should keep the case from popping apart if you drop it.

Quote: I entered college in 1972 at almost exactly the same time the HP-35 was released, and it was the hot status symbol for a few rich kids (not me) whose parents could afford the price (about $2000 in today's dollars).

Hey! I was one of those "rich kids" but it wasn't my parents who bought me my HP Scientific Calculator! (1302A29315) Nosiree, it was six months as a McDonalds fry cook and Howard Johnsons night clerk after class, saving every single penny - Every! Single! Penny! - not withheld by the government to get enough for it. You're right about the "hot" part though - in the spring of '73, even the prof's would ask if they could try the calculator

Sidenote: if you really want to see the weird side of humanity, try working as a night clerk at a motel for a few months!
~ Mark