[HP-35s] Are bad keys fixable?

[Marcio]

Hello all,

My 35s has gone 'non-programmable'. The R/S key died this morning. I searched the old forums and saw quite a few complaints about 35s missing keystrokes and dead keys but none mentions anything about fixes.

Does this inconvenience have a solution or should I just get another machine?

Very much appreciated.

[Logan]

I'm terrified that this will happen to me some time right before or during the PE exam. I'll have a backup calculator but don't want to have to re-enter all my programs.

[Marcio]

Logan, as much as I hate to say it, the truth is that the 35s can't be trusted for serious use. I have a couple of programs on it but none is important enough that would cause me trouble if erased.

The quality is just not there, which is a shame because I like the 35s, its solver, speed (if compared to my trusty 15c) and memory for data and programs.

I decided not to buy a new one. A used 42s in good condition costs more than I can afford so I think I will be back to free42 on my droid phone when not at home.

[Ron Ross]

A used Hp 17Bii in good shape is very common and inexpensive. True, it doesn't have trig functions, but it is a smaller and better built pocket calculator than an Hp 35s. And it has a better solver, that really allows you to input all the conversions and other features you do need in long variable descriptive names (admittedly, six characters, but 6>1).
.
I have a 35s and while I like it, I like it least among my many HPs.

[Logan]

Marcio, my preferred calculator is a used 42s I picked up, but until October I must use the 35s as it is the only (decent) RPN or programmable calculator allowed for the PE exam.

But sure looking forward to the DM42.

[Martin Hepperle]

(08-23-2016 01:26 PM)Marcio Wrote:  Hello all,

My 35s has gone 'non-programmable'. The R/S key died this morning. I searched the old forums and saw quite a few complaints about 35s missing keystrokes and dead keys but none mentions anything about fixes.

Does this inconvenience have a solution or should I just get another machine?

Very much appreciated.

Hi,

I had some success in "fixing" a key on a HP35s bought off eBay. Its "+" key required a stronger press to register. I flushed the keyboard with a larger dose of alcohol (pure isopropanol - beer, wine and whiskey are less suitable). Used a syringe to squeeze the liquid between key cap and front panel a few times, shook droplets off and left to dry.
Also worked for a HP 10B with a non registering key. At least worth a try.

Martin

[Marcio]

(08-23-2016 09:33 PM)Ron Ross Wrote:  A used Hp 17Bii in good shape is very common and inexpensive. True, it doesn't have trig functions, but it is a smaller and better built pocket calculator than an Hp 35s. And it has a better solver, that really allows you to input all the conversions and other features you do need in long variable descriptive names (admittedly, six characters, but 6>1).
.
I have a 35s and while I like it, I like it least among my many HPs.

I appreciate the tip very much but I prefer the scientific kind. Will probably pick up a 32s.

(08-24-2016 01:28 PM)Martin Hepperle Wrote:  Hi,

I had some success in "fixing" a key on a HP35s bought off eBay. Its "+" key required a stronger press to register. I flushed the keyboard with a larger dose of alcohol (pure isopropanol - beer, wine and whiskey are less suitable). Used a syringe to squeeze the liquid between key cap and front panel a few times, shook droplets off and left to dry.
Also worked for a HP 10B with a non registering key. At least worth a try.

Martin

No luck. I gave it to a friend at work who isn't interested in programming. Switched it over to ALG and should serve him for a while.

Thank you for the tips.

[Thomas Radtke]

(08-24-2016 11:09 PM)Marcio Wrote:  I appreciate the tip very much but I prefer the scientific kind. Will probably pick up a 32s.

The 32SII adds an equation editor/solver, not nearly on a par with the RPL-solver but still useful. Be aware it has very little memory.

[Logan]

(08-25-2016 07:30 AM)Thomas Radtke Wrote:  The 32SII adds an equation editor/solver, not nearly on a par with the RPL-solver but still useful.

What is the RPL-solver and is it only available on the graphing calculators?

[Thomas Radtke]

(08-25-2016 10:34 AM)Logan Wrote:  What is the RPL-solver and is it only available on the graphing calculators?

HP developed an OS first used in the 18C, RPL. Is has been used on the 27S also besides the well known RPL-calculators. This OS provides the solver and the user interface known from e.g. the 17b, if I'm not completely mistaken.

The imo best scientific pocketable calculator (if the Clamshells 28C and 28S aren't counting) offering it is the 27S, but alas no RPN :-(.

[Jeff O.]

Many moons ago I tore down a 35s, details here. Unfortunately, the place where I hosted the pictures went away, so there are no pictures. (I probably have the originals somewhere, but it might take me a while to find them.) Edited disassembly description is as follows:

Remove the rubber plugs in the four corners of the battery compartment, then peel off the rubber strip on the bottom of the calculator, and remove the six screws. The front and back halves of the case are also held together by five plastic catches, one in the middle on the top edge, one in the middle on each side, and one near the bottom on each side. These catches are not exceptionally tenacious; some gentle tugging at the case halves and careful prying between them will fairly easily separate the front and back.

Remove the 25 small screws that appear to hold down the PCB, but this will not free it. Close inspection will reveal that the posts into which the screws were screwed are mushroomed over at the top, just like the heat stakes in other HP calculators. Trim the posts off flush with PCB, and with a little gently prying, the PCB will be freed up. Once the PCB comes out, next is a thin rubber membrane, then the keys themselves. The keys are in two groups with a number of keys connected to a plastic frame, with the four cursor keys adhered to their own separate rubber membrane.

The front side of the main PCB is covered with a thin sheet of white plastic of some sort. There a little bumps visible through the plastic that appear to be metal dome key contacts. Assuming the technology is similar to the 30b (one of which I have torn down to the point of removing a similar membrane), that white plastic sheet is stuck to the PCB and the metal domes are stuck between the sheet and the PCB. So you might be able to peel off the sheet, clean the offending dome and the PCB, re-stick the sheet and re-assemble. Although I tore down a 30b to the point of removing the sheet, I never attempted to re-stick it, so I cannot guarantee that this will work. But if the alternative is getting a new machine, it might be worth a try.

[Marcio]

Jeff,

After much consideration, I decided to buy yet another 35s unit (the 2nd second-hand one, 3rd overall) a couple of days ago. There were several bad keys on this one. Some needed much more force to respond, namely COS, SQRT (required a very firm press, much like the R/S on the 2nd one), y^x, +/-, E, () and 8. So 7 keys overall. I noticed these keys are close to each other so I suspected there was something other than low quality causing all that trouble. Long story short, I gave the 35s a good bath with regular alcohol in a plastic bowl, and was careful to save the display. Well, I was actually surprised by the amount of residue resulted from the manufacturing process, should have taken a picture.

Well, I am happy to report the 35s is now fully functional (let's hope it stays like this long enough to justify getting another one) and the other one with the bad R/S key is gonna take a bath as well.

To remove moisture and related, I let it rest for 24 hours, disassembled it and used a hair dryer to speed up the drying.

Also noticed the capacitors are different on the these machines. HP was able to change the hardware but not the software and it's been almost 10 years since introduction. If only the bath could wash out all those bugs as well.

Thanks.

[ndzied1]

(09-16-2016 01:18 PM)Marcio Wrote:  If only the bath could wash out all those bugs as well.

Thanks.

Am I right that you disassembled the unit before the alcohol bath?

The capacitor color might have been changed at the manufacturer's discretion if they had the same specs as the originals.

[Marcio]

(09-16-2016 07:48 PM)ndzied1 Wrote:  Am I right that you disassembled the unit before the alcohol bath?

No, I did not but I could have. I had to disassemble it after the bath to make the drying easier and faster. The thing is that disassembling the 35s is troublesome and almost always leaves dents etc. The calculator has a big opening on its back that is covered by the battery door.
Pure alcohol (C3+) is preferred over regular alcohol (C2+water).
If you are willing to give this a go, use a white bowl and take pictures of the alcohol, if you can.

(09-16-2016 07:48 PM)ndzied1 Wrote:  The capacitor color might have been changed at the manufacturer's discretion if they had the same specs as the originals.

It was not just the color, but nearly a whole set of capacitors. I have a picture of that if you're interested. My point is, if HP is still manufacturing the 35s after almost 10 years, why not work on a 35sII? Since the target is exams, anything beyond the 35s/TI36xPro capabilities won't be allowed. Maybe faster, smaller and with STO unshifted.