HP 28S is very loud when opening/closing

[RK_]

I have just received an HP 28S that belonged to my uncle. It hasn't been used in sometime, and when I fold it open or closed it makes quite a squeaking noise. I am not afraid the calculator will break each time I open it, but it does seem like something I should address. The hinges are tight enough that when you open the calculator it will not simply lay flat on the table without more adjustment.

I am not sure if I will cause damage to the calculator if I add some oil around the hinges, or if that will stop the noise.

I would greatly appreciate any suggestions or other tips about this calculator!
Thanks,
RK

[ijabbott]

A tiny amount of pure silicone oil (suitable for plastics) worked into the hinges should be fine, even though the manual says not to lubricate the hinges.

[grsbanks]

Whatever you do, don't use a petroleum based oil such as 3-in-1 or similar. That will cause irreparable damage to the plastic.

Silicone oil is certainly one way to do it. Another is possibly one of the many "cube lube" products out there for lubricating Rubik's Cubes.

[Pjwum]

You are not alone!

[edryer]

Be VERY VERY careful with the battery door... very weak design flaw. Only open/close when absolutely necessary and if possible use flattop (rechargeable) AAA cells (thanks for advice to previous poster) to relieve door stress. Universal chargers charge these (the ones with adjustable battery size contacts).

My cells and charger coming in a few days and will keep the board updated!

[Massimo Gnerucci]

(01-30-2020 06:20 PM)edryer Wrote:  Be VERY VERY careful with the battery door... very weak design flaw. Only open/close when absolutely necessary and if possible use flattop (rechargeable) AAA cells (thanks for advice to previous poster) to relieve door stress. Universal chargers charge these (the ones with adjustable battery size contacts).

My cells and charger coming in a few days and will keep the board updated!

AAAs in a 28S??
It takes N cells.

[ijabbott]

(01-30-2020 08:22 PM)Massimo Gnerucci Wrote:  

(01-30-2020 06:20 PM)edryer Wrote:  Be VERY VERY careful with the battery door... very weak design flaw. Only open/close when absolutely necessary and if possible use flattop (rechargeable) AAA cells (thanks for advice to previous poster) to relieve door stress. Universal chargers charge these (the ones with adjustable battery size contacts).

My cells and charger coming in a few days and will keep the board updated!

AAAs in a 28S??
It takes N cells.

2/3 AAA maybe?

[Massimo Gnerucci]

(01-30-2020 08:58 PM)ijabbott Wrote:  

(01-30-2020 08:22 PM)Massimo Gnerucci Wrote:  AAAs in a 28S??
It takes N cells.

2/3 AAA maybe?

Maybe. Are they readily available? I never found them, anywhere.

[rprosperi]

(01-30-2020 09:07 PM)Massimo Gnerucci Wrote:  

(01-30-2020 08:58 PM)ijabbott Wrote:  2/3 AAA maybe?

Maybe. Are they readily available? I never found them, anywhere.

Plenty of sources for them on Amazon, at least in USA. Here's one, but there were at least a dozen others:

https://www.amazon.com/6pcs-3AAA-Recharg...B01NAHBOES

But I agree, I've never seen them in a brick-and-mortar store, despite hearing about them for many years.

[Massimo Gnerucci]

(01-30-2020 10:40 PM)rprosperi Wrote:  

(01-30-2020 09:07 PM)Massimo Gnerucci Wrote:  Maybe. Are they readily available? I never found them, anywhere.

Plenty of sources for them on Amazon, at least in USA. Here's one, but there were at least a dozen others:

https://www.amazon.com/6pcs-3AAA-Recharg...B01NAHBOES

But I agree, I've never seen them in a brick-and-mortar store, despite hearing about them for many years.

They seem to exist only in rechargeable format.
I've seen pictures of alcaline Energizer N batteries with a quite short cathode.

[burkhard]

Yes, he meant flat top "2/3 AAA". I had suggested them to him somewhere on here (PM?) as I find that they are a little bit shorter than the N cells and thus put less stress on that evil "designed to fail" battery door interface. I use them in my perfect 28 and they seem to significantly reduce the spring preload. I charge them using ogazent N-cell adapters in a La Crosse BC-1000 smart charger. The N-cell adapters work fine for 2/3 AAA as well.

I'm also *very* careful opening the door.

Regarding a lubricant:
With both plastic and electronics, one always has to be a little careful as far as lubricants are concerned. I use this low-viscosity silicone oil for many plastics applications and have yet to have it cause any trouble. I haven't tried it on squeaky clamshell HP hinges... yet, but I think it would probably be a good application.
Super Lube 56104 Silicone Oil 100 CST, Clear
https://www.amazon.com/gp/product/B00OBV...UTF8&psc=1

[edryer]

yes, thank you Burkhard, I did indeed mean your suggested 2/3 AAA, flat-top, apparently there are two types of flat top and one of them isn't truly flat top, your link was to the smaller (and suitable battery) - if any folk order these (other from burkhards link) and they are described as flat top I suggest looking to make sure they are truly the flat top variety (also known as Industrial in some places).

I have also seen 1/3 AAA batteries advertised, coupled with some dowel and aluminium foil this may also be a solution. One guy used 3 watch cells and dowel + aluminium (+ custom cover (http://mpshp.com/hp28s/Foto01.jpg) ) but 3 x 1/3 AAA may last quite a bit longer.

So another idea may be 3 x 1/3 AAA with dowel/aluminium foil which may truly relieve all pressure on the battery hatch!

The 28S is a fantastic device, and I note now that prices have risen the last few years, becoming far more collectable.

[striegel]

I suspect it may be risky to try something conductive like graphite, but how about talc or cornstarch?

Alan

[cruff]

(02-02-2020 08:41 PM)striegel Wrote:  I suspect it may be risky to try something conductive like graphite, but how about talc or cornstarch?

Talc is likely to be mildly abrasive to the plastic and cornstarch could swell in humid conditions. Either one is likely to get into the LCD eventually.