HP34C battery polarity

[Zaphod]

Just received my HP34C from far away, thanks, I asked for the sub-carrier and sleeves to be sent without the knackered cells.

I need to know one basic important thing before assembling some batteries and actually playing with it.....

Are the batteries like this (i.e. Neg on the left of shot):


or like this (i.e. Pos on the left of shot):


Do people prefer Nicad or NiMH ? (I will be charging externally for obvious reasons)

Any other hints and tips gratefully received.

[Archilog]

Looking at the back of the calculator, batteries up:

Code:


----------
|-88888888|
|+88888888|
----------

I use rechargeable NIMH batteries.

[Zaphod]

(05-07-2019 01:00 PM)Archilog Wrote:  Looking at the back of the calculator, batteries up:

Code:


----------
|-88888888|
|+88888888|
----------

I use rechargeable NIMH batteries.

Thanks for your quick response.

Do you use the original end link at the other end?, or pre-tagged NiMH's ?

[Archilog]

Aluminium foil, when I don't find my original cradle, much better.

[burkhard]

(05-07-2019 12:50 PM)Zaphod Wrote:  Do people prefer Nicad or NiMH ? (I will be charging externally for obvious reasons)

I think many people prefer NiMH, but specifically the Eneloop brand because are designed to suffer from self-discharge *much* less than typical NiMH cells. Self-discharge, cells going dead when in storage or the calculator is just turned off, tends to be a problem with most NiMH, so low self-discharge is a big plus.

[Zaphod]

Dagnammit

I tried a couple of used AA primarys I had knocking about, calc powered up.

Was playing with it for 10-15 minutes - all aok, then suddenly half way through keypresses the display died !!

I thought for a moment the batteries had become dislodged, but double checked and they were fine, I'd used copper take at the other end.

The calc is now dead to the world, terminal volts are pretty much spot on 3V....

I double-checked that people have used these with primary cells
(https://www.hpmuseum.org/cgi-sys/cgiwrap...read=15985)


So what's occurred I wonder?? - any ideas?

(The calc weighs ~175grammes to tell you which type it is/was)

[jebem]

Chances are that a bad contact in the power supply area is blocking the DC volrage to reach the main pcb.
Usual suspects are the battery connectors, the power cables going from the battery holder contacts to the main pcb, and the power switch.
Remove the batteries, open the machine case, use a multimeter to check for good continuity, meaning resistance values below 0.5 ohm on each power cable.
Sometimes a bad contact is found at the battery terminals as these use metal rivets to maintain electrical contact between the batery terminal and the flat cable. Dry electrolysis may cause oxidation here.
Also check for previous battery leakage. This for sure would cause corrosion and would need total disasembly to clean the components without the risk of destroy the keyboard faceplate.

[Zaphod]

The battery contact area was nice and clean, with no previous signs of corrosion.... nice shiny plated spring plates.

I’ll have to open it up when I get a chance soon. It’s at work now.

[burkhard]

(05-07-2019 02:04 PM)Zaphod Wrote:  The calc is now dead to the world, terminal volts are pretty much spot on 3V....

So what's occurred I wonder?? - any ideas?

I wager that the problem is that it is a Spice. Most of those were built using the innovative and stupid design of not soldering the chips to the board, but making electrical contact (usually, except when it doesn't) through case assembly clamping pressure.

A simple test that does not require opening it: With the batteries in and the switch turned "on", hold the top (display end) in one hand and the opposite end in the other hand. Exert a slight twisting torque first in one direction and then the other. Obviously, don't crank it far enough to crack anything, but a detectable degree or so of rotational displacement is in order. My bet is that it will suddenly come on, and will work for a while, until it needs to have the calculator chiropractor called in again.

[Zaphod]

(05-07-2019 08:42 PM)burkhard Wrote:  I wager that the problem is that it is a Spice. Most of those were built using the innovative and stupid design of not soldering the chips to the board, but making electrical contact (usually, except when it doesn't) through case assembly clamping pressure.

A simple test that does not require opening it: With the batteries in and the switch turned "on", hold the top (display end) in one hand and the opposite end in the other hand. Exert a slight twisting torque first in one direction and then the other. Obviously, don't crank it far enough to crack anything, but a detectable degree or so of rotational displacement is in order. My bet is that it will suddenly come on, and will work for a while, until it needs to have the calculator chiropractor called in again.

Well done that man, I knew about the clamped style versions of these (as I had a HP31e back in the day which I disassembled and discovered)
That's why I mentioned the weight earlier.

Anyway a slight twist and I got a dot !........ a dot !!

So a very gentle tap on the desk and et voila - it's back !!

I will have to strip it sometime and clean up.... at least it's not anything too dramatic.

I'm enjoying the red led effect for now... eyes goes misty ........ ahhhhhh

[Zaphod]

After a gentle clean up on the front with several cotton buds, it's like new considering it's 40 years old !!
And a complete collection of the supplied books etc makes it even nicer....
I'm very pleased.

[burkhard]

(05-08-2019 06:22 AM)Zaphod Wrote:  Anyway a slight twist and I got a dot !........ a dot !!

So a very gentle tap on the desk and et voila - it's back !!

My own 34C (and I think another of my Spice models) has the same issue. It's not so severe that I am inclined to open it up, yet though. I need to learn the technique on an otherwise-dead 38C, which is (especially since not-functional) a lot less valuable than the 34C.

I love that L.E.D. glow... so nostalgic and easy on the eyes.