OT: HP41C

[Wendelin Uez]

My pocket calculator HP41C can no longer switche on via on-of-key, even not
by removing batteries..

Does anyone know how to "repair" this feature?

[Ed Cryer]

Post by Wendelin Uez
My pocket calculator HP41C can no longer switche on via on-of-key, even
not by removing batteries..
Does anyone know how to "repair" this feature?

The HP41C is a heirloom. It first came out in 1979.
If it has been switching on and off successfully until very recently,
then I say "nice piece of hardware".
I can't for the life of me see how removing the batteries might restore
the on/off key. Perhaps you might elucidate.
I've seen remotes lose the on/off switch after a mere handful of years.
The wear and tear does it.

Ed

[Paul]

My pocket calculator HP41C can no longer switche on via on-of-key, even not by removing batteries..
Does anyone know how to "repair" this feature?

If there are NiCd batteries, and those leak via their
pressure vent, that can be damaging to the printed circuit board.

A couple of the ICs are glob-top. There is a bare silicon die.
They wire bond the pads on the die, to the PCB. After the wire bonds
are made, a rubbery or plastic material is placed over the silicon
die to give it some protection. Whereas the main chip is a large
DIP. You could not allow humans to handle the PCB, if the bond
wires were exposed :-) They'd crush the bond wires.

The machine uses a boost converter, and converts from
battery voltage to circuit voltage, with switching. And apparently,
there is a fair amount of ripple in the voltage. Maybe some of
the components are CMOS rather than NMOS.

Loading Image...

https://www.hpmuseum.org/forum/thread-19379.html

The power switch would be in the battery portion of the circuit
(you can't leave the boost converter running constantly).
The boost converter has to work, in order for the machine
to "light up". A failure could be caused by:

Bad switch
Bad battery (common with NiCd and reverse bias plate-out inside)
Bad boost converter

The kinds of conversion are things like "linear" (not efficient),
"buck converter" (efficient), "boost converter" (slightly less efficient,
does not usually have huge power output). In the old days, they did not
know how to multiply the voltage value all that effectively on their boost.
If you do voltage multiplication with diode trees, you only get
a "whiff" of current from the output. The higher the boost ratio,
the more wimpy the output. It's simpler to use an inverter with
all the voltage ratio provided by a transformer. There isn't a
lot of room for a transformer in a calculator. But it can be done.
A long time ago, they invented "planar magnetics" for the purpose.
The converter with the planar magnetics, the very first one,
could produce 60 amps. And it fit in the palm of my hand.

Those HP calc circuits had their fair share of quirks. It's a wonder
anyone got output from them :-) They have the smell of
"hobby circuit" about them. And a pretty low clock frequency.
They don't even need a quartz crystal, to generate the clock.

Paul

[Paul]

My pocket calculator HP41C can no longer switche on via on-of-key, even not by removing batteries..
Does anyone know how to "repair" this feature?

There is a side view of the 30 pin DIP at the bottom here.
The disc could be part of a thermal solution.

http://www.vaxman.de/my_machines/hp/41c/41c.html

A block diagram of the design, is on the tenth page below.
The POR signal, could be the Power-On-Reset to
restore sanity to the main chip.

https://literature.hpcalc.org/community/hp41c-sm-en.pdf

And like the description says, they liked to do BCD arithmetic
back then. That is the "heritage of calculators". We use
binary arithmetic and conversions, on desktop computers.

Paul

[Sailfish]

Post by Paul

My pocket calculator HP41C can no longer switche on via on-of-key, even not by removing batteries..
Does anyone know how to "repair" this feature?

If there are NiCd batteries, and those leak via their
pressure vent, that can be damaging to the printed circuit board.
A couple of the ICs are glob-top. There is a bare silicon die.
They wire bond the pads on the die, to the PCB. After the wire bonds
are made, a rubbery or plastic material is placed over the silicon
die to give it some protection. Whereas the main chip is a large
DIP. You could not allow humans to handle the PCB, if the bond
wires were exposed :-) They'd crush the bond wires.
The machine uses a boost converter, and converts from
battery voltage to circuit voltage, with switching. And apparently,
there is a fair amount of ripple in the voltage. Maybe some of
the components are CMOS rather than NMOS.
https://www.hpmuseum.org/41int.jpg
https://www.hpmuseum.org/forum/thread-19379.html
The power switch would be in the battery portion of the circuit
(you can't leave the boost converter running constantly).
The boost converter has to work, in order for the machine
Bad switch
Bad battery (common with NiCd and reverse bias plate-out inside)
Bad boost converter
The kinds of conversion are things like "linear" (not efficient),
"buck converter" (efficient), "boost converter" (slightly less efficient,
does not usually have huge power output). In the old days, they did not
know how to multiply the voltage value all that effectively on their boost.
If you do voltage multiplication with diode trees, you only get
a "whiff" of current from the output. The higher the boost ratio,
the more wimpy the output. It's simpler to use an inverter with
all the voltage ratio provided by a transformer. There isn't a
lot of room for a transformer in a calculator. But it can be done.
A long time ago, they invented "planar magnetics" for the purpose.
The converter with the planar magnetics, the very first one,
could produce 60 amps. And it fit in the palm of my hand.
Those HP calc circuits had their fair share of quirks. It's a wonder
anyone got output from them :-) They have the smell of
"hobby circuit" about them. And a pretty low clock frequency.
They don't even need a quartz crystal, to generate the clock.

Interesting. I still have my HP16C and turn it on periodically to
amazement that it still works well.

[Zaidy036]

Post by Wendelin Uez
My pocket calculator HP41C can no longer switche on via on-of-key, even
not by removing batteries..
Does anyone know how to "repair" this feature?

If you use an iPhone there are emulators available in the app store