Re: HP49G+ Turn-on Problem
On Apr 1, 4:11*pm, "John H Meyers" <jhmey...@nomail.invalid> wrote:[color=blue]
> On Tue, 01 Apr 2008 08:50:22 -0500, Bill Markwick wrote:
> Well, um, isn't the 50G built nearly identically to a 49G+?
Probably, but it would buy me about two years until the next failure.
For interest, here's my history of the decline and fall of HP quality:
1973: bought an HP45. It still works.
1996: bought an HP48GX. It was working fine when stolen in 2001.
2001: bought one of the last of the HP48GXs. In two years it began
locking up constantly from a memory problem.
2002: bought an HP49G. In two years it got the dreaded Turn-on
Problem, but this one was permanent.
2002: bought the last of the HP32SIIs. Though it still works, about
three times a year it will turn on with MEMORY CLEAR, for no evident
The current HP49G+ is a basket case, but I keep reviving it. A new
calc is at the top of the shopping list.
Re: HP49G+ Turn-on Problem
On Apr 1, 8:50*am, Bill Markwick <bd...@torfree.net> wrote:[color=blue]
> Just for reference, in case anyone has the same problem: my HP49G+
> started refusing to turn on unless I poked the reset contact 10 times
> or more, although once it started it was okay. *Another symptom was
> that the display contrast (ON +/-) had no effect, but the contrast
> would suddenly change itself back and forth.
> Aha, the display. *I pressed down on the bottom of the display and the
> calc began to turn on normally. *Problem solved, if awkwardly. *HP50G,
> here I come. *I might get up the nerve to open the 49G+ and see if I
> can fix it permanently, but for now, turn-on is a two-handed
> affair. :-)
I wonder if the HP49G+ (and the HP50) have the same hardware
construction as the original HP48S/X HP48G/GX series?
I've disassembled a couple of these lately, and it seems that over
time, the conductive paperlike printed circuit 'underlay' (which the
conductive keydomes contact) open circuits after a few years.
Also, the point of contact between this underlay and the main pcb,
which is done simply by pressure from the aforementioned paper-like
pcb simply becomes non-conductive over time; probably due to normal
environmental temperature and humidity fluctuations. This is the root
cause for the 'Pressing just below the display while pressing the 'ON'
key' method of powering up.
I've been considering designing a new/rugged keyboard underlay pcb
which would be soldered to the main board (the address lines going to
the keyboard are accessible). However, my main concern is how to get
the keyboard back together after disassembly. Also, I do not yet know
what the long term viability of the dome undersides conductivity.
I would appreciate others interest/experiences.