23 Aug
2015
23 Aug
'15
1:28 a.m.
Howdy gents,
Working away on the recently acquired Osborne 1. Seems there's something
wrong with the KB - and if I didn't know better, I'd say it's a case of
shorted contacts.
The KB connector is 24 pins, double row header like a short floppy or IDE
header.
On the KB side, there are two "shorted" groups of pins. Group one is 2X
shortred pins, group two is 5X shorted pins.
Thing is, this KB is not really built to be serviced, best as I can tell.
The switch matrix is made of two layered flexible circuits, and the key
assys are 'riveted' in place, by melting over the plastic pins. So I see no
way to disassemble it and give it a clean.. and then, even so.
With such limited access, I don't see many avenues other than flushing with
solvent(s) and hoping for the best.
What's to be done? Is this one.. done already?
23 Aug
23 Aug
9:02 a.m.
On 23/08/2015 09:28, drlegendre . wrote:
Howdy gents,
Working away on the recently acquired Osborne 1. Seems there's something
wrong with the KB - and if I didn't know better, I'd say it's a case of
shorted contacts.
The KB connector is 24 pins, double row header like a short floppy or IDE
header.
On the KB side, there are two "shorted" groups of pins. Group one is 2X
shortred pins, group two is 5X shorted pins.
Thing is, this KB is not really built to be serviced, best as I can tell.
The switch matrix is made of two layered flexible circuits, and the key
assys are 'riveted' in place, by melting over the plastic pins. So I see no
way to disassemble it and give it a clean.. and then, even so.
With such limited access, I don't see many avenues other than flushing with
solvent(s) and hoping for the best.
What's to be done? Is this one.. done already?
I had a similar issue on a
Osborne a couple of weeks ago. I ended up
using a sharp knife to cut the melted pins on the rear of the keyboard
to remove the switches. Lifted the membrane and cleaned it before
refitting. To re-attach the switches, I used some super glue on the back
were each pin is and used a hot glue gun on the front in between each
switch.
Whole process took about an hour but has been working fine since. I
think this is caused by the cable constantly pressing down on the keys
when the keyboard is clipped to the front of the machine.
On an Osborne I repaired last year, just removing the the keyboard
assembly and giving a bit of a flex was enought to release the stuck key.
Cheers,
Dave
24 Aug
24 Aug
6:27 p.m.
On 08/23/2015 03:28 AM, drlegendre . wrote:
Howdy gents,
Working away on the recently acquired Osborne 1. Seems there's something
wrong with the KB - and if I didn't know better, I'd say it's a case of
shorted contacts.
The KB connector is 24 pins, double row header like a short floppy or IDE
header.
On the KB side, there are two "shorted" groups of pins. Group one is 2X
shortred pins, group two is 5X shorted pins.
I just prodded mine with a meter, and the only continuity I get is between
pins 2 and 23 (numbered as follows, looking into the keyboard connector,
with the cable exiting toward the right)
_____________________________________
| nc 02 03 04 05 06 07 08 09 10 nc nc |
| nc 14 15 16 17 18 19 20 21 22 23 nc |======
-------------------------------------
Thing is, this KB is not really built to be serviced,
best as I can tell.
Yeah, I just opened the case on mine, and it's a pretty nasty design -
cheap as possible :-( Wish I'd tried that keyboard on my system now so you
knew it had problems!
With such limited access, I don't see many avenues
other than flushing with
solvent(s) and hoping for the best.
Yeah, I'd do that first - or maybe soapy water followed by a flush with
distilled, then leave it for a week or so to dry. Can't hurt.
If that doesn't work... break the melted plastic bits off, take the thing
apart, clean the membrane. Reassemble and put blobs of glue where the
melted plastic bits were. If you have a drill press, counter-sink the holes
on the underside of the metal plate first; it'll give the glue more plastic
to adhere to.
If gluing doesn't work out... urgh. The switch bodies do seem to have a
little lip around the edges where they rest up against the membrane, so it
would be possible to slot metal bars down between the rows (secured at
either end somehow to the metal 'baseplate' below) in order to keep the
switches from falling out - but it would certainly be a bit of a project!
Nasty keyboard, though! I expect mine will go the same way at some point :/
cheers
Jules
7:13 p.m.
Hi Jules,
Oh, no worries - I'd have taken it in this condition whether or not you
were aware of the issues. After all, it +was+ a gift, and a very generous
one at that; not just in terms of materiel, but in terms of your time
spent, as well.
On the bright side, I may be able to send you some bootable media, if you
still need it. Another kind cctalk'er sent me a pair of bootable O1 discs,
one DBASEII and one WordStar.
I figure I'll go the solvent flush route, using tri-chlor, and see where
that goes. But honestly, I don't know what could be causing so many 'stuck'
keys on this thing! One would hope for (easily clear-able) contaminants,
but it might be more than that. As a previous poster noted, he felt it may
be due to the cord keeping several keys depressed during storage. That
might be worth investigating, if I can find a kb matrix map in the
(incomplete!) service docs.
As ever, my fear is that the materials won't withstand the solvent, even if
it's tri-chlor, and I'll end up washing away every hope of survival. Water
might be OK, but I'd have to grab a couple gals of distilled first.
Ultimately, the dreaded R&R is the option. Not sure if I have the
patience...
-L
On Mon, Aug 24, 2015 at 8:27 PM, Jules Richardson <
jules.richardson99 at gmail.com> wrote:
On 08/23/2015 03:28 AM, drlegendre . wrote:
Yeah, I just opened the case on mine, and it's a pretty nasty design -
cheap as possible :-( Wish I'd tried that keyboard on my system now so you
knew it had problems!
With such limited access, I don't see many avenues other than flushing with
> solvent(s) and hoping for the best.
Yeah, I'd do that first - or maybe soapy water followed by a flush with
distilled, then leave it for a week or so to dry. Can't hurt.
If that doesn't work... break the melted plastic bits off, take the thing
apart, clean the membrane. Reassemble and put blobs of glue where the
melted plastic bits were. If you have a drill press, counter-sink the holes
on the underside of the metal plate first; it'll give the glue more plastic
to adhere to.
If gluing doesn't work out... urgh. The switch bodies do seem to have a
little lip around the edges where they rest up against the membrane, so it
would be possible to slot metal bars down between the rows (secured at
either end somehow to the metal 'baseplate' below) in order to keep the
switches from falling out - but it would certainly be a bit of a project!
Nasty keyboard, though! I expect mine will go the same way at some point :/
cheers
Jules
Howdy gents,
Working away on the recently acquired Osborne 1. Seems there's something
wrong with the KB - and if I didn't know better, I'd say it's a case of
shorted contacts.
The KB connector is 24 pins, double row header like a short floppy or IDE
header.
On the KB side, there are two "shorted" groups of pins. Group one is 2X
shortred pins, group two is 5X shorted pins.
I just prodded mine with a meter, and the only continuity I get is between
pins 2 and 23 (numbered as follows, looking into the keyboard connector,
with the cable exiting toward the right)
_____________________________________
| nc 02 03 04 05 06 07 08 09 10 nc nc |
| nc 14 15 16 17 18 19 20 21 22 23 nc |======
-------------------------------------
Thing is, this KB is not really built to be serviced, best as I can tell.
25 Aug
25 Aug
4:52 a.m.
On 08/24/2015 09:13 PM, drlegendre . wrote:
On the bright side, I may be able to send you some
bootable media, if you
still need it.
Thanks for the offer, but I definitely have it somewhere - I'm just not
sure where! Eventually I'll have the PC set up to write images again anyway
(I'm just reorganizing my work/storage space at the moment so it's a bit of
a disaster area)
I figure I'll go the solvent flush route, using
tri-chlor, and see where
that goes. But honestly, I don't know what could be causing so many 'stuck'
keys on this thing!
Do any of the keys feel different? I assume there's a sponge pad on the
bottom of each key to produce the right feel when the key is pressed - I
wonder if something's been spilled in yours at some point, and some of
those pads have expanded and/or gone hard... although I suppose it could
just be age-related deterioration.
As ever, my fear is that the materials won't
withstand the solvent, even if
it's tri-chlor, and I'll end up washing away every hope of survival. Water
might be OK, but I'd have to grab a couple gals of distilled first.
Well, if there is sponge in there and it's gone bad then I suppose opening
the thing up is the only solution anyway :(
Ultimately, the dreaded R&R is the option. Not
sure if I have the
patience...
Yup, it'd certainly be a job. Unfortunately I don't have the contact info
for the guy who took the third one of these machines, but I suppose he may
surface on the list at some point. It's possible that machine was snafu in
such a way that there might be a surplus keyboard available...
cheers
Jules
11:25 a.m.
I'll admit to being surprised at the cheapness of the keyboard. Here I
expected to find a true mechanical type, like the early IBM machines - what
I found is a step-down from the C-64.
The switching side is what I'd term a 'membrane sandwich. There are three
layers in the stack, with upper & lower layers forming the switch contact
pairs. Sandwiched in the middle is a perforated insulator sheet, with a
hole pattern that matches the switch contact pattern. Pressing on the right
area of the stack unites the upper & lower contacts, temporarily closing
the switch.
So I suppose if a spilled liquid infiltrated the stack, perhaps drying and
leaving a residue, it may have short-circuited any number of contact pads.
But IIRC, I was measuring +very+ low resistance in the shorted pins. I'm
not sure how even dried Coca-Cola could create that hard of a short.. so I
need to take some more careful readings. If they are truly hard-shorted,
I'd tend to look for something other than a contamination issue.
On Tue, Aug 25, 2015 at 6:52 AM, Jules Richardson <
jules.richardson99 at gmail.com> wrote:
On 08/24/2015 09:13 PM, drlegendre . wrote:
On the bright side, I may be able to send you
some bootable media, if you
still need it.
Thanks for the offer, but I definitely have it somewhere - I'm just not
sure where! Eventually I'll have the PC set up to write images again anyway
(I'm just reorganizing my work/storage space at the moment so it's a bit of
a disaster area)
I figure I'll go the solvent flush route, using tri-chlor, and see where
that goes. But honestly, I don't know what
could be causing so many
'stuck'
keys on this thing!
Do any of the keys feel different? I assume there's a sponge pad on the
bottom of each key to produce the right feel when the key is pressed - I
wonder if something's been spilled in yours at some point, and some of
those pads have expanded and/or gone hard... although I suppose it could
just be age-related deterioration.
As ever, my fear is that the materials won't withstand the solvent, even if
it's tri-chlor, and I'll end up washing
away every hope of survival. Water
might be OK, but I'd have to grab a couple gals of distilled first.
Well, if there is sponge in there and it's gone bad then I suppose opening
the thing up is the only solution anyway :(
Ultimately, the dreaded R&R is the option. Not sure if I have the
patience...
Yup, it'd certainly be a job. Unfortunately I don't have the contact info
for the guy who took the third one of these machines, but I suppose he may
surface on the list at some point. It's possible that machine was snafu in
such a way that there might be a surplus keyboard available...
cheers
Jules
12:06 p.m.
I'll admit to being surprised at the cheapness of the keyboard. Here I
expected to find a true mechanical type, like the early IBM machines - what
I found is a step-down from the C-64.
Depends one what you mean by 'early IBM machine'. The well-known type M
used on the 5170 PC/AT [1] is of this sort of design
[1] Yes I am well aware that the 5170 is not an early IBM machine in terms of IBMs
total computer production. But a lot of people now think it is ancient.
The switching side is what I'd term a 'membrane sandwich. There are three
layers in the stack, with upper & lower layers forming the switch contact
pairs. Sandwiched in the middle is a perforated insulator sheet, with a
hole pattern that matches the switch contact pattern. Pressing on the right
area of the stack unites the upper & lower contacts, temporarily closing
the switch.
Another well-known keyboard with this type of design is the DEC LK201 (as used on
the VT220, etc).
I have taken both LK201s and IBM type Ms totally apart. The latter I managed to
reassemble with screws. The former I never managed to get to work properly again,
the plastic is just too thin to take screws, there is not enough to re-melt and no glue
seemed to hold.
So I suppose if a spilled liquid infiltrated the
stack, perhaps drying and
leaving a residue, it may have short-circuited any number of contact pads.
But IIRC, I was measuring +very+ low resistance in the shorted pins. I'm
not sure how even dried Coca-Cola could create that hard of a short.. so I
need to take some more careful readings. If they are truly hard-shorted,
I'd tend to look for something other than a contamination issue.
What bothers me about this design it that it relies on the the springiness of the
plastic to open the contacts again. This seems like something that might fail with
time so the sheets remain in contact.
-tony
3411
days inactive
3413
days old
6 comments
4 participants
participants (4)
-
ard＠p850ug1.demon.co.uk -
dave＠willomail.co.uk -
drlegendre＠gmail.com -
jules.richardson99＠gmail.com