Hello John Marchant, on 14-Oct-98 12:43:54, you said,
>Does anyone now if the keyboards for the A3000 and 4000 are the same
>electrically?
They are identical in every way with exception of the coil cord's plug
(the big box end). You can swap cables between an A3000 and an A4000
without a problem.
>I have both machines and the keyboards look exactly the same except the
>3000 kbd has a round plug body. Internally, the construction is rather
>different: but then CBM used various designs over the years.
The A3000 and the A4000 keyboard PCB should have a small cream colored
four pin header where the coil cord attaches internally to the keyboard.
Is this not the case then?
>The reason I ask is that my A3000 keybd, bought 3rd hand 18 months ago,
>is rather erratic and has many of the tiny screws missing: and though I
>can clean it out & keep it working, I'd like to find a good replacement.
>I need to know if I can accept one from or for either machine.
If you'd substitute an A4000 coil cord for use with an A3000, chances are
any adapter (PS/2 to AT) would ultimately be too shallow and not maintain
an adequate connection.
>I have no manuals for the 3000, so I can't RTFM for pinouts :-)
Well, here's a DIY sorta FAQ on keyboard repair; maybe it'll help.
KEYBOARD TROUBLE-SHOOTING FAQ (29 AUGUST 1998, REV 4)
=====================================================
I thought I should do sorta a DIY (Do it Yourself) text file on simple, yet
problematic keys/keyboard repair tips.
A. TWO KINDS OF A2000 KEYBOARD
1. Pop off a keycap --- if the piece of plastic underneath is
a. SQUARE, then it's an old style A500/A2000 keyboard.
b. ROUND, then it's a modern A2000/A3000/A4000 keyboard.
B. TWO KINDS OF ROUND PLUNGER PIECES UNDER THE KEYCAP (re: 1.b. above)
1. If the round plunger under the keycap has
a. no inner "lip" on top of it, it's from an A3000 keyboard, an
A4000 keyboard, or one of the last production runs of the A2000
keyboards.
1. Only A3000 or A4000 keyboards can be used for salvaging this
type of piece (or a late production run from the A2000
keyboard series).
b. an inner "lip" or ridge on top of it, it's from an A500/A2000
keyboard.
1. You can use A500/A2000 keyboards for the purpose of canni-
balization for this type; A C-128 keyboard can also be used as
a source of parts. The keycaps can't, but the the plungers,
springs, and carbon-impregnated rubber contact are identical.
C. REPAIR/FIXES FOR OLD STYLE A2000 KEYBOARDS WITH PROBLEMATIC KEYS (re:
1.a. above)
1. Remove the square plastic piece underneath the keycap. Remove the
spring underneath that. Stretch the spring somewhat, as over time
it gets compressed from heavy usage.
2. Put the spring and square piece of plastic back on, leaving the
keycap off. Watch and observe as you press the square piece of
plastic down. There are two metal arms separated from each other
by a narrow plastic bridge on the square plastic piece. If they
make full contact on a keypress all is well. If not, remove the
square piece and the spring again. Bend/arc the arms towards
each other, making sure they're not slanted in either direction
when done. Check a properly working key next to it for reference
orientation if need be. Put it all back together, including the
keycap. Give it a press. All should be OK.
D. REPAIR/FIXES FOR MODERN A2000/A3000/A4000 KEYBOARDS WITH PROBLEMATIC
KEYS (re: 1.b. above)
1. If you have access to a multimeter or something that can measure
ohms, take a reading from the black graphite rubberized contact
found on the underside of the keyboard. A good rule of thumb to
follow is if it provides more than 250 ohms, remove and replace it.
As a keyboard ages and some of the graphite-impregnated compound
wears off, ohm values increase, leading to a non-responsive key.
You _can_ use contacts that have a greater value than this figure,
but use it as a guideline --- I cannot give concrete range values.
Follow D2 for specifics on replacement (it'd be wise to take a pre-
reading of the replacement contact via a multimeter prior to
installation).. If you do not have access to a multimeter, follow
D2 anyway (as this explanation is being provided for the technical-
minded; your non-functioning keys do not necessarily have to be
measured in order for you to fix them so long as you consult this
guide and realize you may have to replace the contact several times
until one providing sufficient ohm resistance is found).
2. Remove all twenty-some screws from the backside of the inner
keyboard PCB. Find the offending key and remove the plunger from
the bottom side with a small screwdriver. You should see a small
rubber graphite impregnated piece from this side of the keyboard.
It's secured by a "pincher" type of retainer. You can either
replace the entire round cylinder along with the black piece from
another A500 keyboard or simply remove and replace the black piece
from your spare for-parts keyboard. Reassemble the entire thing, but
don't put all the screws in place. Boot your machine and test the
offending key. You should see the previous problem you had
disappear. If not, remove what screws you have reinstalled and
replace the offending black piece with another one until it does
work again.
E. HELP!!! I HAVE ````````````````````` ON THE SCREEN WITH MY KEYBOARD!
1. One of three likely problems: cold solder joint, problematic
cable (what goes from the keyboard to the Amiga itself), or
borderline MPU (the keyboard's main chip, the "brain"). The last of
the three known causes is the likeliest, but I have seen either of
the other two create this identical effect.
2. Check all solder joints and retouch any that seem to need it.
3. Try a cable from another A2000 (take note of the cable's plug end
that attaches to the PCB; older A2ks have a large black connector
with six holes and five wires; modern A2ks/A3ks/A4ks have a small
white connector with four holes and four wires).
4. If no success, it's likely to be an MPU problem. This is the
large chip inside your keyboard. Desolder and replace at your
own peril. Also, I recommend SOCKETING this chip, to make future
replacement far easier. Consult Radio Shack for a proper fitting
socket (that's where I got'em from).
F. MY KEYBOARD DOESN'T ALLOW MY MACHINE TO BOOT AND THE LED IS HALF-BRIGHT!
1. I have two keyboards this way. Check all the small components for
any visible sign of damage. Replace any you find.
2. Replace the MPU. NOTE: I've not attempted this fix, but more than
likely the MPU's crashed and would be the problem.
[sidenote: I have several of the MPU chips here if someone would like
to obtain one. I'll supply it *provided* you email and confirm or deny
your success as to this being the problem and solution after attempting
the repair]
G. BUT I HAVE AN A3000 AND ONLY AN A500/A2000 KEYBOARD SPARE FOR PARTS!
[OR VICE VERSA]
1. There are a couple ways you can handle this situation:
a. You could remove the black rubber graphite contact from the
bottom of the plunger ONLY and simply replace the bad one on your
A3000.
b. If your A3000 keycap itself is bad, remove the entire keycap,
plunger, and contact. Remove the identical components from your
spare A500/A2000 keyboard. Drop in and replace, as the plunger
and keycap will match each other in this case.
There are more suggestions and solutions I've found, but thought I should
share the basic knowledge with the Amiga community. Any inquiries or
additions, feel free to contact me via the address below. You will get
credit for any user-provided additions or clarifications as warranted.
BLATANT SELF-PLUG/PROMOTIONALISM
--------------------------------
I do free-lance repair jobs if I'm capable of it (being I have the time
provided, and the problem isn't likely the MPU [I'm not the proficient
solder I often pretend to be, and don't want to potentially ruin your
keyboard by working on it at 5a.m. after being up 18 hours :-] Consult my
other post that frequently appears in c.s.a.m. for details on my repair
offer.
SEEKING ASSISTANCE BY AMIGAGUIDERS
----------------------------------
I would very much like to convert this to an AmigaGuide-compliant document.
If anyone's up to the task, please email me. I can include some detailed
scans (created via my Paragon SPII scanner) as a reference for within the
document (like A2k/a3k/a4k keyboard connectors, keycap stems, and the
like). You would receive co-credit and the resulting document would be
uploaded to aminet after a thorough going over to verify the document's
integrity and proper syntax (amigaguide-related).
ACKNOWLEDGMENTS
---------------
Credit goes to Brian Heyboer <bjheyb...@space.honeywell.com> for the C128
keyboard compatibility note.
Credit goes to Jeffrey W. Grzanich (grzan...@prismnet.com) for the ohm
explanation and guideline figures.
DISCLAIMER
----------
Some of these repairs are NOT for the feint of heart and in no way shall I
be held responsible for the work you undertake yourself. If you're not
comfortable doing it, DON'T DO IT! 'Nuff said :P
> John
>--
>John Marchant ('Gnome'). Bedford UK. gn...@enterprise.net
>Amiga 4000/40, A3000/30, A500 Fidonet 2:257/137.16
>"Keyboard": An instrument used for entering errors into a system
>* Pick-Tag v2.5 *
--
...
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