Re: Apple ][+ keyboard problem, please help!

[Rubywand <rubywand@swbell.net>]

> Vince Briel writes ...
> 
> I'm leaning towards the bad incoder since I already reseated the controller
> board and encoder a couple of times.  I got an email reguarding this stating
> someone from a school who had same problem in past and he said static
> electricity travels through keyboard from hands and damages encoder chip!  I
> believe that this is possible, but I'm thinking it was just its time.

     If you are in a static-prone environment-- like, you notice little sparks
hopping from your fingers when turning on the lights, etc.-- then zapping IC's
by touch is a hazard. I do not know how likely you would be to damage a KB
controller line by touching a key.

     Evidently, the A, S, 1, 2, SPC, and CR keys are on the same line. This is
something you can probably verify visually by viewing traces on the KB matrix.
One way or another, you need to locate the trace which joins just the defective
keys and goes to some pin on the KB controller IC.

     Since the keys do not work, the line has probably either become
disconnected from the controller or the controller has developed a defect at
the input or output which goes the trace connecting the keys.

Some kind of short of the line to +5 or GND-- e.g. from a wire shard, Coke
spill, etc.-- is another possibility. But, since the failure developed 'out of
the blue', an external short seems less likely than a break or controller
defect.

     To check for a break, you need to locate and mark (like with white-out)
the KB controller pin which is supposed to be connected to the trace connecting
the six bad keys. Then, you can use an Ohmmeter to check for continuity from
the actual IC pin to the trace. (Setting the meter to Rx100 is a way to reduce
the max current which can flow through the circuit being checked while,
usually, avoiding going to a higher test voltage.)

     If you find no connection, check the pins on either side (you could be off
by a pin).  If there is definitely no good connection from the pin to the
trace, some suspects are ... a dirty pin making poor contact in the socket, a
break inside the socket from the pin contacts to the part soldered to the
circuit board, a fractured solder connection where the socket pin is soldered,
a break between the solder point and the trace. (And, if the IC was pulled and
reinserted, there is a chance the pin got bent up under the IC.)

     If the connection is okay, closely inspect the socket (especially between
the socket and circuit board) for any bits of wire or solder or gunk near the
pin. If there are any wires on the matrix, check for placement which could
cause one to get pressed against a sharp point on some contact point. You might
try some checks of R from the trace to +5 and GND. If you find a low R, this
could indicate a short somewhere (other than a short due to a blown IC line).

     If the connection from the KB controller pin to the trace connecting the
six keys is okay and nothing seems to be causing a short, try plugging in the
KB and turning On the computer. If the keys still do not work, the odds of a
defective KB controller are pretty high.



Rubywand