On 2007-09-09 07:47:44 -0700, "robb" said:
"Eeyore" wrote in message
...
robb wrote:
hello,
i am trying to repair a fault with an user interface circuit (UIC) board
and
control board out of an old 1987's computerized programmable Pfaff
sewing
machine (made in Western Germany).
a for fun project for me , a challenge 
programming consists of storing values in memory locations using keys
( +/-
buttons) on UIC board
PROBLEM : a group of 3 (+/-) *momentary switch* buttons on UIC board
used
to change memory values do not make any changes when pressed.
They're probably worn out.
Graham
hi,
thanks for reply and help.
is there a good way to test this ?
I would be convinced of that if they were all highly used keys... but
there are a total of 6 micro switches (for 3 buttons +/-) and they are not
typically all used with same frequency. One set is used most, one maybe
half that and the others very in-frequently as the nature of the values it
changes are not frequently used they are a convinience.
on the same board exists other buttons (same exact switch style) used more
frequently than these and they are still working ?? if that means anything
plus continuity tests just at switch connections to board shows changes as
as expected. The values may be no good but i get a continuity change that
matches with known working button/switches.
I am posting pics of the circuits on the binaries schematics page if that
will help ?
thanks again for your help ,
rob
I'd be pulling out a Logic Probe about now and checking what happens on
the lines to the switches. One of them at least should be pulsing (the
strobe). If the switches that do not work share the same Strobe or
Return line and no other switches do them your problem is either a bad
connection (most likely) or a failed driver on the strobe (next likely)
or damaged return gate.
Read up on digital troubleshooting, there are a number of books at
libraries that cover this and based on the period of construction for
this sewing machine one can hope they used off-the-shelf parts so it
will be easy to fix.
John :-#)#
--
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