Electronics for me started as a hobby about 40 years ago. Then it became a
paying hobby (a job that was really fun). Now as my eyesight gets worse and
I have to work under at least a 3X magnifier just to see the parts, it has
become more drudgery. Used to also be fun to reverse engineer hardware by
tracing out and looking up standard chips to figure it out. Now standard
chips are in the minority and software and programmed PLDs/FPGAs predominate
making it near impossible.

I had to laugh at my wife's Pfaff. When she bought it (she is an avid
quilter) it had more computing power than my desktop computer.

Keep having fun - it keeps you young!
Oppie

"robb" wrote in message
...
Hi,

This repair is just for my own fun/hobby.

i thought it would just be a simple (resistor, diode, transistor) fried
component now that seems unlikely.

Yes, i was curious, so i did contact Pfaff about schematic and repair.
The
machine is old, new boards are not available since mid 90's. My local
authorized dealer will look at it for $80 with no guarantee and they
painted
a grim picture for it's repair ..... but did offer to recycle it for me
and
encouraged me to come look at there used and new machines.

i think its the over price the old equipment to push the new stuff

This repair is more of a for fun challenge/hobby for me .
I have *tinkered* with electronics since i was a teenager have a hobbyist
collection of electronic tools soldering irons/station, meters,
osciliscope
, solderless breadboards etc....

if i can not repair it i'll put it back together, it does some standard
stitches fine.... without the adjustment buttons the machine is about 1/4
as
useful but still useful.

thanks for all your help though , i mostly need some helpful
experience/guidance i think to solve this problem , what kinds of things i
need to do then i can figure out the doing part/

thanks again,
rob


"Oppie" wrote in message
...
The 75518 Qn outputs are a toem pole output for the VFD drive and go
between
Vcc2 (up to 170V) and ground. They are most likely using extra outputs
with
either diode coupling (to ignore source and only use sink output) or
voltage
scaling with the 12K resistor to get the scans to a compatible voltage.

Have you tried to contact Pfaff support? I have the manual for the 2010
but
it does not go into board level schematics (iirc) that was purchased
through
a Pfaff dealer. Never hurts to ask though. www.pfaff.com You might have
to
go through a dealer if Pfaff won't help you direct.
Oppie

"robb" wrote in message
...

"Oppie" wrote in message
...
Looks like a scanned switch matrix. If you look at one side of the
switch,
it should have a 1 of N scan where N is the number if scan lines. One
scan
line goes active at a time and selects a switch or VFD column. The
other
side of the switch is a sense that goes back somewhere else you do not
show.
The 40 pin chip you show is this one
http://focus.ti.com/docs/prod/folder...t/sn75518.html
Looks like it it giving the scans while you have two sense bits
returning
somewhere (the 12K resistors).


hello thanks for the help,

i had not gotten that far along, those 12K lines go back to main board,
i
was hoping the problem was isolated to this smll circuit board. *but*
now
i
am doubtfull ... i think the problem is on mainboard.

those 12k lines both return directly to the I1 and I0 pins of a
SN74LS251
found at

http://pdf1.alldatasheet.com/datashe...SN74LS251.html

an 8 input multiplexer w/3 state output, this chip sits near the bigg
IC's
on rhe main boad.

i am having trouble understand ing the VFD chip purpose in the button
presses ? th eVFD drives the VFD as wel as sharing with some button
pressing
fnction.

thnaks again for help ,
rob