[robb]

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.

the UIC board has a VFD output display (16 chars) and 12 input buttons and 5
indicator LEDs. All but 3 of the buttons register presses correctly. the 3
broken buttons seem to be individually ok as i get continuity changes when i
test with multimeter and push buttons.

this UIC board is connected to the control board via 12 conductor ribbon ???

I am not sure what kind of things to do to isolate trouble ........

i have dome visual inspection of solder joints and components with no
obvious issues.

How would the VFD display values , LED indicatiors and inputing buttons be
managed through a 12 conductor ribbon ??? in 1980's style ?? how to trace ot
monitor value changes.

Any troubleshooting or tracing ideas advice would br greatly appreciated.

thanks,
rob

[Tom Biasi]

"robb" wrote in message
...
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.

the UIC board has a VFD output display (16 chars) and 12 input buttons and
5
indicator LEDs. All but 3 of the buttons register presses correctly. the 3
broken buttons seem to be individually ok as i get continuity changes when
i
test with multimeter and push buttons.

this UIC board is connected to the control board via 12 conductor ribbon
???

I am not sure what kind of things to do to isolate trouble ........

i have dome visual inspection of solder joints and components with no
obvious issues.

How would the VFD display values , LED indicatiors and inputing buttons be
managed through a 12 conductor ribbon ??? in 1980's style ?? how to trace
ot
monitor value changes.

Any troubleshooting or tracing ideas advice would br greatly appreciated.

thanks,
rob




Well without seeing the circuit I could only guess that they used RAS and
CAS to address the keypad matrix. (Row Address and Column Address).

The ribbon cable is a place to look but the addressing logic could be bad.

Tom

[Eeyore]

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

[robb]

"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

[robb]

"Tom Biasi" wrote in message
...

"robb" wrote in message
...
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


Well without seeing the circuit I could only guess that they used RAS and
CAS to address the keypad matrix. (Row Address and Column Address).

The ribbon cable is a place to look but the addressing logic could be bad.

Tom


hi Tom,

thanks for the reply and ideas.
i have posted some circuit pics on the

"alt.binaries.schematics.electronic"

if that would help formulate some ideas

thanks for your help ideas and time,
rob

[robb]

hello,

i posted some circuit board pics on the

"alt.binaries.schematics.electronic"

under topic ---- "pfaff UIC circuit board" to

if that will help formulate some ideas on how to repair.

thanks for any help,
rob

"robb" wrote in message
...
hello,

[Anthony Fremont[_3_]]

Eeyore wrote:
robb wrote:

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.

All three of them at the same time?......yeah. Besides, he said he tested
them already with a multimeter.

[Spehro Pefhany]

On Sun, 9 Sep 2007 10:01:00 -0400, the renowned "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.

the UIC board has a VFD output display (16 chars) and 12 input buttons and 5
indicator LEDs. All but 3 of the buttons register presses correctly. the 3
broken buttons seem to be individually ok as i get continuity changes when i
test with multimeter and push buttons.

this UIC board is connected to the control board via 12 conductor ribbon ???

I am not sure what kind of things to do to isolate trouble ........

i have dome visual inspection of solder joints and components with no
obvious issues.

How would the VFD display values , LED indicatiors and inputing buttons be
managed through a 12 conductor ribbon ??? in 1980's style ?? how to trace ot
monitor value changes.

Any troubleshooting or tracing ideas advice would br greatly appreciated.

thanks,
rob

What else is on the display board (part numbers)? Ca. 1987, it's
probably not a dedicated micro, but there's something else active
there to keep the number of wires down. I'm guessing it's probably a
mechanical issue on the display/key PCB (broken trace, broken wire in
the flat cable). I'd pay particular attention to the flat cable wires
(test them) and the traces going to the switches.

PCB technology isn't/wasn't always 100% reliable, especially back
then, and it's also possible that a via has cracked and is
electrically open.


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

[robb]

"robb" wrote in message
...
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).


the machine is a Pfaff 1471 (1987 is the approx imate year it was made )

in case the year makes a difference on advice

rob

[DaveM]

"robb" wrote in message
...
hello,

i posted some circuit board pics on the

"alt.binaries.schematics.electronic"

under topic ---- "pfaff UIC circuit board" to

if that will help formulate some ideas on how to repair.

thanks for any help,
rob

"robb" wrote in message
...
hello,



The way I would attack this problem would be:
Use your ohmmeter to trace the common connections from the switches to the
ribbon cable, then make sure that you have continuity through the ribbon cable.
From there, trace the circuit to whatever component(s) they connect to.
As another poster mentioned, they might be strobed using a CAS/RAS technique.
If either signal is missing, then the circuit won't respond to set of switches.
It's pretty much useless to attempt to troubleshoot your problem using the
pictures you posted. You really need to get into the circuit with your ohmmeter
and trace the circuitry. Draw a rudimentary diagram of your tracing. See
You can also power up the boards and look at the switches with a scope. You
will probably see pulses on one side of the switches. Press one of them and
trace the resulting signal back through the circuit and see where it goes away.
You'll have to find data sheets on the ICs involved, so plan on doing some
Googling. Search for the part number of the part, and datasheet. Like this:
7401 datasheet

That should get you in the ballpark.

Cheers!!!
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

"In theory, there isn't any difference between theory and practice. In
practice, there is." - Yogi Berra

[Jamie]

Eeyore wrote:

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

THat's just like you Mr. Ham. Open up before you read the rest of his
post! or did you do that intentionally? He stated that these 3 buttons
were tested via an ohm meter and appear to be working.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

[Jamie]

robb wrote:

"robb" wrote in message
...

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).



the machine is a Pfaff 1471 (1987 is the approx imate year it was made )

in case the year makes a difference on advice

rob



You know you have already stated that you tested the buttons with an ohm
meter how ever, did you test them down on the ribbon cable end that goes
into the processor?
it most likely is a RAS/CAS system where is, one wire in the ribbon
connects with another..
you should vie the scan lines from Uc that run to the keyboard and
start looking for a pair of lines that come together with the ohm meter
as you press the bad keys.
if you do get action on all the bad keys when testing it at the Uc
(microchip), then you have something wrong with the Uc ..
other wise, if you don't get closing action, then, work your way back
to the ribbon header or what ever up to the keyboard it self.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

[Michael A. Terrell]

Anthony Fremont wrote:

Eeyore wrote:
robb wrote:

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.

All three of them at the same time?......yeah. Besides, he said he tested
them already with a multimeter.


Never trust a demented donkey for repair advise.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

[Radiosrfun]

"Michael A. Terrell" wrote in message
...
Anthony Fremont wrote:

Eeyore wrote:
robb wrote:

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.

All three of them at the same time?......yeah. Besides, he said he
tested
them already with a multimeter.


Never trust a demented donkey for repair advise.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Isn't the title of this thread a bit misleading and unfair? It's not "all"
brits - just one!

[Michael A. Terrell]

Radiosrfun wrote:

"Michael A. Terrell" wrote in message
...
Anthony Fremont wrote:

Eeyore wrote:
robb wrote:

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.

All three of them at the same time?......yeah. Besides, he said he
tested
them already with a multimeter.


Never trust a demented donkey for repair advise.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Isn't the title of this thread a bit misleading and unfair? It's not "all"
brits - just one!

I agree, but I wasn't the one who changed the name. It was Anthony
Fremont.

OTOH, anything posted by the donkey makes his country look bad. Maybe
they need to send him to the glue factory?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

[Radiosrfun]

"Michael A. Terrell" wrote in message
...
Radiosrfun wrote:

"Michael A. Terrell" wrote in message
...
Anthony Fremont wrote:

Eeyore wrote:
robb wrote:

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.

All three of them at the same time?......yeah. Besides, he said he
tested
them already with a multimeter.


Never trust a demented donkey for repair advise.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Isn't the title of this thread a bit misleading and unfair? It's not
"all"
brits - just one!

I agree, but I wasn't the one who changed the name. It was Anthony
Fremont.

OTOH, anything posted by the donkey makes his country look bad. Maybe
they need to send him to the glue factory?


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

I "used" to give him some credit in the past - waited to see where he was
coming from - or going to...... I'm curious - does he perhaps have a twin -
we know about from elsewhere? I don't think I need to mention the name to
you Michael.

I had a very brief chat (on yahoo) with another Brit who shall we say -wears
the same shoes - a nut case. Well, I guess they have their share, we have
ours.
Maybe if we find them all through chatting, we can help the Authorities
round them all up.

[Don Bowey]

On 9/9/07 12:09 PM, in article , "robb"
wrote:


"robb" wrote in message
...
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).


the machine is a Pfaff 1471 (1987 is the approx imate year it was made )

in case the year makes a difference on advice

rob




The only thing that will make a difference is you posting a schematic.

[robb]

"Don Bowey" wrote in message
...
On 9/9/07 12:09 PM, in article , "robb"
wrote:

The only thing that will make a difference is you posting a schematic.

well if i had a schematic i would surely post it instead of circuit board
pictures.

i was hoping some one might notice the chips used and there configuration
and maybe have an idea about how and what to look for.

thanks for help ,
rob

[legg]

On Sun, 9 Sep 2007 10:01:00 -0400, "robb" wrote:


the UIC board has a VFD output display (16 chars) and 12 input buttons and 5
indicator LEDs. All but 3 of the buttons register presses correctly. the 3
broken buttons seem to be individually ok as i get continuity changes when i
test with multimeter and push buttons.

this UIC board is connected to the control board via 12 conductor ribbon ???

Three switches will not all have failed. This suggests connectivity
or fault on a common line being shared.

Locate the common connection for the three switches, using simple
continuity. At the same time check the other switches to see if groups
share the same pattern of grouped continuity.

You should be able to follow tracks with good continuity from working
switches, to get an idea where the trace for the bad row should route.
When these no longer correspond, you've located a potential location
to search for the fault.

If all group traces reach semiconductor pins successfully, then the
first semiconductor the group hits is suspect. IO devices in machines
with motor controls can suffer problems over time. These may be fairly
simple and common devices (for that day), interfacing to more complex
or application-specific devices.

I don't see solder-side tracking for the main board in viscinity of
the connector in question. Those are a small number of wires in that
harness, to handle both keyboard and display, so it may not be
involved at all.

RL

[Don Bowey]

On 9/9/07 5:00 PM, in article , "robb"
wrote:

"Don Bowey" wrote in message
...
On 9/9/07 12:09 PM, in article , "robb"
wrote:

The only thing that will make a difference is you posting a schematic.

well if i had a schematic i would surely post it instead of circuit board
pictures.

i was hoping some one might notice the chips used and there configuration
and maybe have an idea about how and what to look for.

thanks for help ,
rob




you could make a list of the Ics on the board and download all the
datasheets for them. That should help you.

[robb]

wow thanks legg,

i guess alot of detective information is allready there in the fault
description that i ignored.

namely a group of buttons have all failed yet other groups of buttons with
different functions has not failed on the same board should lead one to
suspect a possible common shared connection between these three failed
buttons.

so look to the common connection point for all three failed buttons.

how simple and forthright yet elusive to amateurs like me.

one interesting thing i noticed is one of the alphanumeric LED cells has
artifacts (slight glowing) displayed in it and the artifacts shimmer and
change slightly when a BAD buton is pushed could this indicate a failure of
some component ?

thanks... i will look as you suggested,the Balance key, Stitch length
key and Stitch width key are the only buttons that do not seem to
work.

The programming keys (ie. stitch selector buttons) do work as do all
other buttons including the top right key that shows optimal settings
and recommended foot. The machine will stitch the correct stitch
according to parameters in the display for the selected stitch (eg.
stitch 00 straight stitch at 2.5 length *and* stitch 10 zig zag at
3.0 wide 2.0 length and so on)

*problem* being that i can not change the Balance nor Stitch length
nor Stitch width for any of the stitch selections 00-99 ??? when a
number appears above the keys, then some stitches have the amber
light and does not chnage those as expected.

I tried erasing memory as you said (no luck). I tried removing and
installing new batteries (no luck).


rob

"legg" wrote in message
...
On Sun, 9 Sep 2007 10:01:00 -0400, "robb" wrote:


the UIC board has a VFD output display (16 chars) and 12 input buttons
and 5
indicator LEDs. All but 3 of the buttons register presses correctly. the
3
broken buttons seem to be individually ok as i get continuity changes
when i
test with multimeter and push buttons.

this UIC board is connected to the control board via 12 conductor ribbon
???

Three switches will not all have failed. This suggests connectivity
or fault on a common line being shared.

Locate the common connection for the three switches, using simple
continuity. At the same time check the other switches to see if groups
share the same pattern of grouped continuity.

You should be able to follow tracks with good continuity from working
switches, to get an idea where the trace for the bad row should route.
When these no longer correspond, you've located a potential location
to search for the fault.

If all group traces reach semiconductor pins successfully, then the
first semiconductor the group hits is suspect. IO devices in machines
with motor controls can suffer problems over time. These may be fairly
simple and common devices (for that day), interfacing to more complex
or application-specific devices.

I don't see solder-side tracking for the main board in viscinity of
the connector in question. Those are a small number of wires in that
harness, to handle both keyboard and display, so it may not be
involved at all.

RL

[James Sweet]

"robb" wrote in message
...
wow thanks legg,

i guess alot of detective information is allready there in the fault
description that i ignored.

namely a group of buttons have all failed yet other groups of buttons with
different functions has not failed on the same board should lead one to
suspect a possible common shared connection between these three failed
buttons.

so look to the common connection point for all three failed buttons.

how simple and forthright yet elusive to amateurs like me.

one interesting thing i noticed is one of the alphanumeric LED cells has
artifacts (slight glowing) displayed in it and the artifacts shimmer and
change slightly when a BAD buton is pushed could this indicate a failure
of
some component ?


Sounds like there might be a missing ground, which would cause current to
flow down paths it shouldn't. It's common for problems like this to be
caused by cold solder joints or hairline fractures in circuit boards, I'd
start by touching up any suspect joints.

[Anthony Fremont[_3_]]

Radiosrfun wrote:

Isn't the title of this thread a bit misleading and unfair? It's not
"all" brits - just one!

I know that, of course, but I have to play it the "dumb ass" way and lump
everyone into one group. ;-)

[Lostgallifreyan]

Might as well throw my bit in too.

Forget diagnostics, just treat the most likely symptom; it's a harmless
excercise, and if it fails you can start doing tests.

Start by assuming that pressure on switches has caused a stress fracture in
one of the address lines, so find the track common to the failed switch
group, then remove solder from the first switch terminal that track arrives
at, and use a scriber to scratch the solder resist back along the track
about 3 to 5 mm, then reapply solder.

If that doesn't fix it, start testing stuff, starting with a resistance
(not continuiuty) test of that address line's track back to source.

[Lostgallifreyan]

"James Sweet" wrote in
news:2B1Fi.3192$qV3.2218@trndny02:

one interesting thing i noticed is one of the alphanumeric LED cells
has artifacts (slight glowing) displayed in it and the artifacts
shimmer and change slightly when a BAD buton is pushed could this
indicate a failure of
some component ?


Sounds like there might be a missing ground, which would cause current
to flow down paths it shouldn't. It's common for problems like this to
be caused by cold solder joints or hairline fractures in circuit
boards, I'd start by touching up any suspect joints.


Exactly. As well as what I said in my other post, look for other possible
stress points like the one by the failed switch group, there might be more
about to fail, and reworking the connections is far easier and faster than
doing elaborate diagnostics which you might never have to do.

[Ron(UK)]

Radiosrfun wrote:
"Michael A. Terrell" wrote in message
...
Anthony Fremont wrote:
Eeyore wrote:
robb wrote:
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.
All three of them at the same time?......yeah. Besides, he said he
tested
them already with a multimeter.

Never trust a demented donkey for repair advise.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Isn't the title of this thread a bit misleading and unfair? It's not "all"
brits - just one!



That's just typical of Americans, they ALL generalise!
--- please note


Ron

[Radiosrfun]

"Anthony Fremont" wrote in message
...
Radiosrfun wrote:

Isn't the title of this thread a bit misleading and unfair? It's not
"all" brits - just one!

I know that, of course, but I have to play it the "dumb ass" way and lump
everyone into one group. ;-)


Ah, ok........... I get your point......

[robb]

"Don Bowey" wrote in message
...
On 9/9/07 5:00 PM, in article , "robb"
wrote:

"Don Bowey" wrote in message
...
On 9/9/07 12:09 PM, in article ,
"robb"
wrote:

The only thing that will make a difference is you posting a schematic.

well if i had a schematic i would surely post it instead of circuit
board
pictures.

i was hoping some one might notice the chips used and there
configuration
and maybe have an idea about how and what to look for.

thanks for help ,
rob


you could make a list of the Ics on the board and download all the
datasheets for them. That should help you.

Hey Don,
I realize i am not even an electronic hobbyist more like a "dangerous
adventurere" at best when it comes to repairing electronics (i have
succesfully stripped 10 guage wire and i can distinguish resistor from
diodes most of the time)

but, how would looking up all the IC datasheets help ?

would it not be more efficient to concentrate only on the ICs directly
connected to the suspect components ?

thanks for your time,
rob

[Radiosrfun]

"robb" wrote in message
...

"Don Bowey" wrote in message
...
On 9/9/07 5:00 PM, in article , "robb"
wrote:

"Don Bowey" wrote in message
...
On 9/9/07 12:09 PM, in article ,
"robb"
wrote:

The only thing that will make a difference is you posting a schematic.

well if i had a schematic i would surely post it instead of circuit
board
pictures.

i was hoping some one might notice the chips used and there
configuration
and maybe have an idea about how and what to look for.

thanks for help ,
rob


you could make a list of the Ics on the board and download all the
datasheets for them. That should help you.

Hey Don,
I realize i am not even an electronic hobbyist more like a "dangerous
adventurere" at best when it comes to repairing electronics (i have
succesfully stripped 10 guage wire and i can distinguish resistor from
diodes most of the time)

but, how would looking up all the IC datasheets help ?

would it not be more efficient to concentrate only on the ICs directly
connected to the suspect components ?

thanks for your time,
rob




If you look up the "Data sheets" of those ICs - you can see what their
actions are "supposed" to be - and see if anything is failing to do it's
particular job. You can analyze the outside parts all you want - if a Chip
is failing - you won't know it without the data sheet and way to check it
for input/output. If you have an "input" signal to one of the chips - but no
output - then it isn't working. Not being able to understand the action of
those chips on that board - can leave you scratching your head a while - and
maybe running in circles looking. Checking all the traces, switches,
whatever - isn't a bad thing - but it won't uncover a dead IC - especially
if you have tunnel vision - not wanting to accept it "may" be a chip. I'm
not suggesting it "is" a chip - but the suggestion offered couldn't hurt.
You will have a much better understanding of the "intended" performance of
the circuit. Chips "can" go bad.

[Arfa Daily]

"Lostgallifreyan" wrote in message
...
Might as well throw my bit in too.

Forget diagnostics, just treat the most likely symptom; it's a harmless
excercise, and if it fails you can start doing tests.

Are you a medical doctor by any chance ... ? ;~)

Arfa

[Arfa Daily]

"Radiosrfun" wrote in message
...
"robb" wrote in message
...

"Don Bowey" wrote in message
...
On 9/9/07 5:00 PM, in article , "robb"
wrote:

"Don Bowey" wrote in message
...
On 9/9/07 12:09 PM, in article ,
"robb"
wrote:

The only thing that will make a difference is you posting a
schematic.

well if i had a schematic i would surely post it instead of circuit
board
pictures.

i was hoping some one might notice the chips used and there
configuration
and maybe have an idea about how and what to look for.

thanks for help ,
rob


you could make a list of the Ics on the board and download all the
datasheets for them. That should help you.

Hey Don,
I realize i am not even an electronic hobbyist more like a "dangerous
adventurere" at best when it comes to repairing electronics (i have
succesfully stripped 10 guage wire and i can distinguish resistor from
diodes most of the time)

but, how would looking up all the IC datasheets help ?

would it not be more efficient to concentrate only on the ICs directly
connected to the suspect components ?

thanks for your time,
rob




If you look up the "Data sheets" of those ICs - you can see what their
actions are "supposed" to be - and see if anything is failing to do it's
particular job. You can analyze the outside parts all you want - if a Chip
is failing - you won't know it without the data sheet and way to check it
for input/output. If you have an "input" signal to one of the chips - but
no output - then it isn't working. Not being able to understand the action
of those chips on that board - can leave you scratching your head a
while - and maybe running in circles looking. Checking all the traces,
switches, whatever - isn't a bad thing - but it won't uncover a dead IC -
especially if you have tunnel vision - not wanting to accept it "may" be a
chip. I'm not suggesting it "is" a chip - but the suggestion offered
couldn't hurt. You will have a much better understanding of the "intended"
performance of the circuit. Chips "can" go bad.

Here's a good one that has stood me in good stead for years. The more pins a
chip has, the less likely it is to be faulty ... !!

Arfa

[Radiosrfun]

"Arfa Daily" wrote in message
...

"Radiosrfun" wrote in message
...
"robb" wrote in message
...

"Don Bowey" wrote in message
...
On 9/9/07 5:00 PM, in article ,
"robb"
wrote:

"Don Bowey" wrote in message
...
On 9/9/07 12:09 PM, in article ,
"robb"
wrote:

The only thing that will make a difference is you posting a
schematic.

well if i had a schematic i would surely post it instead of circuit
board
pictures.

i was hoping some one might notice the chips used and there
configuration
and maybe have an idea about how and what to look for.

thanks for help ,
rob


you could make a list of the Ics on the board and download all the
datasheets for them. That should help you.

Hey Don,
I realize i am not even an electronic hobbyist more like a "dangerous
adventurere" at best when it comes to repairing electronics (i have
succesfully stripped 10 guage wire and i can distinguish resistor from
diodes most of the time)

but, how would looking up all the IC datasheets help ?

would it not be more efficient to concentrate only on the ICs directly
connected to the suspect components ?

thanks for your time,
rob




If you look up the "Data sheets" of those ICs - you can see what their
actions are "supposed" to be - and see if anything is failing to do it's
particular job. You can analyze the outside parts all you want - if a
Chip is failing - you won't know it without the data sheet and way to
check it for input/output. If you have an "input" signal to one of the
chips - but no output - then it isn't working. Not being able to
understand the action of those chips on that board - can leave you
scratching your head a while - and maybe running in circles looking.
Checking all the traces, switches, whatever - isn't a bad thing - but it
won't uncover a dead IC - especially if you have tunnel vision - not
wanting to accept it "may" be a chip. I'm not suggesting it "is" a chip -
but the suggestion offered couldn't hurt. You will have a much better
understanding of the "intended" performance of the circuit. Chips "can"
go bad.

Here's a good one that has stood me in good stead for years. The more pins
a chip has, the less likely it is to be faulty ... !!

Arfa


Don't think I ever heard that one!

[robb]

"DaveM" wrote in message
...

"robb" wrote in message
...
hello,

i posted some circuit board pics on the

"alt.binaries.schematics.electronic"

under topic ---- "pfaff UIC circuit board" to

if that will help formulate some ideas on how to repair.

thanks for any help,
rob

"robb" wrote in message
...
hello,



The way I would attack this problem would be:
Use your ohmmeter to trace the common connections from the switches to the
ribbon cable, then make sure that you have continuity through the ribbon
cable.
From there, trace the circuit to whatever component(s) they connect to.
As another poster mentioned, they might be strobed using a CAS/RAS
technique.
If either signal is missing, then the circuit won't respond to set of
switches.
It's pretty much useless to attempt to troubleshoot your problem using the
pictures you posted. You really need to get into the circuit with your
ohmmeter
and trace the circuitry. Draw a rudimentary diagram of your tracing. See
You can also power up the boards and look at the switches with a scope.
You
will probably see pulses on one side of the switches. Press one of them
and
trace the resulting signal back through the circuit and see where it goes
away.
You'll have to find data sheets on the ICs involved, so plan on doing some
Googling. Search for the part number of the part, and datasheet. Like
this:
7401 datasheet

That should get you in the ballpark.

Cheers!!!
--
Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters
in the
address)

"In theory, there isn't any difference between theory and practice. In
practice, there is." - Yogi Berra



Thanks Dave,

I appreciate your helpful answer.

I have a tough enough time with single layer trace board this is 2 layers
zig zagging through the board all over ( i know a joke to most with 6 -8
layers now common place) and well i just nowstumbled onto holding the board
up to a strong light to see both traces at same time.

I now know some of the switches feed into a DM7496N a "5 bit Parallel in
Parallel out shift register" but that does not really help me as i am not
sure of functional purpose of switches feeding a shift register other than
to count pulses maybe ?

and button lines also feed into the SN75518N a "VFD driver chip" which
does not make alot of sense to me either ?

originally i was just hoping it was a simple obvious failed component the
tracing stuff is more of a struggle
anyways thanks for the help i plan to struggle through it a bit more

thanks,
rob

[robb]

"Spehro Pefhany" wrote in message
...
On Sun, 9 Sep 2007 10:01:00 -0400, the renowned "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


What else is on the display board (part numbers)? Ca. 1987, it's
probably not a dedicated micro, but there's something else active
there to keep the number of wires down. I'm guessing it's probably a
mechanical issue on the display/key PCB (broken trace, broken wire in
the flat cable). I'd pay particular attention to the flat cable wires
(test them) and the traces going to the switches.

PCB technology isn't/wasn't always 100% reliable, especially back
then, and it's also possible that a via has cracked and is
electrically open.

Thanks for help,

that is what i was hoping for as well but it is not easy for this amateur to
find.

i noticed alot of the larger traces have bukkled up or wrinkled if that
makes sense. i am now wondering if those may lead to the problem ?

i guess i will just plod through it all

thanks again for your advice and ideas,
rob

[robb]

"James Sweet" wrote in message
news:2B1Fi.3192$qV3.2218@trndny02...

"robb" wrote in message
...
wow thanks legg,

i guess alot of detective information is allready there in the fault
description that i ignored.

namely a group of buttons have all failed yet other groups of buttons
with
different functions has not failed on the same board should lead one to
suspect a possible common shared connection between these three failed
buttons.

so look to the common connection point for all three failed buttons.

how simple and forthright yet elusive to amateurs like me.

one interesting thing i noticed is one of the alphanumeric LED cells
has
artifacts (slight glowing) displayed in it and the artifacts shimmer and
change slightly when a BAD buton is pushed could this indicate a failure
of
some component ?


Sounds like there might be a missing ground, which would cause current to
flow down paths it shouldn't. It's common for problems like this to be
caused by cold solder joints or hairline fractures in circuit boards, I'd
start by touching up any suspect joints.



thanks for helping,
that seems to be the general consensus i am just not so good at tracking
that problem i guess.

but i have not given up yet.
thanks again for help,
rob

[robb]

"Lostgallifreyan" wrote in message
...
Might as well throw my bit in too.

Forget diagnostics, just treat the most likely symptom; it's a harmless
excercise, and if it fails you can start doing tests.

Start by assuming that pressure on switches has caused a stress fracture
in
one of the address lines, so find the track common to the failed switch
group, then remove solder from the first switch terminal that track
arrives
at, and use a scriber to scratch the solder resist back along the track
about 3 to 5 mm, then reapply solder.

If that doesn't fix it, start testing stuff, starting with a resistance
(not continuiuty) test of that address line's track back to source.


thanks Lost,

i like to try simple solutions first myself. lots of good ideas and here
from everyone.

thanks again for your time,
rob

[robb]

"robb" wrote in message
...

hello,

i have posted more pics "alt.binaries,schematics.electronic" of my progress.
the front cover was held on by the 16 cell VFD so had to desolder to get
front black panel off to see the traces and other components ICs etc

thanks for looking,
rob

[Lostgallifreyan]

"Arfa Daily" wrote in
:


"Lostgallifreyan" wrote in message
...
Might as well throw my bit in too.

Forget diagnostics, just treat the most likely symptom; it's a harmless
excercise, and if it fails you can start doing tests.

Are you a medical doctor by any chance ... ? ;~)

Arfa



Nope, I am the greatest impostor, but I try to be convincing.

[Lostgallifreyan]

"robb" wrote in
:

i noticed alot of the larger traces have bukkled up or wrinkled if that
makes sense. i am now wondering if those may lead to the problem ?


Poke gently but firmly with a pin, you'll soon know if they left the deck.
That appearance is probably original though, building up the surface is one
way to get larger currents through tracks. If the resist layer (green,
usually) is entirely intact it's probably fine.

[Don Bowey]

On 9/10/07 6:13 AM, in article , "robb"
wrote:


"Don Bowey" wrote in message
...
On 9/9/07 5:00 PM, in article , "robb"
wrote:

"Don Bowey" wrote in message
...
On 9/9/07 12:09 PM, in article ,
"robb"
wrote:

The only thing that will make a difference is you posting a schematic.

well if i had a schematic i would surely post it instead of circuit
board
pictures.

i was hoping some one might notice the chips used and there
configuration
and maybe have an idea about how and what to look for.

thanks for help ,
rob


you could make a list of the Ics on the board and download all the
datasheets for them. That should help you.

Hey Don,
I realize i am not even an electronic hobbyist more like a "dangerous
adventurere" at best when it comes to repairing electronics (i have
succesfully stripped 10 guage wire and i can distinguish resistor from
diodes most of the time)

but, how would looking up all the IC datasheets help ?

would it not be more efficient to concentrate only on the ICs directly
connected to the suspect components ?

If knowing a lead goes to an IC, without knowing what the IC is and does,
tells you what you need to know, then you do not need the datasheets.
Personally, I'd be looking at and around the keyboard multiplexer.



thanks for your time,
rob