help diagnose old circuit board, fault

[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]

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]

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]

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]

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

 

[Anthony Fremont]

robb wrote:

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]

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

 

[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).

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]

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

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]

robb wrote:




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.

 

[Jamie]

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.

 

[Michael A. Terrell]

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]

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]

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]

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]

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]

On 9/9/07 12:09 PM, in article [email protected], "robb"

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]

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]

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.