help diagnose old circuit board, fault

[Don Bowey]

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

No we don't. We generalize.

 

[Meat Plow]

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

I would tend to agree with you here.

 

[John Hudak]

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 ?

Depending on the config, shift registers were often used as switch
debouncers.
Sorry I can't help with any more diagnosis.
J

 

[Ron(UK)]

No we don't. We generalize.

All of you?

 

[Arfa Daily]

All of you?

Only when they are wearing sox with a red color ... ;~)

But actually, both are correct, depending on which side of the pond you live
....

Arfa

 

[Michael A. Terrell]

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.

Its time to help out the poor brits, again. We need to supply them
with new Electroshock Therapy Machines.

Their current design just isn't up to the job at hand. It has
settings for Fop, Layabout, and Damn Demented Donkey.

What they need is the new model with 'Straighten out your shit, or
else', "You've been warned', "This is you last chance!', and 'Cinder'
settings.


--
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

 

[Ron(UK)]

What they need is the new model with 'Straighten out your shit, or
else', "You've been warned', "This is you last chance!', and 'Cinder'
settings.

Ahh, the American way.. god bless America

 

[John Robertson]

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 :-#)#
--
(Please post followups or tech enquires to the newsgroup) John's
Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com "Old pinballers never die, they
just flip out."

 

[Gary Tait]

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

They use the same I/O lines to multiplex the display and the keypad. Not at
all uncommon.

 

[robb]

They use the same I/O lines to multiplex the display and the keypad. Not at
all uncommon.

Thanks Gary,

Could you elaborate on that a bit more ? as i am a mere amateur

i have traced one side of switches back to the Q22-Q30 lines ?

the general layout is ...
that two button/switches {increment, decrement} will share a line to one
Q## output and repeat for 12 pairs of buttons (total 12x2 or 24
button/switches)

the other side of the switches get bundled/connected together into two
groups of 12, that each group shares one line down the ribbon to the main
controler board (with 12k resistor just before going down ribbon wire)

so the Q## pins on the SN75518 are Outputs ... So i guess there is some sort
of timed pulsing and controler board has to figure out which button was
pressed ?

thanks for your help,
rob

 

[robb]

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 sewing
machine

a for fun project for me , a challenge

ok i have posted partial schemat that i made by hand for the pertinent part
of the button circuit board it does not include the VFD connections which
are inline with the button connections nor the indiocator LEDS that mostly
just connect to the DM7496 chips.

id therea good way to turn a MM into logic probe ? i am using the Fluke 177
true RMS meter


thanks again for any help,
rob

 

[robb]

that was posted on the

alt.binaries.schematics.electronic

rob

 

[robb]

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 sewing
machine

a for fun project for me , a challenge

first thanks to everyone for your time and help,

OK, so i followed most of suggestions from everyone

check and follow traces from the switches, to ribbon, to the VFD SN75518
and to the main board ( traces ok ) then probe signals from the buttons
(problem)
so i connected up my toy O-Scope (you'd never guess and fall on floor) and
found no signal from the two VFD pins going to two broken butons and a
mangled signal to the other button that does not work

i noticed several pins not connected to anything with good wave form can i
just reroute the broken lines to those or do i need to just replace ic ?

thanks again for help from all that tried,
rob

 

[Michael A. Terrell]

Ahh, the American way.. god bless America

Have any stray British EE donkeys that you'd like to test it on?


--
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