help diagnose old circuit board, fault

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.

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

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.

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

"robb"

board

configuration

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.

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

Arfa

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!

cable.

technique.

switches.

ohmmeter

You

and

away.

this:

in the

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

and

sewing

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

with

has

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

in

arrives

thanks Lost,

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

thanks again for your time, rob

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

"Arfa Daily" wrote in news:qCbFi.7176$ snipped-for-privacy@newsfe2-gui.ntli.net:

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

"robb" wrote in news: snipped-for-privacy@corp.supernews.com:

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.

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.

I would tend to agree with you here.

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

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.