Re: Troubleshooting embedded controllers boards

On Friday, in article
<1172827109.1818.0@xxxxxxxxxxxxxxxxxxxxxx>
news@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx "Tom Lucas"
wrote:

"Paul Burke" <paul@xxxxxxxxxx> wrote in message
news:54q5urF2227duU1@xxxxxxxxxxxxxxxxxxxxx
uriah wrote:

coin-operated equipment of all types..., Redemption,..machines,
etc.etc.

I like the idea. $1 in the slot, and it saves all that bible bashing,
hymn singing, and shalt not coveting thy neighbour's ass.

:-)

How do I know if a particular chip is
working or not? Can someone please guide me on what to do? Is there
a book that shows how to troubleshoot these boards down to the
component level. I am getting the feeling that it can't be done.

That's roughly the way it is. Without a circuit diagram, you're
basically stuffed, and even with one you probably are. Simple
circuitry, standard chips, someone might be able to do it if they
charge their time cheaply enough. But most stuff is only worth hacking
if the payoff is high, like the Romanian mafia with ATM machines.


I would agree with Paul here - the cost of getting someone good enough
to hack the boards is probably more than the cost of replacing them. You
might be able to enthuse a student nearing the end of their degree to
get involved at a reasonable cost and they might have the skills to do
it but, in reality, fault-finding is all to do with experience.

However, there are some things you can do to which don't require
knowledge of the circuit but it depends on what the fault is. You can
look at all the solder joints and check their quality or you can see if
there are obvious breaks in any PCB tracks. You can check electrolytic
caps for leakage and look for any foreign bodies causing shorts on
device pins. If the PCB doesn't have tracks internal to it then you can
check them all for continuity and check connectivity to power planes and
shorts between them and other tracks (some of which might be
intentional).

As others have said the above points plus

1/ Compare against working board.
2/ Look for connectors wrong
3/ Look for BURN marks
seriously with solenoid and other motor drives in some machines
broken directly or indirectly (foreign material) can cause
these sorts of faults.

If the circuit is a proven design which passed its initial tests and
entered service then your fault is likely to be either a faulty device
or one of the things I've mentioned above. Whilst this won't fix all
your boards you might be able to fix some of them and the checks above
don't require a hugely skilled person.

Without building up your own knowledge database from knowing

A What the reported faults and fixes you find were

B What the circuit diagram of standard parts is

C Having the ability to rework newer boards with fine pitch surface
mount components.

All you are likely to be able to do is change the periphery or power
supply components at best.

That is if all the components can be easily got in small quantities, no point
repairing a few boards with one component if you can only buy them in minimum
quantities of 5000!

To achieve this may well be a lot more expensive than the value of the board.

If the boards are worth more than 5 x the managers effective hourly rate
then it might just be worthwhile spending the time building up the knowledge.

--
Paul Carpenter | paul@xxxxxxxxxxxxxxxxxxxxxxxxxxx
<http://www.pcserviceselectronics.co.uk/> PC Services
<http://www.gnuh8.org.uk/> GNU H8 & mailing list info
<http://www.badweb.org.uk/> For those web sites you hate

.

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