Re: [Emc-users] Servo Amp Documentation?

[Gregg Eshelman via Emc-users]

 In the 1990's I fixed so many computer mouse cords. They'd get a broken wire 
where the cord exited the mouse. Often the problem was caused by the cord being 
too well restrained so it could only bend right at the exit point so often a 
bit of plastic carving was done to make sure it didn't break a wire again. An 
odd thing I noticed was only the cheaper mice ever used a molded strain relief 
on the cord. Microsoft, Mouse Systems, etc didn't.
   I even repaired the switches. The flat ones with a button on top had a metal 
snap dome inside, which would crack. Some careful work with a knife and 
superglue was done to transplant good domes from right switches on very dead 
mice to left switches on mice with just the bad switch.
But then the price of mice went way down so it was no longer worth it to fix 
them.
 On Saturday, December 5, 2020, 03:51:46 PM MST, Karl Schmidt <k...@lrak.net> 
wrote:  
 >> Unfortunately the wiring is very simple in this machine. (It's just a small 
 >> sign router.)  There is a main control 
>> board, with a couple of daughter boards (one for coms the other is the main 
>> brain) the encoder cables are plugged into 
>> the main board, as are the limits, and some other misc IO. Then there are 3 
>> ribbon cables one for each amp.  That it.  
>> I've checked the integrity of the ribbons and they all seem fine.  There 
>> isn't a bunch of individual wires anywhere 
>> that one could come loose and cause this.  The amps only have 4 other wires 
>> 2 for the motors and 2 for the DC supply.
> 
> You might check the states of the inhibit outputs, that seems to be the only
> way the drive signals a fault.

Most electrical hardware problems turn out to be connectors.  Also - on 
machines that move/flex wire - proper strain 
relief is a must - and a lot of equipment is made with the wrong type of wire - 
if it flexes too many times - like on a 
router - wires break (usually right at the connector or some strain relief) .

There are people that make $pecial wire for robotics - but if you don't need 
documentation, just use wire with lots of 
strands ( I've used 22ga with 60 strands) and strain relief to limit bend 
radius - the bits that matter.  I used 
silicone wire from bntechgo to fix a 3D printer that wiggled itself to death. 
(This is the type of wire they make test 
leads out of so fidgeting technicians don't create intermittent connections)  
Automation Direct has some shielded high 
flex wire.. (didn't have to buy a full reel).

But more important than the wire - it is where the wire meets the connector 
that fails - or where the connector meets 
the circuit board. ( I once made a small pile of money fixing some Chrysler 
instrument panels - they would develop 
cracks in the solder on the connector joints - intermittent - so very hard to 
diagnose - I had to use a microscope to 
actually see most of the cracks - remove and replace the solder and all was 
well)..

PCB to connector joints with early no-lead solder were particularly bad ...

Most of the other wire in a machine - even if it vibrates a bit, you can get 
away with MTW type stranding.  
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