Re: Lost steps

>
>> All of this is redundently grounded to the chassis/case. The power
>> cord is grounde, the rectifiers are grounded, the 37 Volts is
>> grounded, the 5Volts is grounded, and each board is grounded on all 4
>> corners to the ground trace which also grounds both power supplies.
>
>Hmm, someimes there can be TOO MANY grounds, causing all sorts of
>circulating currents, known as ground loops. You might take a voltmeter
>and try reading both AC and DC between the computer case and the driver
>cases. If there is much voltage difference, it could easily explain the
>problem.
>

Another thing to check is your foil shielding. If it is grounded on both
ends, these ground loops can result in a voltage drop across the shield,
which can induce noise currents in the shielded conductors. The shield
should be grounded only at one end, preferable the supply end.

Also, when you say "foil shield", is this ordinary aluminum foil? It
can be difficult to get a good connection to aluminum foil. You might
try wrapping an uninsulated "drain" wire around the outside of your
foil (sort of like a twist, not like a noose). Again, ground this only
at one end.

HTH.

++
Terry