[DoN. Nichols[_2_]]

On 2011-12-26, Chief McGee wrote:
Looking for someone who can repair the driver boards for a Series 1 CNC
Bridgeport that has been co
nverted to AHHA controls.
Thanks, Chief Mcgee

Which of the Series-1 machines -- one in the BOSS-3 to BOSS-6
range (with stepper motors), or one of the later machines with servo
motors? They were all Series-1 machines.

If it is the stepper version, *and* if the conversion used the
original driver boards -- the most likely failure is one or more of the
power transistors on the big heat sink at the back edge of the
electronics chassis. IIRC, there are four transistors per axis, so that
is twelve total on the heat sink.

And -- the most likely cause of failure is if you are using a
rotary converter to drive the spindle motor and the electronics. Unlike
many more recent ones, this uses all three phases -- one per axis to
derive power for the steppers. The problem is that a rotary converter
tends to be unbalanced in output voltage, so one axis gets too much
voltage. As I mentioned below, the output transistors are marginal in
handling the voltages applied, so this can induce failures.

And -- under normal use with the original computer, it has three
magnetic amplifiers (also called saturable reactors) to reduce the
voltage to the drivers -- until the stepping speed is high enough to
need full voltage. (A stepper just holding position or steeping very
slowly will overheat at the higher voltage needed at the higher step
rates.) IIRC, it is 50V on the driver transistors when slow or holding,
and 80V when fast stepping. Does the AHHA controller switch the voltage
of the stepper drivers as designed?

Anyway -- at 80V, you are very close to the limits of the power
transistors around which it was designed -- but those were what was
available at the time. Today, probably IGFETS or something similar
would be a better choice -- but that would require redesigning the
amplifier.

I guess that it could be a failure of the driver boards instead,
but that is likely to also lead to failures of the output transistors.
(Otherwise, I would suggest exchanging two of the boards to see whether
that moves the symptoms to a different axis.

Best of luck,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---