Vixen DMD-3 hand controller problems

My just purchased (used) DMD-3 controller has a problem. When I first
put on the power source, the led lights up very brightly and I hear
the motors. As soon as I attempt to slew at 16X on the RA, the thing
either loses all power or the LED is lit very dimly with no power
reaching the motors. After I remove the power source for a while, it
repeats all over. Now after it stalls or goes out all together if I
pull the power source and then put the power source back on the DMD-3
is still acting like no power. Only after an extended period (after I
disconnect the power source) of time will the power come back on, and
the whole procedure repeats. Any ideas? Thanks Bob Midiri

"Bob Midiri" wrote in message
om...
My just purchased (used) DMD-3 controller has a problem. When I first
put on the power source, the led lights up very brightly and I hear
the motors. As soon as I attempt to slew at 16X on the RA, the thing
either loses all power or the LED is lit very dimly with no power
reaching the motors. After I remove the power source for a while, it
repeats all over. Now after it stalls or goes out all together if I
pull the power source and then put the power source back on the DMD-3
is still acting like no power. Only after an extended period (after I
disconnect the power source) of time will the power come back on, and
the whole procedure repeats. Any ideas? Thanks Bob Midiri

Some troubleshooting steps:

1) Exchange the plugs for the RA and Declination motors to see if the
problem is associated with the RA motor or with the hand controller itself.
If the problem is with the motor, make sure nothing is mechanically
obstructing it. Does the mount move smoothly with the manual fine controls ?
Also, does the back of the hand controller get (very) hot just before the
power cuts out (normally it's just warm)?

2) Make sure your power source can deliver enough current to run the motors
at 16x sidereal rate. I assume you're using Vixen MT-1 motors ? The power
source should be able to deliver at least 1A for prolonged periods of time.

Jeroen.

"Bob Midiri" wrote in message
om...
My just purchased (used) DMD-3 controller has a problem. When I first
put on the power source, the led lights up very brightly and I hear
the motors. As soon as I attempt to slew at 16X on the RA, the thing
either loses all power or the LED is lit very dimly with no power
reaching the motors. After I remove the power source for a while, it
repeats all over. Now after it stalls or goes out all together if I
pull the power source and then put the power source back on the DMD-3
is still acting like no power. Only after an extended period (after I
disconnect the power source) of time will the power come back on, and
the whole procedure repeats. Any ideas? Thanks Bob Midiri
Is your power source adequate to deliver the current needed during slew?. It
sounds as if it is drooping massively, and possibly shutting down with a
thermal protection circuit, when asked to drive the scope fast. The peak
current is a lot more than it may seem.

Best Wishes

"Bob Midiri" wrote in message
om...
My just purchased (used) DMD-3 controller has a problem. When I first
put on the power source, the led lights up very brightly and I hear
the motors. As soon as I attempt to slew at 16X on the RA, the thing
either loses all power or the LED is lit very dimly with no power
reaching the motors. After I remove the power source for a while, it
repeats all over. Now after it stalls or goes out all together if I
pull the power source and then put the power source back on the DMD-3
is still acting like no power. Only after an extended period (after I
disconnect the power source) of time will the power come back on, and
the whole procedure repeats. Any ideas? Thanks Bob Midiri

Have you measured the voltage of the power source? Under minimum load (RA
normal speed) and under load (16x).

If my memory serves me correctly, it needs to be a couple of volts over
5volts under load, to allow the 5volt regulator to operate properly. In fact
running it from a 12volt source seems to a little over the top. The 5volt
reg on my DMD-3 gets very hot! I remember testing my unit right down to 7
volts with no problems on the Vixen SP loaded with a C8 + bits. I
compromised at just under 9volts .... everything seems fine.

As Jeroen says, it also needs to deliver around 1 amp.

Cheers, Bob.