Theory of Operation:
The signal to operate the shutter originates on the timing and control
board, probably from the EPROM. There is an output circuit that
sends a signal to an optical isolator in the shutter Control
Box, which in turn drives a circuit that controls the power
output drivers that there was a problem with the optical
isolator not turning on hard enough, so the signal was not
getting to the power amp. There were resistors in the circuit
that related to the values used on the red side, and they did
not allow enough current to flow through the LED of the isolator
so it's output transistor was only going down to a marginal
operating voltage for TTL logic. This was fixed in the Shutter
The shutter is operated by two 12v, magnetically latched solenoids.
Too open or close the shutter, the solenoids are pulsed with a
48v pulse approximately 50ms long. The current to one solenoid
is reversed, to oppose the magnetic field of the latching
magnet, while the other adds to the latching magnet field. This
results in a very fast transition from open to close or vice
versa. After the pulse is gone, there is no current through the
solenoids, so the magnet in the one with the armature seated
maintains (latches) the shutter open or closed, while the other
armature is extended and thus the magnet does not have enough
force to pull the shutter back.
- Allen wrench set
- Telescope mirror
- Lint free towel
Removal of Solenoids
Power off the shutter control box via software. Use command "m poweroff=28" at a punaluu xterm window.
Remove the blue electronics cover.
Verify that power to the shutter control box is off by observing the red or green LED's on the shutter control box. Both LED's should be off.
Disconnect the AC cord from the shutter control box.
Verify scribe marks to the mounting brackets on the existing bad solenoids. Make scribe mark if necessary.
Disconnect the two terminal lugs (+ and -) on the solenoid(s) that are being replaced.
Verify that terminal lugs are still labeled with the correct polarity.
When replacing the "CLOSE" solenoid, place a lint free cloth at the bottom of the bracket to prevent any screws from falling into the gimbal.
Remove (4) 8-32 x 3/8 socket head cap screws that hold the solenoid to the bracket.
Slide solenoid out.
Installation of Solenoids
- Measure resistance of new solenoid. The reading should be around 25 ohms.
- Transfer scribe or mark from the old solenoid to the new solenoid.
- Using a telescope mirror and hands free light verify that the Hall switch for the shutter actuator lines up. If replacing both solenoids, make sure that both open and close solenoid switches line up.
- Mount new solenoid on bracket using the (4) 8-32 x 3/8 socket head cap screws. Do Not Tighten.
- If installing two solenoids, follow steps 1 thru 4 on the installation procedure.
- With LRIS parked at 90 degrees (dewar at 3'oclock) remove the access panel on the left side. This will give you access to the inside of LRIS to make the visual alignment of the shutter.
- While one person is moving either the close or the open solenoid on the bracket, the other person will visually align the shutter. See note 1 below.
- Once the open or close position on the shutter is set, tighten the socket head cap screws.
- Remove the lint free cloth.
- Plug AC cord on shutter control box.
- Turn software power back on. Use command "m powon=28" at a punaluu xterm window.
- Verify that either the red or green LED's on the shutter control box are on.
- Manually cycle open/close switch on shutter control box and verify that shutter works properly. See note 1 below.
- Cycle shutter remotely. At punaluu xterm window use command "mb cshutter=0" and "mb cshutter=1." Verify that the shutter works properly. Also verify that the LED's on the shutter control box function properly.
- If all works well, secure the area.
- The shutter leafs should not be set all the way open or all the way closed. Damage can occur if set in either of these positions. In the open position, the shutter must not vignette the ccd.
- This task will require two people to complete.
- Solenoid info:
- Guardian Electric Manufacturing Co.
- P/N: A420-067897-00
- 4. Reference drawing numbers:
- 112429 - Blue Shutter Board I/O
- 112430 - Blue Shutter Board Logic and Driver
- 112435 - CCD Utility Extension Card
- 111432 - Shutter Box Wiring