Service Note #1 Author: Tom Droege Date: 001128 1) A fix to make the RA drive less prone to stalling. 2) A possible improvement to the focus motor drive. 3) Improving the Dec. Drive 4) Camera Head Clock Drive Modification 5) Clock Levels 6) Operation for best focus 1) RA Drive motor mod. This requires removing the motor drive board and performing a couple of cuts and pastes. The result is that the motor full steps with much more torque. This is only necessary if you have trouble with the RA drive motor stalling when it gets cold, etc.. Everything else stays the same. No program or speed adjustment is required. It just makes half as many full steps. I cannot see any change in tracking. The change should be reversible. You should be able to easily make this change. Here is how to do it: Find drawing M1 RA MOTOR DRIVE Remove the motor drive board from the telescope. It is labeled MAW980710 It has one big and two little MT cables going to it and a wiring harness. It also has the pot where we adjusted the RA drive frequency. In the lower right corner you will see a switch. It is labeled 4053. Find this chip. It is probably an HC4053. You will find it second up in the middle on the end of the board with two connectors. Pin 2 and 5 are to be cut from where the go to the 03 and tied low. On our board we did this on the board top. We cut the lead from pin 2 by the pin. We cut the lead from pin 5 where it comes out of the bottom of the chip (going to pin 2 of the 03). Now we tied pin 2 to 5 to 8 on the chip top. Show the above to your favorite electronic tech. If he seems at all confused about what to do, then send it to me. But it should be not problem at all to anyone used to fixing electronics. 2) Focus Motor Change. This requires some machining. The scheme is to drive the focus closer to the center of the camera. This requires removing one of the trombone slides from the camera, doing some machining on it and making a couple of extra parts. Easy job for your machine shop. When Dan comes in on Saturday he will make proper drawings. I could fax you a sketch now. This makes a significant improvement on how much the focus drive tilts as it is moved. The basic idea is to drill out the hole where the lead screw attaches. This is then extended through the hole to a bar that is then attached at the center of the camera support bar. Sounds really kludgy, but it works. Additional observation makes this conclusion less certain. It may or may not do any good. See note 6) below. 3) Possible improvement to the Dec. drive. I find that the gear on the motor was slipping a little due to the high torque. I just took it off, and glued it to the shaft using JBWeld. Now it does not wiggle. This is not an irreversible move since the whole motor assembly can still be removed and replaced. The large gear has three set screws. It too wiggles back and forth a little. Two of the set screws just push on the shaft, the third goes through the shaft to pin it. The hole through the shaft is a little too large, so it is possible for the large gear to move a little on the shaft. A dangerous (irreversible) fix would be to fill the through screw hole with JBWeld and insert the screw. This would prevent the wiggle, but would require sawing the shaft in two to ever take the assembly apart again. Not too bad an operation. The parts are not that expensive. You might first try tightening up all three set screws. (Note later serial numbers will have a tight pin through this shaft.) 4) I have added a resistor in series with the vertical clocks in the cameras. Again, no big deal for your experts to do. But I think it does nothing, and am just adding it to all the camera heads so that they are all alike. 5) Change of clock levels. The only change of significance is the change of VVH from +6 to +3.9 Clock Old New VRH 0 0 VRL 10 7 VVH 6 3.9 VVL -8 -8 VHL -5 -3 VHH +5 +6 6) The focus drive is still not satisfactory. It wants to skew, then suddenly jump to a new position. I have found that the focus drive works best with the telescope pointing straight up.