Mouse Hunt - Day 2

Last semester, while I was away on sabbatical leave, the large telescope at CFO became inoperative. Closer examination showed that a mouse had invaded the telescope cable conduit, built a nest, and chewed on the cables. This is undoubtedly the primary cause of the malfunction, however there may be secondary effects due to shorts produced by the exposed wiring. On these pages, I will document the discovery, cleanup, and repair of the wiring.

Day 2: Feb. 15, 2005 - Checking the Control Electronics.

The goal today is to get into the control electronics and check for further damage. I will also clean and sanitize the cables and check them for chewing damage.

1. Start by removing the back panel of the control box:

2. The cables look pretty clean. There are some droppings on the bottom of the box.


Each of the cables was removed, cleaned, and disinfected up to the wall feed-through where the mouse nest was. A visual inspection for mouse damage showed that there was no apparent damage beyond the two chewed cables discovered yesterday.

3. The top drawer of the control box contains the drive electronics. Clearly the mouse has been in here too.

4. I'll have to take out the main drive board to clean it and underneath.

5. He apparently didn't spend too much time around the motor power supply and fan: there's some sign here, but not much.

6. More droppings near the cabling.


After I finished cleaning up the drive electronics, it was time to open the bottom drawer and check out the computer.

7. This doesn't look good. Clearly the mouse spent more time here than in the top drawer.

8. How did he manage to get stuff under the computer?

9. Uh oh. This looks bad. These mini-coax cables have been chewed through. I'd better check inside the computer.

10. Yup. Chewed through.

11. Here's the smoking gun. These two mini-coax cables carry signals from the computer to the drive electronics in the upper drawer that was just cleaned. These signals control how fast the telescope's Right Ascension and Declination motors turn. By chewing through these two little wires, the mouse completely disabled the main telescope.

Conclusions:

The mouse entered the observatory in the crawl space under the (unheated) main dome. Once there, it followed the control cables and climbed them, passing through the wall feedthrough into the conduit in the warm room, where it built its nest. It then followed the cables down the conduit, across the wall, and down into the control computer, with occasional rest stops and snacking on wire insulation. It got into the computer itself through a hole in the back through which the control wires emerge. In the computer, it chewed completely through the two wires that controlled the primary motors of the telescope.

Now that the damage has been assessed, and the mess cleaned up, it's time for repair.

Repair Plan:

1. First, replace the two chewed-through mini-coax wires.
2. The longer control cables are too difficult to replace, so they will have to be repaired. There are two options:
   1. If the individual wires in the cable are still intact, it might be good enough just to remove the ruined cladding, cover each exposed wire with electrical tape to prevent shorts, and overwrap the whole thing to get some mechanical stability back.
   2. If the wires themselves are damaged, we will have to cut out the damaged section and splice the remaining cable back together. This will shorten the cables somewhat, but that is not a problem since the cables are much longer than needed to reach the telescope.
3. Put everything back together and hope the telescope starts working again. If it doesn't, then the mouse-induced shorting has caused some electrical damage as well. Let's not borrow trouble - I'll deal with that problem if and when it becomes real.
4. Finally, I hope, at least block off the wall feed-throughs so that another mouse can't get into the warm room this way. We should also see what can be done to mouse-proof the crawlspace under the main dome where the original entry happened.

You can follow the first stage of the repairs here

Page maintained by D. Briotta (briotta@ithaca.edu) Physics Department (home page) Ithaca College (home page)