I have had the good fortune of working with several different automatic watch cleaning machines over the years. The Elma RM90 is the first I was ever exposed to. While it lacks the ultrasonic capabilities and digital settings of machines such as the Greiner ACS 900 and Rolex’s CM3, I find its rudimentary construction to be one of its best assets. I also find that the square-bottomed jars it uses to hold the cleaning and rinsing solutions help to compensate somewhat for its lack of an ultrasonic tank, as the square form naturally churns the solution more effectively than the round jars of the aforementioned machines. In all cases, though, whether equipped with an ultrasonic chamber or not, pegging out the jewels after the preliminary cleaning of a watch mechanism is still necessary to maintain the long-term precision timekeeping of any watch.
Recently, the RM90 that we employ in our shop began malfunctioning on us. The cleaning basket would move through the cleaning and rinsing cycles, and it would spin dry, but it would rotate to a standstill shortly after entering any of the solutions.
A similar problem had manifested itself in another RM90 I had used several years ago. The machine was sent out for repairs and we did not receive it back again for more than a month. While we could live without ours for that amount of time, it would put a serious dent in production, and neither my associate nor I were keen to let it go for that long. Especially after contacting the nearest official Elma service centre and being quoted $1900 for the repair, not including shipping. So we decided to have a go at repairing it ourselves. Our unit was three years out of warranty, so there was nothing to void by opening it, and, if our efforts didn’t yield a solution, we would spend the $2000 for an official fix.
One trip to the local hardware store and 3 hours later, our cleaning machine was back up and running like new again.
Finding the Problem
We started by opening the machine up and letting it run through the clean, rinse, and dry cycles to observe all of the internal components in action. The first thing we checked was that there was adequate lubricant in the bushing that the machine’s sliding bracket operates in and that the lubrication on the centre column was still in good condition. These two checks are the only maintenance points described in the RM90’s user manual. The centre shaft and bracket were both well lubricated, so our problem wasn’t there. Moving on, we noted that the cabling, which runs from the unit’s main circuit board to the motor, was quite taught when the motor was positioned at its lowest active point. Upon even closer observation we noticed an occasional, small spark (located in the area circled in red below) where the cables enter the motor when the motor moved between the submersed and spin-dry positions. We had found our problem area.
After removing the motor from the cleaning machine and peeling back the wire-insulation near the area we had seen the sparks, this is what we saw:
Making the Fix
The wiring that connects the motor to the circuit board is surprisingly stiff and, after years of repeatedly moving up and down inside of the machine, it had snapped inside of its sheathing. To remedy the problem, we purchased 12″ of more flexible wire from the electronics section of a nearby hardware store for 19¢ and replaced the old wiring, with slightly longer lengths, where the wire enters the motor. The fix worked great. It’s been more than six months now since we made the repair and our Elma hasn’t shown a hint of malfunction since.
Having seen a similar problem with the aforementioned Elma RM90 in the past and after having spoken about the problem with the repair centre nearest us, this quirk with the RM90 seems to be a common point of failure. As other watchmakers could probably benefit from knowing how to fix their machines when this happens to them, I thought it would be a good idea to recap the process that we went through to fix ours.
First up, the tools. Following is a list of the items we used to fix our automatic watch cleaning machine.
- 3mm Metric Hex Key
- Flathead Scewdriver
- Torx T20 Screwdriver
- Flexible 16-gauge Wire
- Wire Cutter/Stripper
- Utility Knife
- Soldering Iron
- Heat Shrink (electrical tape will also suffice)
- Unplug the machine
- Remove the flathead screws that hold the top of the machine in place
- Set the screws and their rubber washers aside, in a safe spot where they won’t get lost
- Lift the top of the machine up slightly and locate the ground wire attached to its underside
- Dislodge the ground wire from under the top using pliers
- Remove the top
- Remove the six flathead screws that hold the righthand, side panel of the machine in place
- Locate and dislodge the ground wire from the righthand panel
- Remove the righthand panel
- Detach the wires that run from the motor to the circuit board from the circuit board, taking note of where each wire came from so that you reinstall them in the correct place
- Open the glass hatch at the front of the machine and loosen the flathead screw that holds the plastic chassis for the cleaning baskets in place
- Remove the plastic chassis from the machine
- Use the hex key to unbolt the motor housing from its mount in the cleaning machine
- Set the hex screws safely aside
- Carefully slide the motor and its shaft up and out of the cleaning machine
- Use a torx T20 size screwdriver to remove the torx bolts that hold the motor housing together
- Set the torx screws safely aside and carefully remove the upper half of the motor housing
- Slice away the black, heatshrink sheathing that covers the wires leading to the motor
- Strip away the wire insulation near the area where you observed sparks, until you find where the wire has fractured (our wiring had begun to sever about an inch and a half from where the wires enter the motor housing)
- Take a length of new wire and cut away a suitable amount from either side of the original, fractured piece of wire, which will be replaced by the new wire
- Cut away 10mm or so of the wire insulation from either end of the new piece of wire as well as from the two wire ends from the machine that you will be installing the new piece of wire in
- Fray the wire that is exiting the motor housing as well as one of the ends of the new piece of wire
- Join the two frayed ends and twist them together
- Solder the joined wires together and then insulate the joint with heat shrink or electrical tape
- Reinstall the upper half of the motor housing and screw the housing back together with the torx screws from step 16
- If you will be replacing the heat shrink that originally covered the wires, now is a good time to slide it over the wires, if you will be using electrical tape or another form of insulation, skip this step
- Repeat steps 21 through 24 to attach the other end of the new piece of wire to the wire that attaches to the circuit board
- Position the heat shrink and apply heat to fix it in place or use electrical tape to bind the three wires together in order to keep them from catching on other components inside the machine when the motor moves up and down
- Reseat the motor back inside of the RM90 and fix it in position using the hex screws from step 13
- Reinstall the plastic chassis for the cleaning basket and fix it in place with the flathead screw that secures it to the motor shaft
- Reattach the ground wire to the side panel and install the panel back in place with the flathead screws from step 7
- Reattach the ground wire to the top cover and fix the cover back in place with the flathead screws from step 2
- Plug the machine in and test to ensure that everything is back in working order
Back in full operation, here is our RM90, reinstated to its rightful place in our lab:
If your Elma RM90 is beginning to exhibit signs of malfunction with the motor unit, the problem may very well lie in the wiring that connects it to the main circuit board. If your machine is still under the manufacturer’s warranty, I recommend getting in touch with Elma as soon as possible by sending them an email at firstname.lastname@example.org. Their staff are very friendly and supportive, and will go out of their way to help you in any way they can. In the event that your machine is no longer covered by the manufacturer’s warranty, I hope that the above guide will help you get your machine back in full working order again. If you are not confident in carrying out this type of repair, have it done by someone local who is trained in and has a background in electronics repair.
This post was featured as an article in the October 2010 issue of the Horological Times.