Open Sesame !
Posted on November 11, 2024 in Hardware
Recently, the CD player on my HI-FI system refused to open. Pressing the “Eject” button had no effect. Of course, I tried disconnecting and reconnecting the HI-FI system from the main supply, without success. The only thing left to do was to dismantle it to find out what was causing the problem.
My HI-FI system is a Denon RCD-M39. The information I give here is, in part, specific to this model. The troubleshooting principle, is "universal". It applies to any device.
As an electronics engineer, my first instinct was to think that the problem is a broken solder joint or a faulty electronic component. So I searched the RCD-M39's service manual to find out which part of the electronics might be faulty. Surprise, it's very easy to find. What's more, it's very complete. All the diagrams are provided as other interesting information.
But if you think about it twice, what is the component most likely to fail in the CD drive's drawer opening/closing system ?
The motor.
On several occasions, I've seen a DC motor (with brushes) break down. A mechanical failure, the brushes no longer touching the rotor commutator for one reason or another.
The aim is to find the motor and determine whether or not it has failed.
To dismantle the CD door open/close motor on the RCD-M39, you need to remove the front panel. Obviously, the first thing to do is disconnect the mains plug. But be careful! Even when unplugged, the power supply electronics, located at the rear of the RCD-M39, remains dangerous. The large capacitors can store energy for several minutes, even, hours.
Disassembly of the front panel begins with removal of the HI-Fi system's central cover.
To be able to work in good conditions, once the front panel has been unscrewed, you need to remove the cables from the connectors located just behind the front panel.
Location of conectors to remove.
Before the motor can be removed, the CD cover must be opened manually. To do this, insert a screwdriver into the dedicated slot under the HI-Fi system and push as indicated by the arrow below.
Manually open CD drawer.
By adjusting the drawer opening manually, you can gain access to the motor retaining screws.
Motor screws.
Remove the screws, taking care not to lose the belt.
On the other side, remove the motor board by removing the screw and connector on the right.
Motor connection board.
We then have a motor + board assembly. For easier handling, it's best to unsolder the motor from the board.
The motor and it's board.
The motor is a popular model, the RF-300C-11440.
Le motor.
To check that the motor is working, simply apply a voltage of 2 to 5V to its terminals to see if it starts. Caution: to be sure of its operation several starts/stops are needed. The reason is that the motor may or may not stop in a position that allows restarting. By lightly braking the engine with your fingers, you can better detect any problems. An engine that doesn't “run smoothly” is also a sign of a problem.
- The motor is faulty ? Two solutions.
- Replace it. This type of motor is widely used by manufacturers. It's easy to find on the Internet. Simply weld it in place of the faulty motor. Then reassemble the HI-Fi system, of course. Be sure to take the pulley from the original motor and fit it to the new one.
- Repair it. It's tricky, but it can be done.
Motor repair :
In my case, the engine doesn't start every time. You have to help it start with your fingers. I decided to try to repair it.
To repair the motor, start by opening it. To do this, you need to remove the plastic pulley from the motor shaft, then loosen the cage lugs. How do I do this? You're on your own ;)
Motor cage lugs.
Once the motor cage lugs have been loosened, remove the motor's back plate, taking care not to cut any of the wires.
We can then carefully remove the rotor.
Under the microscope, the problem becomes clear. The rotor brushes and collector are very dirty.
Dirty brushes.
The collector is also very dirty.
The collector is easy to clean. A cotton swab and a detergent (alcohol, acetone, etc.) are all you need. Just make sure that no cotton fibres have been deposited during cleaning.
On the other hand, cleaning brushes is a very delicate operation. Brushes are made of very thin metal. They are very fragile. I also used a cotton swab to clean them, but a non-fibrous material would have been better. The cotton fibers catch to the brushes very easily. Pulling to unhook them is a very bad idea. I managed to clean the brushes, but one of them got bent in the process. Fortunately, I was able to straighten it properly.
Cleaned brushes.
Cleaned collector.
Once cleaned, the motor reassembly operation is equally delicate. Don't forget to put a drop of oil on the the collector to lubricate it. This motor also has a plastic washer that fits over the bronze bearing on the stator, under the brushes. Don't forget it.
I had to make several attempts before I managed to reassemble the motor correctly. After each attempt, I had to straighten the brushes. To achieve the reassembly correctly, I pushed on the stator axle to get it as far out of the cage as possible. Then slide the collector between the brushes before pushing it back into the cage.
Last operation, tighten the cage lugs. And, of course, reassemble the HI-Fi system...
As we've seen, the motor repair is possible but difficult. Especially as the motor is small.
In my case, the operation was a success. The motor is still running after a few months :)
Translated with the help of DeepL.