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Tinkering: 2020-06-06: Braun BNC008-RC Alarm Clock Dismantling and Repair
The Braun BNC008-RC is a very small radio-controlled digital alarm clock, only 58mm square and 20mm thick. It has radio control for several countries, i.e., it can receive radio signals from clocks on several different frequencies. I am used to alarm clocks that receive the German DCF77, but this one can do a lot more: UK, US, Japan. Because I found it quite interesting that Braun fit everything is such a small enclosure, especially the antenna, I bought one of these small alarm clocks. On eBay.
The clock looks nice. There are some things that could be improved ergonomically, but I don't want to talk about that. Because unfortunately, the clock I got was broken. It would not beep. The alarm clock worked except for the alarm. So I wanted to send it back and get a replacement. Unfortunately, the eBay dealer did not respond to my request. After a few days, I opened a case with eBay, and eBay booked back my money the next day, because the dealer had still not responded.
So I got a nice looking alarm clock for free, but the alarm is broken.
Clearly, it's time to take the clock apart. Of course, I'll try to repair it.
The first challenge was opening the clock. There was no visible screw. The enclosure is a single piece of plastic. After scratching my head for a while, I concluded that the only possibility would be that the front is glued on. So I worked my way in with a knife and pried the front open. Indeed, that's the way in. Underneath the front, there is a frame with four screws. By removing those, the clock can be opened.
The front is glued on with strong double sided tape. I found it virtually impossible to avoid scratches when removing the front. Be careful. Maybe don't use a sharp metal knife like I did. My scratches mainly removed black paint, so I used a black pen to hide the evidence of violence. It worked quite well.
The frame that holds the clock together has a notch on one side (at the bottom of the picture). Remember this, it's where the alarm button goes.
The display folds open to the left.
The antenna is on the bottom. Interesting detail: the ferrit core is flattened to fit into the restricted space.
On the back of the display board, which is the main PCB, there are several small crystals for tuning in the different radio frequencies. They are hidden behind some black plastic foil in the corner of the PCB (not visible at the left edge in the picture).
The buzzer is a bare metal piezo buzzer. One cable is loose! Yes, it's hard to see, because all that stuff is on top of the problem.
The solder broke off of the piezo ceramic. That shiny metal droplet is not connected. It is not a super thick wire, but in my opinion, the wire is still too thick for the weak solder connection with the ceramic, and the bending forces of the wire were probably strong enough to make the connection fail.
Of cause, the problem is hidden under several layers of stuff. First, I need to remove a small PCB with an inductor which is glued in. The knife helps to cut the glue. To get out the board with the alarm buttons, a plastic spacer that pushes it up and keeps it in place needs to be removed. After that, the buzzer is accessible. That white wire in the middle of the picture is loose (it looks in the picture like it connects to the display PCB, but it does not).
I cut off the solder, because I use leaded solder and I am sure the original is lead-free. Mixing the types is not a good idea, so I started with a fresh copper wire. Soldering the wire to the buzzer is really not easy, and the connection feels like a weak adhesion rather than a good metal soldering connection. Let's hope it won't fall off again.
After the repair, everything can be put back together. Be sure to clean the display of finger prints and dust.
Reattach the frame. Remember to put the notch up to avoid interfering with the alarm buttons.
Be sure to clean the display.
Attach new double sided tape. I removed the old tape and all the glue with some limonene, but it also works with patience. In fact, even with limonene, patience is necessary.
Be sure to clean the display.
Clean the front. Then carefully place it on the clock.
Done. See that white spot in front of the '2:01'? That is me not having paid enough attention to removing dust.
The finger prints are on the outside and can be cleaned off now.
Finally, the nice alarm clock can fulfil its purpose!