Repairing a BT Baby Monitor 250 Power Button

My BT Baby Monitor 250 has a faulty power button as a result of toddler ‘droppage’.

The power button requires hard pressing and no longer has the ‘click’ it used to. It also doesn’t always reliably turn on at all.

Time for a repair!

Dismantling it!

Step 1

Remove the battery compartment cover, as well as the batteries.
Along the bottom edge of the compartment are a pair of phillips screws – remove these.

Step 2

The two part case is now held together by a pair of snap-together clips on each side. These can be opened with some judicious levering. The catches are shown here, circled in red: (case removed for clarity). Levering the case outwards at these points will help to release them. The case halves can then be separated.

From the side:

Step 3

Gently lever out the pair of plastic clips holding the LCD to the printed circuit board.
It then lifts off, and hinges downwards.

One clip is visible here:

Step 4

Remove the two small phillips screws under the LCD holding the PCB down

Then, remove the screw at the bottom of the PCB.

Step 5

Gently fold the metal contact terminals that stick out through the bottom of the case inwards, and carefully prise the circuit board free from the case. (These are visible in the picture above)
You might want to remove the vibrate motor from the bottom half of the case (it’s just press fit) to get more wiggle room.

Find the problem

On inspecting the surface-mount power switch, it was apparent that its’ two securing lugs at the front had come loose from the PCB. They were originally soldered, but the solder has fractured, leaving both the pads and the tabs intact.

I simply resoldered these to the board, and quickly resoldered the joints on the two contacts at the rear of the switch to make sure they had good contact to the pads.

Reassemble

Reverse the above steps to reseat the PCB into the case, resecuring it with the three screws, (vibrate motor as well if you removed it), then refit LCD back into place.

Check at this point that all the buttons have a normal ‘click’release’ feel to them, (if not, sometimes the little plastic sticky foam pieces on the end of the plastic ‘button pressers’ have come adrift…)

Then snap the case back together, seating the top part first. Replace two screws under battery compartment. Refit batteries and test.

Done!

Delonghi Perfecta machine fault – no steam!

I was given a machine from a work colleague to fix (a snazzy Delonghi Perfecta bean to cup machine) which wouldn’t froth milk or generate steam but did make coffee.  When asked to steam, it just displayed “Heating Up…” then returned to the main screen.

I guessed the steam boiler element had probably failed open circuit, so opened the machine up, and checked its’ resistance with a multimeter (which was around ~50 Ohms), so that wasn’t the problem.

The boiler element is protected by a pair of thermal cutouts, which will permanently blow (open circuit) if the element overheats to prevent a fire.  Both of these had failed.  So I thought that buying a new pair of these would solve the problem.

Then I found this article detailing a similar fault, where the triac which controls whether the element is on or not fails closed circuit, meaning the element overheats and blows the thermal fuses.  That article discussed the triac powering the main boiler rather than the steam boiler, but both are driven the same way.

This seemed to make sense and would explain why the thermal fuses had been blown.

Testing (carefully!) with the multimeter, I found that the element was continuously powered with full AC voltage even when the machine was on standby, so it became clear that the triac had failed closed circuit in this case.

So, to fix the machine, I replaced the two thermal cutouts from 4Delonghi: 2933924OH

and the triac (from RS): Part No BTA24-600BW. From RS, it’s 6871029

 

and everything worked happily!

Here are a few photos of the repair:

The horseshoe-shaped steam boiler (behind the back cover of the machine). You can see one dangling thermal fuse which I’d unbolted, the other at the centre of the image, and the two terminals of the boiler element. Both fuses are wired in series with the element – one in series with the triac-switched feed from the control board – lilac wire, and the other in series with the neutral return (brown wires).

 

 

 

The control board, with the failed triac indicated with an arrow.  The one on the other side of the heatsink controls the boiler for the hot water. (and can fail in a similar way!)

 

Faulty triac closeup (arrowed)

 

The resoldered and re heatsink-compounded triac on the main circuit board prior to reinstalling the retaining clip and reassembling the machine.