Fixing a Samsung SCX-4725FN laser printer

My friend called me about a Samsung multi-function laser printer that didn't wanted to properly power on anymore. I said that I don't know anything about printers, but that it sounded like a PSU fault (as always...) and that he could try to google it. After just a few minutes he sent me this link, apparently describing more or less the exact same problem that he had. So I said, sure, if it's only a cap I can always take a look at it.

Said and done, I opened it up and here's what I found

The PSU at the back of the printer. The faulty cap in red square.

The faulty swollen cap in red square.

 It was identical to the one pictured at Flickr. The PCB was brownish around the cap indicating heat from the resistors. As this wasn't enough, the poor cap must also tolerate heat from the heatsink right next to it. No wonder it can't hold up for too long (this one about 5 years). On the other hand, it wasn't the worst cap model available that is normally rated for 85 degrees Celsius, but a slightly more tolerant, rated for 105 degrees C and 3000h.

The cap was easily replaced with a new one, this time with one that should withstand 105 degrees C for 10000h. I think something else will brake before that next time the printer fails ;)
Below is the result.

New better cap in place.

Printer up and running again.

Building a Scalextric Digital 'Autopilot'

This Christmas I wanted to build something Scalextric-related for my nephew, so I figured a custom built dual channel 'autopilot' could be a fairly simple but very useful thing. Autopilot maybe sounds a bit too high-tech compared to what this device actually is. Simply put, it's only a custom built hand controller without spring-returned throttle. Nevertheless, it can be fun to have if you don't have any friends over but still want to have some other cars on the track (so called pace cars).

Here's a quick guide how to build one yourself.

What you need

• A suitable box
• A cable with a 2.5mm plug for each channel
• Two buttons/switches per channel (brake switch can be left out if not needed)
• One 5 kohm linear potentiometer + a suitable knob
• One 17.6 kohm resistor for the brake switch per channel
• One 8 kohm resistor for the lane change switch per channel

Instructions

To start with, a schematic of a hand controller.

Schematics of a Scalextric hand controller and which is replicated in the autopilot.

When the electrical connections figured out, get a suitable box to fit the amount of channels you will be using.  For cabling I used a 2.5mm stereo plug-plug cable that I cut it in half. I couldn't find a mono cable, so I used a stereo, which works equally well.

Cables mounted through rubber grommets.

To more easily get the holes drilled for the components I created a paper template that I just layed on the box. Then it was easy to mark the holes in the plastic.

 

 

 

A paper template for the holes needed and the components that will be mounted in the holes.

With the holes drilled and the components mounted in the holes, it's time to heat up the soldering iron. I used the legs of the resistors to connect the switch buttons together.

Components mounted, resistors put in place and everything soldered together.

When everything is connected, test that all channels works, and then just screw the cover on the box back on. To give it the right looks, add some scalextric logo =)

Here's my finished autopilot box.

The finished controller box with a scaley logo taped on it for better looks.