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.

Chipping an AUTOart Peugeot 307 WRC 2005

I found this car on eBay quite cheap, and as I had a saloon chip laying around I figured it was time to get a car to put it in.
It was a bit of a gamble as I didn't know if I could fit the chip inside it. But as I've managed to do it on a Mitsubishi from the same manufacturer, I figured I could give it a try. However, when I got the car and popped the body on it, and desperately trying to find a suitable spot for the chip, I just had to give up with the conclusion that it's not possible to fit the saloon chip without destroying quite a bit of the nice looking interior.
I had to get a one-seater chip instead and hope that it would fit...

So, today I got the F1 chip and took a new look inside the car, and this time I found a spot to mount it in! So, let's get started.

Car's body removed

 The place that I found for the chip will be just underneath the hood of the car, i.e. above the car's guide blade. In this spot, the chip can be mounted without having to do any sort of modifications to the car's body or chassis, which makes it a bit easier. The downside, on the other hand, is of course the risk that it will touch the gears on the front axle.

I begun with stripping away everything on the chassis, i.e. both wheel axles and the motor. The wheel axles have some kind of locking mechanism on top of the bearings. These have to be twisted about 45 degrees to get loose.

Remove the bearing locks by turning them counter-clockwise

To get rid of the motor, the connections to it must be soldered off.
Now with everything removed, it's a bit easier to get the work done. I started with drilling the 3mm hole for the IR LED just in front of the holder for the driving shaft's bearing.

Everything in the chassis removed and the 3mm hole for the IR LED drilled

 To get the IR LED kept in place, I added a small amount of glue,

A bit of glue keeps the IR LED in place

Next I added a bit of extensions to the motor cables, and soldered them to the chokes on the motor (the resistor-like things). I let the original cables from the guide blade to be where they were and soldered the green and yellow cable to each of them. Every solder got a bit of heat shrink tube to protect from short circuits. I added some small strips of electrical tape to protect the cables from contacting the axles. The back-side of the chip also got some tape to protect it from a metal mesh in the hood and the LEDs for the driving lights.

Everything put in place. Note the chip upside-down in the front of the car.

To get the chip to be kept as high up as possible (and hopefully not touching the gears), I added a rolled piece of tape on top of it (see picture above) which will make it stick to the inside of the hood. When I had mounted the body, I gave the chip an extra push upwards with a screwdriver through the wheel arc to make sure it really stuck to the hood.


And the final result:

The underside of the car, where the IR LED is visible.

The finished result

Fixing a Canon CA-910 battery charger

A friend of mine (and also neighbor) came by the other day. He had borrowed a MiniDV and with it, of course, a battery charger. Now, when he connected the charger to the outlet, it just "poffed" and didn't of course work after that. That's when he called me ;-)

The Canon CA-910 battery charger

What I first noticed was that there seemed to be something loose inside it, because when I shooked it I could clearly hear something rattling inside. If this something was of some kind of conducting material, then that could very well have caused the failure.

Well, nothing else to do but to open it up I have a look. And this is what I found.

The loose objects inside the charger (above the pcb).  Note the missing ferrite core on one of the coils.

It was the ferrit core of one of the coils/chokes that had split into three pieces and fallen out of the coil housing. Now, those ferrit parts are indeed conducting, and if you take a closer look at the resistor to the right of the fuse, you see that it's been burned. So this is probably what's happen.

The loose piece that short the charger.

The good news was that nothing was really damaged, because the current went straight through the fuse and blew it. However, after taking a look at the other side of the pcb, I saw this.

Track burned off due to the short circuit.

The fix was i.e. quite easy. With some quick glue the pieces was replaced where they belonged, and the PCB track gap was bridged with a piece of cable.

New fuse and the ferrite core glued into place.

A piece of cable to bridge the track gap.

After those fixes, the charger was working again! Job done =)

Reparing an Airam Cooler 262T cool box

We bought this "active" cool box to keep the food in good shape on longer car trips. The box can be used on both 12V DC and from a 230V AC outlet. The 12V side sports a voltage guard, keeping the ~60W peltier from draining the car's battery.

The Airam Cooler 262 T

The box haven't been used that much the 2 years we have owned it, but there already seemed to be something fishy with the voltage guard this summer. I didn't mind taking a look at it before our planned trip to Lapland was closing in in September.

Verifying the fault

I begun by testing it in the car, with the engine running, and as I feared the box didn't start but only complained about low battery level. I then took it inside and hooked it up to a wall outlet, and to my big surprise the same "low battery level" LED lit up. What?! Nothing else to do but to open it up and see what's going on. However, that was easier said than done, because I couldn't find any screws that kept the top part of the lid in place. I almost broke it trying to figure out how to open in, when I realized that the screws must be underneath the lid's foam gasket...

Lid screw position under the foam gasket. One screw per side.

Reverse engineering the PCBs

Inside the lid I found two PCBs (actually three, but the third one is the 230VAC/12VDC transformer). One with a couple of relays, seemingly some kind of power board, and the other with some finer electronic components.

Relay and heat-or-cooling switch PCB

Under-voltage protection and LED indication PCB

I figured that it's best to just trace the tracks on the PCBs and sketch a schema over the circuits.

Sketched schema over the power PCB

Sketched schema over the voltage sensing/illumination PCB

Nice, huh? ;)


So, I realized that relay 1 (REL1) is a switch for battery or outlet power and REL2 is the safety switch for preventing the battery from draining. The thing is that I could hear a *click* when the outlet power was connected, which meant that the REL1 worked but REL2 didn't or wasn't just energized.

Next I tried adding 12V directly on the relay coil, and it clicked, which meant that the relay was working. This also meant that some part of the under-voltage protection sensor electronics was broken.

Finding the faulty component

By looking at my schema I quickly found a transistor grounding the relay coil on signal from the comparator (IC1). By measuring the voltage on the transistor's (Q1) base I saw that it sure did get the signal comparator, but it didn't lead current through to the emitter. Ahaa! There's the problem. I then tried to short circuit the collector and emitter legs, and voila! the fans started spinning!

Faulty transistor.

I replaced the transistor with one that I found in my drawer, which had kind of the same specs, but the collector and emitter legs where switched, so I just had to turn it 180 degree compared to the original one before soldering.
Tested with both 12V DC and 230V AC power source and both now works again!

Green light and a spinning fan, the thing is working again!

Repairing a Philips Plasma TV

I was visiting my sister some weeks ago and their TV had given up. It was an almost 10 years old, first generation plasma TV which was state of the art when it was new. Now it was about to be part of the gigantic e-waste mountain the "planned obsolescence" industry and our crazy I-always-want-the-latest-gadget society generates every year. To my luck, they asked me if I wanted to have it, in case I could repair it and hopefully make use of it for still some more time. Said and done, I stuffed it into our car and brought it home.

The TV set comes with the plasma screen and a separate tuner/input box. The two are linked with a vga cable with integrated stereo audio cables with cinch connectors.

The problem they have had was that the TV had begun to take some time to start-up and after a few weeks it got worse and they had to turn it off on the power button on the side of the TV a couple of times before it kind of got warm enough to come to light up.

Fixing the tuner box

When I got home and connected everything together, it seemed to me that the tuner box didn't want to start, because the power LED did some blinking, both green and red and the ended up in an amber colour. A quick google search, and I found this thread on FixYa. Seemed that some PIP (Picture In Picture) board had a faulty fuse. One of the solutions was to disconnect the board completely, and to my big surprise the power LED did now stay green! However, now the SCART inputs didn't work. Only sound came through...hmm...however, replacing the fuse 1800 (MP40, 400mA) and re-connecting the board did the trick.

Tuner box's PIP board with "replaced" MP40 fuse.

Fixing the plasma screen

Next problem was the plasma itself. After removing a fairly large amount of screws, the back plate did finally came loose.

TV's back side.

TV with back plate removed. PSU in the middle.

The TV did take a couple of on-off cycles before it finally showed any picture. But google to my rescue! I was certainly not the only one trying to fix a similar TV. Turns out its a quite common error on these models (if not almost all plasmas) due to the high temperature they generate and is most often caused by some dried out capacitors in the PSU. On this thread at avforums.com (22 pages long!). As I read the first pages I found out that I should try to change what seemed to be the most typical caps to fail, i.e. 2662 (25V 1000 uF) 2663 and 2664 (both 50V 100uF), but without any luck.

The PSU with the caps that I canged marked.

However, on page 10, I found someone that had figured out the most fragile capacitors on the exact same model as mine. The post is found here. I marked all those caps with a marker pen and found out that the caps were in smaller groups. By using the old hair-dryer trick I quickly found out that about 5 caps in one group was failing, because when pre-heated, the TV fired up instantly! These caps (2465,2508,2540,2541) were surface mounted (except one, 2510), so it was a bit tricky to remove without destroying the PCB. Actually one of the tracks came loose, and I had to replace it with a small jumper wire. The new caps were for hole mounts, so I had to bend their pins to fit the pads on the PCB.

New caps in place.

Surface mounted caps replaced with standard ones.

When the caps were changed, the TV lit up instantly, the fix had worked!

TV stand

Next thing was to get a stand for it, because I didn't want to mount it on the wall. So a bit of carpentering, and voila! a nice TV stand. Sorry for the bad picture quality (taken with my mobile's cam in a dark room...)

TV on stand, back side.

TV on stand, front side.

Chipping an AUTOart Mitsubishi Lancer Evolution VII WRC

I finally took the time to chip my Mitsubishi Lancer Evolution VII WRC from AUTOart.

After popping the hood, this is what's revealed. What one immediately notice is that it's very little space for the chip in here (as the car is apparently not designed to be chipped). Another problem is the placement of the IR LED as the drive shaft is in the center of the car.

I started by removing all the stuff inside the car, that includes both wheel axles, engine, cables and the switch with which you can choose the polarity to the engine. I then drilled the front-most hole to suitable size for the LED.

 The problem here is that the dive shaft will short the LED's pins, so I tried getting it as low as I practically possible, however not all the way down as that could risk it touches something on the track. A bit of electrical tape on the LED's pcb should protect it from shortening...

I found that the chip itself can only be positioned on the left side of the motor and as far to the front as possible. The chip does also need to stand flat on the bottom which requires some cutting of plastic enforcement aligned with the rear-end of the motor's fittings.

 Another problem is the light's pcb in the car body. This must be cut loose in one end and bent back as far as possible to make room for the chip (see blue frame in above pic).

After this, it's just a matter of soldering all wires together and below is the result:

 Underneath you can see the IR LED between the front axle and the motor.