Repairing Canon EF 28mm

A common fault on the Canon EF 28mm series of lenses in the zoom jamming, this is easy to fix but the rear of the lens had to be removed and a very fragile connector de-soldered and removed from the PCB. Once this has been done just back off then tighten up the big screw to fix.

Topfield TF5800PVR Power Supply Repair

A common fault on these units is the protection diodes on the HDD going short circuit and blowing the diodes on the output side of the SMPS board. This happened on mine which killed D8 and U51 (on the main board) - you can find some very useful info on common problems here.

Building a (Child-Proof) Multi-Touch Table

Some pictures of a multi-touch tabletop in development, using DI with a toughened frosted piece of glass for the top and the frame from a school table. Using a 2 mirror setup with a Benq short-throw projector and two PS3 Eye cameras with IR filters.

 

LIS302DL - Triple Axis Accelerometer

The LIS302DL is a triple axis I2C accelerometer that you can buy on a breakout board produced by Sparkfun pretty cheaply and is ±2g/±8g selectable. Its is easy to hook it up to an Arduino (SCL - analog pin 5, MOSI - analog pin 4, tie MSIO to VCC for I2C address 29 or gnd for 28).

There are a few handy examples to get started quickly, such as this and this. I had better readings when I turned in the internal filter.

Repairing Sangamo Weston Master V

The old Sangamo Weston Master light meters seem to have a bit of a cult following with the most desirable being the Weston Master V and the Euro-Master (which is still being made!). These are now 40/50 years old most of them are still working fine. All versions of the meter use a selenium cell so no batteries are needed and they seem to stay in reasonable calibration. I was given a Weston Master II in which the meter mechanism was beyond repair but it seemed like such a cool little device I bough a Weston Master V second hand. This turned out to be broken too so I decided to take it apart to have a look. To take these meters apart you need some fine needle-nose pliers and some small side cutters (for gripping the odd shaped screw heads). Firstly you need to unscrew the two hex shaped screws that hold the alloy plate to the back. Once this is off the little door on the back for high/low range comes off. Next unscrew the knurled part in the middle of the dial on the front. Now you can access the two nuts that hold the front on. Once the front it off you can see how everything works.

The cell is sandwiched between a circular copper contact (attached to the single flexible wire you see running under the meter mechanism) and a large sprung metal contact. A stiff wire that runs from near the upper range limiter on the meter to near the scale mechanism completes the circuit. A sprung bar presses on the needle to prevent it moving until you press the button on the side. In the case of my meter the cell had died. To get the cell out you have to take the whole thing apart which is easier than it sounds. I forgot to take any pictures at this point but you simply remove the meter mechanism then keep unscrewing the odd nut/bolt pieces (remembering the order in which everything came out) until you get to the cell. I put in the cell out of my dead Weston Master II and this seemed to work fine, I also cleaned all the contacts etc. The calibration seems pretty good after zeroing it. Most of the internal nuts were loose when I removed them - this seem to be a common problem that stops the meters working. To complete the circuit from the sprung metal contact on the cell to the meter mechanism relies on 2 bolts being on tight. Putting it back together is pretty easy apart from locating the ends of the springs from the door on the back into the holes in the moving part of the scale mechanism.

Shopping for a Renault Megane Scenic...

For a cheap and practical family car a Megane Scenic is pretty hard to beat. They have been around for ages and being really popular finding a decent second hand one should be easy. Being a French car they do have some interesting foibles. From doing a bit of research and test driving an apparently "immaculate" example I discovered some pretty important things to look for when buying one.

Alarm/Immobilizer The Immobilizer is integrated into the ECU and activated via a IR dongle in the key. To replace one of these keys the cost is ~£125 from a Renault dealer. As the immobilizer is integrated into the ECU is cannot be removed but can be deactivated by entering a 4 digit code (every time you turn on the ignition) using a button on the dash. You can get the code from a Renault dealer for ~£30 or various sources online for free. It seems you can get electronic devices that you can wire in that enter this code for you automatically for about £80. If the remote fob doesn't work its batteries could be flat, the fob could be dead, the fob could need re-syncing with the ECU or the IR receiver may be dodgy. A common fault is water ingress into the IR receiver built into the unit near the front courtesy light (water comes through the base of radio aerial which sits above it). Sometimes this can be dried out and sealed, and new unit is £60 from Renault. There is plenty of info online about immobilizer problem and they seem very common. Without 2 working fobs its potentially going to cost lots of time and money.


Engine It seems engine are generally reliable but prone to oil leaks. The timing belt needs changing (petrol engine) at 60,000 miles. They are prone to headgasket failure if the coolant is not changed regularly and kept topped up (as all French engines are). The expansion tank should be free from a coating of red/brown sludge on the inside which indicates it hasn't been looked after and you could be in for trouble. Coolant should always be a strong blue or red color with no sign of contamination. Difficulty starting when the engine is warm is sometimes a problem and needs to be checked.

Body Work They tend to go rusty round the back wheel arches. If the arches have started going you will probably be able to find other spots of rust starting/bubbling around the car. Rust is probably to be expected on a old/cheap/French car but only gets worse with time and is a pain to sort out properly. The paint work is not of brilliant quality so expect scratches etc. French cars are notorious for poorly designed drainage channels through the body which get blocked with dirt over time and cause problems. Brake hard and listen for a sloshing sounds near the front footwells, this indicates that water has collected in the sills and they need draining/sorting out. If the blower only works on the max setting this probably means the drainage channels at the bottom of the windscreen have clogged and water has got into the fan motor (frying the block of resistors used for different fan speeds). This means taking the dash apart to fix it.

Brakes Under heavy braking the car should pull up dead straight even if you take your hands off the steering wheel. If it veers or just one wheel locks up etc then this probably means you have ceased brake calipers slider pins (or the pads are right down or there is a bigger problem with the brake system). This is a common fault on all cars and can be a pain to fix, sometimes requiring new calipers. Brakes should be responsive and take little effort to stop the car.

Misc Air con should get really cold fairly quickly otherwise it is £50+ to have it re-gassed. Turning the steering wheel from lock to lock while stationary should produce no strange noises. Pulling away in 1st with the handbrake on should be difficult otherwise the clutch is worn (or handbrake needs adjusting!). CV joints shouldn't click when accelerating on full lock. Can be problems with the cables inside the back seats for the mechanism to move them up/down so this needs to be checked.

DIY Flash Trigger Safe Sync

Most modern cameras allow a max flash trigger voltage of 6 volts (Canon) or 8 volts (Nikon). The trigger voltage runs between the 2 main pins on the hotshoe of a flash or between the pins on the trigger connector of a studio strobe, shorting these pins together fires the flash. Before digital cameras this was done using a mechanical switch attached to the shutter but now this is done electronically (hence the max voltages). Old strobes use a trigger voltage of anywhere between 12 to 350 volts and this can be checked using a multimeter set on volts DC - using anything above the 6/8v will fry or seriously shorten the life of the trigger circuitry in your digital camera. In order to reduce the sync voltage you need a 'safe sync' there are manufacturers in the US that make these but they are pretty easy (and more importantly, really cheap!) to build one yourself. The simplest one I found was http://www.repairfaq.org/sam/zpaofu1.pdf. The main advantages (compared to ones using an optocoupler) are the parts are easily available and no external battery is needed, sync voltages are reduced to ~4v using the circuit. Pretty much any triac will work, I only had 1M resistors instead or a 10M or 2 x 4.7M so my circuit is bigger than it needs to be. I hooked mine circuit up in the middle of a sync extension cable to make it really easy to use. Obviously I suggest you test the circuit just using your strobe before plugging it into your D-SLR!