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. | |
Saturday, 23 May 2009
Repairing Sangamo Weston Master V
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.
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.
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