240volt standard lamp with 12 v reading light. both dimmer controlled12 volt circuit fuses and has blown several bits of the circuit - can I rebuild it? How do I check which bit is causing the problem?
12volt circuit problem
- Thread starter aconradreed
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Apparently not.
And that's why - you'd need to start learning electronics from scratch, learn fault tracing and diagnosis techniques, buy test equipment.....
All of which would take a huge amount more time, and cost more money, than just buying a new light.
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In the old days we would have a transformer which gets some where near to 12 volt then rectify it to DC then feed it through a voltage regulator and it was just a case of moving step by step through the circuit.
However the transformer at 50Hz is not very efficient and uses a lot of copper, and the voltage regulator produces a lot of heat. So the new method is called switched mode.
With this first step is to rectify into DC feed a capacitor then turn it back into high frequency AC as a result a much smaller transformer can be used. One transformed the voltage is sampled and this alters the perimeters of the bit turning the DC into AC at input side. This is the problem as the whole process is going around in a circle so a fault anywhere will cause whole device to fail so no longer can one proceed step by step to repair.
With large units repair is done by changing whole boards but with small units it is just not worth repairing. It's a bin job.
So the "Bit" you need to change is the switch mode power supply which you will replace as one complete unit. But likely a new power supply will cost same as new lamp complete.
This lamp
has a switch mode power supply built into it. The large capacitor can be clearly seen which stores the DC before being turned into High Frequency AC we can buy whole lamp for a £1 so the only reason to open it was to take photo. We just buy new. And then have to take old one for special disposal as it contains mercury and likely arsenic plus the nasty electrolyte in the capacitor but our government seems to think these are better than tungsten bulbs!
However the transformer at 50Hz is not very efficient and uses a lot of copper, and the voltage regulator produces a lot of heat. So the new method is called switched mode.
With this first step is to rectify into DC feed a capacitor then turn it back into high frequency AC as a result a much smaller transformer can be used. One transformed the voltage is sampled and this alters the perimeters of the bit turning the DC into AC at input side. This is the problem as the whole process is going around in a circle so a fault anywhere will cause whole device to fail so no longer can one proceed step by step to repair.
With large units repair is done by changing whole boards but with small units it is just not worth repairing. It's a bin job.
So the "Bit" you need to change is the switch mode power supply which you will replace as one complete unit. But likely a new power supply will cost same as new lamp complete.
This lamp
As both BAS and ericmark have alluded, you really need knowledge, experience of electronics and some test equipment to diagnose and repair the unit. As you can imagine a comprehensive lesson in electronics is beyond the scope of this forum and most likely the circuit is beyond economic repair anyway. The dimmer circuit (assuming quite modern) probably contains (amongst other components) a TRIAC which is a sort of semiconductor AC switch that turns on and off at defined points in the AC cycle allowing the energy delivered to the lamp to be controlled/varied. The general process is often called phase angle control. The circuit can be sophisticated or quite simple but either way requires knowledge of the electronics.
It does unfortunately sound like the lamp has reached the end of its serviceable life
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View media item 35253If it's this type of lamp, as everyone else has said it's not worth fiddling with.
I tried once, for a 'friend' - waste of time. They only cost £30ish.
I saw that thing in war of the worlds.
The 1953 original
The 1953 original
It put up a good fight but in the end it lost the war........
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