21-02-2025, 11:28 AM
This Greenwood fan went into continous running, even when the light switch was put to off. It happened after a Halogen bulb failure (now replaced with an LED type) on the same circuit.
The fan, with after use run timer, uses a 4060 14 stage ripple counter and oscillator chip. The chip is powered by a simple transformerless supply from the Live input.
The oscillator is a couple of gates with feedback via a CR network. The resistor includes a potentiometer which allows a variation in how long the fan stays on after the light switch is turned off. The counter stages extend the basic oscillator frequency and the Q14 output swiches a 8906 thyristor to control the fan.
When the light is on, with the light switch in the ON position, the counter is being continually reset with the Q14 output low and the fan running.
When the light switch is turned off then the oscillator, which is running, provides input to the counter stages until Q14 goes high . This turns off the fan and stops the oscillator via D2.
Checked a number of components and then changed the 4060 ‘chip’ which got the fan working properly again.
Just in case we get a few ‘noobies’ on the site do not ‘work’ on this type of circuit direct from the mains supply. It definetly needs the use of a mains isolating transformer.
My way of removing the 4060 device was to first clean the solder pads with IPA or Cellulose thinners to remove the conformal coating. This makes the pads heat quicker, with the iron, as too much prologed heat can make them come loose. Then using a pair of flat cutters, with ground down tips, cut off each leg from the chip. Now its a simple matter of hanging a pair of small forceps, on each pin in turn, and turning the PCB over and melting its solder.
Gary
The fan, with after use run timer, uses a 4060 14 stage ripple counter and oscillator chip. The chip is powered by a simple transformerless supply from the Live input.
The oscillator is a couple of gates with feedback via a CR network. The resistor includes a potentiometer which allows a variation in how long the fan stays on after the light switch is turned off. The counter stages extend the basic oscillator frequency and the Q14 output swiches a 8906 thyristor to control the fan.
When the light is on, with the light switch in the ON position, the counter is being continually reset with the Q14 output low and the fan running.
When the light switch is turned off then the oscillator, which is running, provides input to the counter stages until Q14 goes high . This turns off the fan and stops the oscillator via D2.
Checked a number of components and then changed the 4060 ‘chip’ which got the fan working properly again.
Just in case we get a few ‘noobies’ on the site do not ‘work’ on this type of circuit direct from the mains supply. It definetly needs the use of a mains isolating transformer.
My way of removing the 4060 device was to first clean the solder pads with IPA or Cellulose thinners to remove the conformal coating. This makes the pads heat quicker, with the iron, as too much prologed heat can make them come loose. Then using a pair of flat cutters, with ground down tips, cut off each leg from the chip. Now its a simple matter of hanging a pair of small forceps, on each pin in turn, and turning the PCB over and melting its solder.
Gary
