Hi,
Earlier I posted a question about compatibles to mosfet BUZ71 and since the response was so good, I feel free to post a next question closely connected to this subject.
It concerns a fruitmachine that does not want to pay out; not a very popular toy for most people I can assure you.
Everything seems to work fine apart from the hopper, which is a little container with coins and a wheel in the bottom with holes in it. If the wheel turns, it kicks out coins that are counted on exit with some opto electronics (LEDs). The whole assembly contains a little printed board with 4 pins of which two pins are for 24V DC. If I connect a 24DC battery charger (400mA) to these pins the motor runs happily. It seems the motor is started by a little mosfet and a relay on the printed circuit in the hopper assembly. Resistance between the mentioned two pins is about 3 kΩ. (the relais hasn't switched then)
The control of the motor is situated on another circuitboard, which contains of a few big caps, a regulator ( converts 35V ac to DC) and 4 channels of drivers(BUZ71). One channel controls the hopper motor and has got a blown BUZ 71 mosfet. One would expect a short in the hopper assembly, but I can't find it. I swapped the blown mosfet with BUZ11 which would not switch on with 5V on the gate and 35V on source.(BUZ bust probably) Swapped it for a brandnew RFD14N05L. It exploded and caught fire the second it was turned on.
Now I am stumped; this mosfet (RFD14N05L) switched up to 14 amp at 50V, how can that be blown by a motor running fine on 400 mA? It feels to me it has to be a short but why the hell can't I find it. This MOSFET drives only 2 pins on the board and they don't short when I measure. Of course the motor relais hasn't switched because I can't measure under live conditions. But the hopper assembly runs fine when I connect it to external power.
I just don't see what I am overlooking and am doubting the MOSFET (RLD14) was up to the job, but also hesitate to put another MOSFET in again, because I haven't found a reason for failure of both MOSFETS.
Can anybody give me a push in the right direction, even after this long story.
TIA
Gerard
Earlier I posted a question about compatibles to mosfet BUZ71 and since the response was so good, I feel free to post a next question closely connected to this subject.
It concerns a fruitmachine that does not want to pay out; not a very popular toy for most people I can assure you.
Everything seems to work fine apart from the hopper, which is a little container with coins and a wheel in the bottom with holes in it. If the wheel turns, it kicks out coins that are counted on exit with some opto electronics (LEDs). The whole assembly contains a little printed board with 4 pins of which two pins are for 24V DC. If I connect a 24DC battery charger (400mA) to these pins the motor runs happily. It seems the motor is started by a little mosfet and a relay on the printed circuit in the hopper assembly. Resistance between the mentioned two pins is about 3 kΩ. (the relais hasn't switched then)
The control of the motor is situated on another circuitboard, which contains of a few big caps, a regulator ( converts 35V ac to DC) and 4 channels of drivers(BUZ71). One channel controls the hopper motor and has got a blown BUZ 71 mosfet. One would expect a short in the hopper assembly, but I can't find it. I swapped the blown mosfet with BUZ11 which would not switch on with 5V on the gate and 35V on source.(BUZ bust probably) Swapped it for a brandnew RFD14N05L. It exploded and caught fire the second it was turned on.
Now I am stumped; this mosfet (RFD14N05L) switched up to 14 amp at 50V, how can that be blown by a motor running fine on 400 mA? It feels to me it has to be a short but why the hell can't I find it. This MOSFET drives only 2 pins on the board and they don't short when I measure. Of course the motor relais hasn't switched because I can't measure under live conditions. But the hopper assembly runs fine when I connect it to external power.
I just don't see what I am overlooking and am doubting the MOSFET (RLD14) was up to the job, but also hesitate to put another MOSFET in again, because I haven't found a reason for failure of both MOSFETS.
Can anybody give me a push in the right direction, even after this long story.
TIA
Gerard
