| Electronics > Repair |
| Lab Technics D2012 Plus mini centrifuge board repair |
| (1/1) |
| psysc0rpi0n:
Hi. I have the above mentioned equipment and when we turn it on, it stays one for like 2 seconds and then it shuts down the power supply / transformer. So I disassembled it and one of the control boards, next to the input plug, has a circuit composed by 6 IRF9540N (pictures attached). I am not sure how the 6 mosfets work together but the middle pin of each one is connected to the middle pin of the mosfet that is above/below it. Then, one of the rows of 3 mosfets have 3 diodes connected to one of the mosfet pins. The other end of the diode is connected (if I'm not mistaken) to a resistor and a led. So, I went measure all the 3 pins of all mosfets while the equipment was ON and I got the following results. Let's say 2 rows, each row with 3 mosfets. Row 1 Mosfet 1 Pin 1 - 24.4V Pin 2 - 0V Pin 3 - 24.4V Mosfet 2 Pin 1 - 24.4V Pin 2 - 0V Pin 3 - 24.4V Mosfet 3 Pin 1 - 24.4V Pin 2 - 24.4V Pin 3 - 24.4V Then, Row 2 Mosfet 4 (connected to Mosfet 3 by middle pin) Pin 1 - 0V Pin 2 - 24.4V Pin 3 - 0V Mosfet 5 (connected to Mosfet 2 by middle pin) Pin 1 - 0V Pin 2 - 0V Pin 3 - 0V Mosfet 6 (connected to Mosfet 1 by middle pin) Pin 1 - 0V Pin 2 - 0V Pin 3 - 0V Is it likelly that the issue is on Mosfet 3 ?? It's the only one which voltage values are not the same as Mosfet 1 and Mosfet 2. Mosfet 4 middle pin is at 24.4V because is connected to Mosfet 3 middle pin, I guess, otherwise, it would also measure 0V just like Mosfet 5 and 6. Can you guys tell me anything about this with the provided information? PS: I also measure the 3 pins of all mosfets while the equipment was OFF in diode mode and all the mosfets read around 0.4V on 2 of their pins and around 1.5V on the other pin, except for Mosfet 3 that read very low values on its 3 pins! Like close to 0V. |
| Harry_22:
Hi! You are right. The Mosfet #3 is broken and should be changed. |
| psysc0rpi0n:
--- Quote from: Harry_22 on January 16, 2025, 07:45:12 pm ---Hi! You are right. The Mosfet #3 is broken and should be changed. --- End quote --- Ok, thank you for your reply. You even figured out that 3 of them are N-channel and the other 3 are P-channel. I didn't even thought about that. I remember to have worked with a battery charger controller and they also have a similar circuitry where they use like 2 rows of 4 mosfets and they work together. When one row is ON the other is OFF and vice-versa. Probably in this case something similar should be the case, no? |
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