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| saaluc:
--- Quote from: inse on December 27, 2024, 03:08:54 pm ---I think timeandfrequency and me are trying to get an answer to the same question: where is the return path of the gate current to the microcontroller? If you have 4.8V both at the uC and the gate vs. GND but nothing between gate and cathode, the problem must be in this loop. --- End quote --- To solve this problem, how can I help? Is it helpful to mark the paths between microcontroller and gate on the picture and upload it for you? |
| inse:
Get a continuity tester and draw the schematic of the SCR drive, there seem to be more components involved. For example what are the diodes around the SCR for? |
| timeandfrequency:
According to the parts we see on the board, and what you explaned, the gate drive should be rather simple : there's no optocoupler, no ZCD, no pulse transformer. The additionnal diodes need more investigation. But clearly, there's no isolation: the µC is directely connected to live voltage. A very common principle used in many appliances. I agree with @inse : we do not understand how you can have 4.8 VDC when you say : pin No. 7 of the MCU is connected (through a resistor and a diode) to the Gate of the SCR; and at the same time you have no voltage at the gate, because you wrote : I put the negative probe of the multimeter on the Gate of SCR, and the positive probe on the Cathode of the SCR, there is no voltage (0.000). Between MCU and SCR, there must be a direct path and a return path : the curent flows into the gate only if there's a circuit/loop : if there's no circuit, no SCR firing can occur. Also check the diode and the resistor in the gate path (coming from the MCU). Yes the TNY612 is an SCR (also named 'Thyristor') and it's legs are named K, A & G. It's a standard part and to be fired, it needs VGT = VGK > 1,3 VDC and at least 2 mA of current injected. |
| saaluc:
The diode and the resistor in the gate path (coming from the MCU), are OK. |
| saaluc:
--- Quote from: timeandfrequency on December 27, 2024, 04:08:47 pm ---According to the parts we see on the board, and what you explaned, the gate drive should be rather simple : there's no optocoupler, no ZCD, no pulse transformer. The additionnal diodes need more investigation. But clearly, there's no isolation: the µC is directely connected to live voltage. A very common principle used in many appliances. I agree with @inse : we do not understand how you can have 4.8 VDC when you say : pin No. 7 of the MCU is connected (through a resistor and a diode) to the Gate of the SCR; and at the same time you have no voltage at the gate, because you wrote : I put the negative probe of the multimeter on the Gate of SCR, and the positive probe on the Cathode of the SCR, there is no voltage (0.000). Between MCU and SCR, there must be a direct path and a return path : the curent flows into the gate only if there's a circuit/loop : if there's no circuit, no SCR firing can occur. Also check the diode and the resistor in the gate path (coming from the MCU). Yes the TNY612 is an SCR (also named 'Thyristor') and it's legs are named K, A & G. It's a standard part and to be fired, it needs VGT = VGK > 1,3 VDC and at least 2 mA of current injected. --- End quote --- Can you set aside or ignore those two test that I have done (The pin No. 7 of the MCU is connected (through a resistor and a diode) to the Gate of the SCR; this pin and the Gate have 4.8 volts, even if I have not pushed the on/off button of the device. I put the negative probe of the multimeter on the Gate of SCR, and the positive probe on the Cathode of the SCR, there is no voltage (0.000)) and independently guide me diagnose the fault(s) of this device? |
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