Before condemning the components on the board, are you sure the motor brushes are in good condition?
Working for half a second then stopping sounds more like an overload problem than the triac.
Brian.
any easy steps for verification of thier condition?
The motor is labeled 20-240V and you can test it directly by connecting to the house power supply. It is an universal motor and hence will have highest speed when connected directly. Also check the motor body is not short with any winding (use a multimeter or a line neon tester).
Hello libyantiger,
Just out of curiosity, what are the values printed on the side of those two capacitors? (Please see modified pic below)...
Also, the slider as marked in blue; Is it a speed controller or a stepped switch?
Regards,
Relayer
View attachment 139317
The danger with bypassing the control board to see it it is faulty is that if the brushes are the problem, there is nothing to stop the motor being damaged...
OK, I'll explain as simply as possible:
The triac is like a super fast acting switch.
If you fed AC mains directly to the motor it would run at full speed. To reduce the speed there are two options, to reduce the voltage or to keep full voltage but reduce how effective it is by pulsing it on and off. The idea is if you feed it short bursts of power with long gaps between them, the average power will be low and the motor will turn slowly, if the bursts are made longer, the average power goes up and the motor goes faster. As long as the bursts occur rapidly enough, the mass of the motor keeps it spinning and you don't notice it is actually getting little 'kicks' to keep it turning instead of steady power. I just grossly oversimplified how it works but hopefully you get the idea.
The triac is what controls the bursts, the slider control adjusts the burst lengths and hence the motor speed. Technically, it's called phase control. The busts will be at a constant rate, twice the AC line frequency so they are at either 100 or 120 times a second depending upon your country's power lines being 50Hz or 60Hz.
I would still check the brushes first, they wear out over time and are designed to be replaced. Somehow the two connecting points on the motor will be removable and underneath them will be a spring and a carbon block. The block is the brush and the spring keeps it in contact with the moving part of the motor (rotor). Carbon is conductive so the power on the two wires passes down the spring and brush where it touches the rotor and feeds power to it while it is still free to spin. To replace the brushes, first get replacements, they are not expensive then open the black connecting points and pull the old brush out. Do the reverse to re-assemble it using the new brushes.
The danger with bypassing the control board to see it it is faulty is that if the brushes are the problem, there is nothing to stop the motor being damaged.
Brian.
Sometimes, at the point of complete failure, the brushes contract when cold and connect to the commutator, as soon as it starts up, the combination of heating and vibration moves one or both far away enough to break the connection. I can't be certain in this instance but I know it does happen that way. The danger of direct AC connecting is mechanical damage to the commutator if the brushes shatter or are worn down to their bases.
Brian.
If the other one is the same I would say they are OK. They get shorter as they wear down but there seems to be plenty of length left on that one.
While open, look through the hole at the commutator (copper sleeve with slots in it) and make sure it has no obvious scratches or burned sections. It turns around if you rotate the motor shaft so you can inspect it at all angles.
If the fault is still there after you reassemble it, you have an electrical fault on the circuit board. Check it for poor solder joints first, then I would suspect the capacitors with the black plastic sleeve over them. It would be extremely unlikely to be the yellow block capacitors in the red boxes on earlier photographs.
Brian.
If you reduce the voltage across the motor terminals, it will rotate slower but also take a higher current. If you increase the voltage, it will run a little faster but take a lower current. Motors get damaged because of "stalling", the rotor is stuck but there is some voltage still present (that happens under low voltage) - that makes rather high current to pass and damage the winding. Therefore my recommendation is not to reduce the voltage on the motor (than the specified) because motors get damaged under low voltage condition.
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