If there is nothing between the TRIAC and motor, then there is no snubber. The snubber needs to be across MT1 and MT2 of the TRIAC. Use the values I or others have given you, but to be really safe, place a 275v MOV across MT1 and MT2 also.
Some comments for "young players" too...if you choose a TRIAC that is in a different package from the original TO-92...or even if you DO choose an equivalent TO-92 packaged TRIAC with much the same specs as the original ..MAKE SURE THE PIN OUTS ARE CORRECT...often different numbered (but electrically equivalent) devices will have different pin-outs and devices in different packages will have different pin-outs...so be aware of this. Gate firing pulses are always applied between MT1, or A1 and the Gate, so MT1/A1 will be connected to the driving logic gates chip's Vdd/GND line, (which in a non-isolated circuit such as this might well be the the Arctiv/Line/Phase of the mains...so it is only a local "GND" with respect to the electronics inside the unit, not real TRUE ground or Earth.) MT2/A2 will go to the load, (Motor).
To select a replacement TRIAC,, you need to first try to find the specs of the original. The important parameters are:-
1) Hold-off voltage, (i.e. the voltage that appears between MT1 and MT2 before the TRIAC is fired, this must be greater than the peak value of the mains....for the U.K. (same as Australia or South Africa) 230v R.M.S. at 50Hz. So the prak is 1.414 x 230 = 326 volts so choose a 400v TRIAC, (if you want a greater safety margin, choose a 600v TRIAC, but it will be more expensive)
2) Current, i.e, the current that flows through the TRIAC once it has been triggered, this will be the (instantaneous) motor current, so connect the motor directly to the mains and put a 1Ω resistor in series with it, measure the voltage drop with a multimeter on the AC volts range across the 1Ω resistor and this will be the current. Select a TRIAC with a current rating somewhat greater than this to accommodate instantaenous values during the AC cycle...but not too much greater or it may unlatch...(i.e. the holding current may be too small, look up the Wikipage on TRIACs to find out more.) So if the motor draws 500mA, any TRIAC up to 3A or so will do...try bigger ratings if you like and see if they will hold or look in the datasheets of the BTA family.
3) gate trigger current this varies dependant on the "firing quadrant"...look up the Wikipage, it explains this clearly.
https://en.wikipedia.org/wiki/TRIAC I would suspect your original TRIAC had a 10mA QII and 25mA QIV rating, so find a BTA device with the same ratings. You did say it was triggered from a logic gate, correct? Make sure this logic gate was not damaged when the original TRIAC failed...if so, or even just as a precaution, change the gate chip anyhow. Try to get a gate chip of the same brand, particularly if it is a Schmitt type, (like a 4093) as different brands can have different trip voltages.
If you don't know, or cant find the specs of the original device, make an EDUCATED GUESS, I'd say that from the application, 400v, 1A, 10-20mA Gate.
Is there a resistor between the output of the logic gate and the TRIAC's gate, if not, a good practice is to put 47-100Ω there. For extra chip protection place two diodes, one with its anode to the chip's Vss/GND rail and its cathode to the output of the chip driving the TRIAC, put a second one with its anode to the output of the chip and its anode to the chip's Vss/RAIL pin...crappy 1N4004's will suffice...if the mains then comes out the gate of the failing TRIAC, the resistor will go up in smoke and the chip will be saved by the diodes!
Some points of note...if the voltage rating of a TRIAC, (or any other power semiconductor for that matter) is exceeded, even for an instant..the device will be destroyed.
If the current rating of a TRIAC, or most other power semiconductors, is exceeded by say 50%, the device will usually handle it...it depends in how much greater the current spike is over the device's rating and for how long it lasts...the greater it is, the shorter duration and repetition frequency the device will handle, but you have some leeway with current..but NO LEEWAY AT ALL with voltage.
Other members have provided you with URL links to component suppliers and datasheets....use tham to choose the device that will solve your issue RELIABLY, so you will never need to pull those fans apart ever again!
The snubber has been deliberately left out because the accountant was leaning over the designing engineer's shoulder and whispering "sweet nothings" into his ear! Believe me, it was a very deliberate act that goes against all the rules of good, reliable design.
