Circular saw - please help identify circuit - Page 1
Forum section: electronics / beginners

author: rthorntn
author_rank: Frequent Contributor
timestamp: June 17, 2018, 08:23:24 am
content: Hi,Please help if you can.The AC circular saw isn't working, just a buzzing sound from this board, trying to figure out what the board is, the yellow component is mpx40/100/21 safety? capacitor, a soft start maybe?I replaced this circular saw already but was thinking of using the guts of this one in a router table.Thanks.Richard

author: Kleinstein
author_rank: Super Contributor
timestamp: June 17, 2018, 08:54:20 am
content: There are several possible electronic functions for a circular saw: it could be a soft start/ inrush current limiter, it could be RPM control, it could be an electric break or also a circuit to prevent the saw to start if the plug is inserted with the switch in on position.The yellow cap could be there as a capacitive dropper to power the electronics.It might help to know what type of saw it is. Especially the motor type (induction or brushed).

author: rthorntn
author_rank: Frequent Contributor
timestamp: June 17, 2018, 09:29:34 am
content: Thanks it's a DS2300 rebranded jobbie, I found a manual and it has the attached diagram in thereIt says it has soft start and overload protection.In the diagram what's the component at the far end of the red, yellow & white wires, a triac (on the unit those 3 wires go in to the motor area)?The components are surrounded in resin.

author: SeanB
author_rank: Super Contributor
timestamp: June 17, 2018, 10:12:42 am
content: Yes it is a triac. My guess is that the yellow capacitor is a dropper for powering the overload/soft start, and it has degraded from noise to the point where it no longer can power the overload circuit. Probably a 1uF part, and probably has degraded to around 200nF with the spikes it has to handle.To check connect the upper blue to the upper black wire on the module, and the lower brown to the lower black wire, and turn it on. Careful, this will kick a lot on power on, as there is no longer soft start, but will prove if the controller module is failed. you probably can depot the capacitor if the potting compound is a soft type, but if it is a hard type then you need a new module.

author: rthorntn
author_rank: Frequent Contributor
timestamp: June 17, 2018, 10:28:34 am
content: Thanks, the potting compound is rock solid.As I'm converting it to a table saw if possible, can somebody please suggest a nice quality external replacement for the circuit, is it a motor soft starter?Why is the triac located away from the other electronics, deep in the motor area, I can't even see it?

author: cowana
author_rank: Frequent Contributor
timestamp: June 17, 2018, 10:39:45 am
content: Quote from: rthorntn on June 17, 2018, 10:28:34 amThat'll most likely be for thermal reasons. The triac will generate heat, so I suspect they've bolted it to part of the saw's metalwork (to dissipate the heat), rather than having it by the control board.

author: SeanB
author_rank: Super Contributor
timestamp: June 17, 2018, 10:53:11 am
content: If you are mounting it in a router table you can just remove it, the soft start is there so it will not pull out your hands when you are holding it freehand, but when sitting rock solid in a table it will have nowhere to go when you turn it on.