Treadmill blows fuses - Page 1
Forum section: electronics / repair

author: newtothis
author_rank: Contributor
timestamp: April 03, 2018, 02:59:20 pm
content: Hi, I recently bought a broken treadmill on a wimp - it didn't power on one day - and thought i could fix it  - I couldn't but maybe you can help ?When power was added my house fuse 10A blow - after changing the house fuse (to a 13A) the internal fuse (10A) keeps blowing immidiately on the PCB even with everything disconnected.What i checked myself.Im pretty sure there is a short somewhere as there is only 2ohm restance between the 2 AC inlets on the board - and I Think it must be a component as the board seems good I pretty much tested all components.There is a varistor on the board which is desoldered and checked (>megaohm resistance)a NTC thermistor in series with the AC fase is 2 ohm at ambient temp this is the source of the resistance between the 2 inlets the NTC is oone of the first components after the fuse.There is 2 bridge rectifiers one for the motors and one for the control.They seem to be in order with diode check.Ac fase to positive = beepsAc fase to negative = no beepAC2 to pos. = beepAc2 to neg = no beepPos to neg = no beepNeg to pos = beepRelay seems to be NO and not fused.Capacitor is not a shortResistor is the expected range.I would gues that the short should be at or before the bridge rectifiers but i do't know what to check anymoreSendt fra min SM-G900F med Tapatalk

author: james_s
author_rank: Super Contributor
timestamp: April 03, 2018, 07:07:15 pm
content: Usually there is a triac or SCR that controls the motor, it could be mosfets, I would check those next. Actually just check every semiconductor you can find. If you really get stuck you could try connecting it to a current limited DC power supply set to a couple hundred mA and poke around measuring voltage, the resistance of the traces can be enough to tell where the short is.

author: Assafl
author_rank: Frequent Contributor
timestamp: April 03, 2018, 09:35:55 pm
content: There is typically a safety SCR that shorts the motor to brake it (when the safety latch is pulled the belt brakes immediately). These fail shorted so it may be what you are seeing.

author: newtothis
author_rank: Contributor
timestamp: April 04, 2018, 08:31:58 pm
content: Thank you for the replies - I will test the triacs/SCR as well.I would like to clarify that the fuse blows when the board is completely disconnected from the motors, control panels, lcd and only the AC connected. etc.Sendt fra min SM-G900F med Tapatalk

author: newtothis
author_rank: Contributor
timestamp: May 16, 2018, 06:42:13 pm
content: Ok so I finally got around to buy a new solder tip (the old one was so bad it hurt) and poked around and finally found and repaired! the issue - the smaller of the bridge rectifier had a full short - desoldered the bridgerectifier and added a new rectifier with 4x1N0007 soldered on the backside. The treadmill works as a charm I'm a little uneasy in repairing AC, but i made sure there is no solder bridge etc. and covered everything with hot glue so i hope this insulate Finding the issue was quite a journey although I actually think it was quite obvious in hindsight  anyways you wanted to give an update and thanks for the helpSendt fra min SM-G900F med Tapatalk

author: Shock
author_rank: Super Contributor
timestamp: May 17, 2018, 12:46:58 pm
content: Good work. Avoid generic hot glue unless you need to. It's not used for insulation in electronics more to prevent mechanical stress. If you do use it (and especially on power supplies) it's better to get high temp glue designed for the purpose.