treadmill motor control board - Page 1
Forum section: electronics / repair

author: clucas
author_rank: Contributor
timestamp: April 18, 2018, 01:13:53 am
content: Hi everyone, sorry to start my first post with a repair question but I urgently need a little info.I have a motor control board from a Sportsamico brand treadmill with two blown mosfets IRFP460 and their gate biasing resistors. The resistors really smoked up and I can not read their values. One fell apart as I removed it from the board, the other I carelessly took my eye off it momentarily when on the workbench and it ran away and hid. I can't find it anywhere. It is resisting being measured.They are located at R25-1 and R25-2. I can not find a parts list or circuit diagram. The board is made by Shanghai electronics way. Pictured is a similar board with the same issue. It has a couple of irrelevant minor differences but for all intent and purposes is exactly the same just a different version. The resistors are behind the mains cap between the bridge rectifier and mosfet and can't be seen. Any help is really appreciated.

author: Chris56000
author_rank: Frequent Contributor
timestamp: April 18, 2018, 03:57:06 am
content: Hi!I think there's all sorts of literature floating about to help you calculate MOSFET driver–circuit gate components, but from my experience with monitors and PSUs, etc., A series resistor of 10 R and a gate zener (if one is used) of 15V, 500mW with the cathode to the gate is a useful starting point!Have a read of Peter Lenk's book, "Practical Design of Switcing Power Supplies" for useful design tips– I think there's PDFs of this to be ferreted out somewhere!Chris Williams

author: clucas
author_rank: Contributor
timestamp: April 18, 2018, 10:23:56 pm
content: yes I realize there are other ways I could find the info but I thought I would try here first since I need the information quickly and since this is an electronics themed site and this is a repair thread and hoped someone may have been down the same path. Thanks for taking the time tho and offering some useful information. I'll check out the book when time permits.

author: james_s
author_rank: Super Contributor
timestamp: April 20, 2018, 05:57:04 am
content: Try 10R, it's usually not critical. Most of the time whatever drives the mosfets will have blown too though, unless it has transformer isolated gate drive it will usually have a cascading failure.

author: clucas
author_rank: Contributor
timestamp: April 20, 2018, 10:29:38 am
content: yeah I'm kinda worried that might be the case James but everything I check is fine. I've heard if the treadmill belt has a problem running smoothly it will put a strain on the motor which in turn stresses the control board and takes out the mosfets. I'm going to fire it up tomorrow and let it run for a few secs b4 checking for excessive heat on the fets. The belt seemed fine when I ran the motor independently and the motor was smooth and quiet.I've found the value, it's a metal film 22R,1/4W,+/-1% tolerance. I've upgraded to 1/2W and hope for the best. Cheers.

author: james_s
author_rank: Super Contributor
timestamp: April 20, 2018, 06:30:11 pm
content: I don't know that upgrading the resistors is necessarily going to help, if the mosfets fail the resistors will still burn up, and the resistors failing quickly may have prevented additional damage.

author: BurningTantalum
author_rank: Frequent Contributor
timestamp: April 22, 2018, 10:03:45 am
content: Don't forget to give the underside of the belt a good long blast of silicone spray, along all its length, once you have repaired the fault.BT

author: clucas
author_rank: Contributor
timestamp: April 30, 2018, 11:31:07 pm
content: that's a given BT, I'll probably remove it and clean the rollers first tho.James is on the money, the fet drivers are also blown and looks like a number of other components. It's on the back burner for now. I'll update at some point in the future when it's up and running. Cheers.