Circuit board.. leg missing of timer? - Page 1
Forum section: electronics / beginners

author: mw52563
author_rank: Contributor
timestamp: April 24, 2020, 03:04:56 pm
content: HiHoping someone can help.. Im trying to fix a treadmill circuit board. Ive checked all the components I can remove and they seem ok. I was just looking through the board and one of the legs seems to be missing... i assuming its a little timer but I dont really know. Ive included a photo below. Also theres a hole in one of the runs between a rectifier and a relay.Thanks for any helpMike

author: Manul
author_rank: Super Contributor
timestamp: April 24, 2020, 03:22:53 pm
content: Not sure, looks like a mosfet to me. Can you read part number? Anyway, missing leg and slight burn mark does not seem normal.

author: Wimberleytech
author_rank: Super Contributor
timestamp: April 24, 2020, 05:38:15 pm
content: Quote from: Manul on April 24, 2020, 03:22:53 pmMOSFET theory makes some sense. Looks like a diode shunting two of the pins...fat circuit traces. Could be a snubber diode. Is there a coil connected to either of those nodes?

author: mw52563
author_rank: Contributor
timestamp: April 24, 2020, 05:44:26 pm
content: Thanks for the replies... this is the board zoomed out a bit

author: Manul
author_rank: Super Contributor
timestamp: April 24, 2020, 06:10:52 pm
content: But why we guess? There should be something written on the part. Can you try to clean and read with magnifying glass?

author: mw52563
author_rank: Contributor
timestamp: April 24, 2020, 06:16:13 pm
content: hiIve cleaned it all off, i cant see anything on it

author: Manul
author_rank: Super Contributor
timestamp: April 24, 2020, 06:37:56 pm
content: Are red marked pins all connected together? Can you check with ohmmeter?

author: WattsThat
author_rank: Frequent Contributor
timestamp: April 24, 2020, 06:44:43 pm
content: It looks like the electrolytic capacitor that you removed has spewed its corrosive liquid onto the board and it has destroyed pin 4 of that IC, probably the the original failure mode. At a minimum, you’ll have to figure out what the part number of the damaged IC is and replace it. You also need to clean up the mess from the capacitor and replace that as well.The hole in the middle of the silver trace is there by design, it’s called a via and it connects the copper on one side of the board to the copper on the other side.

author: Manul
author_rank: Super Contributor
timestamp: April 24, 2020, 07:16:03 pm
content: My guess it is mosfet or LDO. More likely LDO. So if there are no numbers visible with any light angle, the only option is to compare with typical SO-8 LDO or mosfet pinouts, trace PCB a bit, confirm and choose a replacement.

author: AVGresponding
author_rank: Super Contributor
timestamp: April 25, 2020, 09:13:16 am
content: Quote from: WattsThat on April 24, 2020, 06:44:43 pmProbably, there's certainly been some liquid contamination, from the visible tide marks.The component is marked "U6" so it's not going to be a plain transistor, though I suppose it could be a multiple transistor package.It's clearly the motor inverter power section we're looking at, but without a bit more info, more than that is just guesswork.