SAMSUNG washing machine doesn't power up - Page 1
Forum section: electronics / repair

author: DennisLoi
author_rank: Newbie
timestamp: July 08, 2023, 09:56:25 am
content: I have a washing machine that has stopped in the middle of a cycle and showed an 'UC' error. On the SAMSUNG's site it says that is 'is related to the excessive fluctuation of the power supply voltage'. I turned it off and now it doesn't turn on anymore.Analysing the main board, I've checked low voltage power supply and it seems to work, it outputs 37V (or something like that, I don't remember the exact value). On some connectors I've measured 5V and 12V.In the same board there is also a relay connected to the input that, when active, powers other components (like the door lock) and the main rectifier circuit that powers the inverter.If I bypass that, the machine turns on and after a couple of seconds I can hear the relay activating. At this point I can remove the bypass and the machine stays on. (I haven't tried to run a cycle)At this point I'm not sure on what is the problem. The description of the error code makes me think that it has something that measures some kind of voltage? (I don't know what it checks and where), so maybe that is faulty? Or I'm missing something else?I've attached a simplified schematic that I've drawn while trying to understand how it works.Moreover, I've found a service manual online that have some details on the wirings:https://www.manualslib.com/manual/2797277/Samsung-Ww6000j-Series.html

author: ramussons
author_rank: Contributor
timestamp: July 08, 2023, 12:25:48 pm
content: 2 Points.That GND cannot be ground. That will simply short that power supply bridge.Track the source of power for the Relay. How does that operate in the first place?

author: marhuum
author_rank: Contributor
timestamp: July 08, 2023, 01:31:09 pm
content: Quote from: DennisLoi on July 08, 2023, 09:56:25 amI don't get, why don't try to run operating it thenSome of such machine Uc is to mean low Voltage too, sometime just reset/clear memory would work, ie. let it powerless for a minute or so

author: DennisLoi
author_rank: Newbie
timestamp: July 08, 2023, 02:05:20 pm
content: Quote from: marhuum on July 08, 2023, 01:31:09 pmI haven' tried to run because the machine was in pieces and not properly assembled.But the main reason was that I didn't like the "hack" and even if the machine had worked I wouldn't have resolved anything because as soon as you turn off the machine, you can't turn it back on.I guess one possibility is to bypass permanently the relay but I don't like that because I don't fully understand why it's there.I hope this clarifies. Thank you

author: marhuum
author_rank: Contributor
timestamp: July 08, 2023, 02:11:50 pm
content: Quote from: marhuum on July 08, 2023, 01:31:09 pmsuspect that when the Uc happened it'd work back just by unplugging it waiting it for a minute or so

author: DennisLoi
author_rank: Newbie
timestamp: July 08, 2023, 03:04:59 pm
content: Quote from: marhuum on July 08, 2023, 02:11:50 pmAh sorry I didn't clarify it. The machine stayed off and unplugged for a couple of days. Still doesn't work.

author: DennisLoi
author_rank: Newbie
timestamp: July 08, 2023, 03:43:15 pm
content: Quote from: ramussons on July 08, 2023, 12:25:48 pmThe relay is powered from a 12V rail generated by a kia78r15pi. However the enable pin of that regulator is not active (I'm not sure who controls it as it's under an heatsink which is a pain to remove).I've forced the regulator on with a resistor and the it works. I have also confirmed that the transistor that switches the relay works.