Noob fixes sit/stand desk [help] - Page 1
Forum section: electronics / beginners

author: 3dgeo
author_rank: Frequent Contributor
timestamp: March 06, 2018, 12:17:29 am
content: I edited main post to provide more informationHi,firstly I would like to thank everyone for their time and point out that I'm noob, not idiot – I know that main voltage is not a toy.My goal is not only to fix it, but to learn along the way. I spent almost 3 months analysing this board, but my knowledge is too little. I traced all paths and practically made schematic of this board (it very messy at the moment so I hidden most of the traced lines for now).Ok, lets get on it (if You missed it in thread name – it's a stand/sit table cirquit):main board gets it's 40V AC (dark/light brown, "AC1"/"AC2") from 240V transformer, transformer gets 220V power via 1,25A slow fuse from "Plug" board ("220V out"). "Plug" board gets a 7V "main board signal" form main board ("47V to ground" and "40V to ground") and turns 220V to transformer off/on.Issues began when I was moving and table had to spend a night in a vehicle at ~0C temperature.Issues:When plugging it to main voltage in most cases "plug" board (my guess "?1" element on it) and 220v to 40v transformer starts sizzling (it is'nt a burning sizzling, it's more like oscillation sizzling) and then relay on "Plug" board cuts 220v to transformer (it's normal that relay cuts power, it does that even then there's no sizzling).When "DOWN" button is pressed relay on "plug" board connect transformer to 220v, at the same time relays on "main board" turn on motors and table goes down as it should, no issues here.When "DOWN" button is released relays on "main board" turns motors off (no issues here), but then transformer and "plug" board starts to sizzle for short period of time, than relay on "plug" board cuts power and it stops (sizzling is the issue here). On "Down" microcontroler seems to work fine.When "UP" button is pressed relay on "plug" board connect transformer to 220v but nothing else, I can hear silent humming on transformer but I don't think it's an issue. Issue here is that microcontroller doesn't send commands to turn on motors relays AND it doesn't turn on both ON5247 transistors that provide power to motors through those relays (each transistors and relay has its own pin on a microcontroler).When "UP" button is released transformer and "plug" board starts to sizzle, then relay on "plug" board cuts power and it stops (sizzling is the issue here, if it sizzles long enough it will kill a fuse).Board works exacly the same even when I unplugg all sensors and motors.Sizzling it the priority cos I'm planing to change microcontroller anyway.Can anyone tell what is "plug" board purspose? Can I remove it and connect 220v directly (slow 1,25A fuse will stay).I know that this is a very poor problem description, but I can provide more information on specific parts if needed.EDIT:I soldered 220v wires directly to transformer and fuse (bypassed "Plug" board entirely) – sizzling is gone and fuse is fine, but still no "UP", guess time to replace microcontroller..."main board" (full size in the link):http://www.3dgeo.lt/files/Main_board.jpg"Plug" board (I mirrored backside and remover 220v wires in photoshop, full size in the link) :http://www.3dgeo.lt/files/Plug.jpg

author: RobertHolcombe
author_rank: Frequent Contributor
timestamp: March 06, 2018, 01:24:23 am
content: Can you confirm that the table isn't mechanically stuck by trying to raise or lower it manually?

author: Jwillis
author_rank: Super Contributor
timestamp: March 06, 2018, 01:36:50 am
content: Click and sizzle? I would check those 4 relays to see if they're working properly.

author: 3dgeo
author_rank: Frequent Contributor
timestamp: March 06, 2018, 01:57:54 am
content: Thank You both for Your reply.Quote from: RobertHolcombe on March 06, 2018, 01:24:23 amI disassembled everything, I removed actuators, removed motors from them, trust me on this – nothing is stuck and/or limits switch are not mechanically activated.Quote from: Jwillis on March 06, 2018, 01:36:50 amSizzling appears on "Plug" board, not on the main board and not when pressed, but when button is released.I checked relays with external power supply, it seems to work normally, but I'll check again, and will check if up limit switches are not shorted internally.To be honest I would like to get rid of "plug" board entirely and replace it with relay as mentioned in original post...I might try tomorrow to bypass "plug" board entirely and connect 220v directly to transformer and fuse – if then fuse blows I will know that it's main board issue.EDIT:My guess sizzling comes from "plug" board component marked as "?1", I think it's automated fuse, isn't it?I have few extra fuses, I can play more and find out where exactly it comes from.

author: Jwillis
author_rank: Super Contributor
timestamp: March 06, 2018, 07:04:16 am
content: ?1 is a interference suppression film capacitor.They suppress line noise going to and from your circuit.The one next to it is likely a relay. I can't find anything with those numbers but that's not unusual. It probably just to switch the unit on with a low power remote switch on the front panel. ?2 is a high voltage capacitor and ?3 is an inductor. More filtering and surge suppression .W04g is a 400V rectifier.What is this for? A 3D printer or CNC router?

author: 3dgeo
author_rank: Frequent Contributor
timestamp: March 06, 2018, 12:05:23 pm
content: Quote from: Jwillis on March 06, 2018, 07:04:16 amThank You, now were getting somewhere.It's a sit/stand desk circuit. Yes, H820F48CH is a relay, it is closed normally. That board gets 7V signal from main board as described in main post. It's some sort of protection signal as well, because that signal can cut power to entire unit via "Plug" board relay.I don't get this: if that signal cuts power to all unit by turning relay off, then it should cut itself as well, this should lead to oscillation... ?

author: Jwillis
author_rank: Super Contributor
timestamp: March 06, 2018, 07:24:34 pm
content: Not if its just putting it self in stand by mode.You still need a small voltage available to activate the optocouple when you press the switch that activates the small transistor beside it which completes the circuit closing the coil on the relay. If you get voltage out of that relay when you press the on switch then it should be fine there.

author: 3dgeo
author_rank: Frequent Contributor
timestamp: March 06, 2018, 10:29:55 pm
content: Quote from: Jwillis on March 06, 2018, 07:24:34 pmI just shorted relay input and output pins in "plug" board and sizzling is gone and a fuse is still happy (updated main post), but microcontroller still does not send commands to lift the table, now I'm suspecting "violet area" above microcontroller to be cause of this – there the signal which goes to "Plug" board is created and same power line goes to buttons, though buttons work fine, microcontroler gets signal when button is pressed. There are two very small what it seems a voltage regulators, few microcontroller pins goes there. Will examine those components closer tomorrow, but I think I should just scrap those boards and make my own, reuse only parts used to create power for the motors.