Trying to Repair Dishwasher Power Supply - Page 1
Forum section: electronics / repair

author: DarkZero
author_rank: Regular Contributor
timestamp: July 03, 2015, 11:36:31 am
content: Hey All!Power supply of my dishwasher isn't working and i tought it will be str8 forward to fix it but i was wrong. i powered 7805 regulator with 8V and boadr works so switcher must be wrong i changed the IC, resistor, diodes, but i got diodes bias wrong and fried the IC. i did "reverse engineering" and still cant figure out how those diodes should go are they just inductive spiking protection or clamping or what ?

author: BradC
author_rank: Super Contributor
timestamp: July 03, 2015, 12:54:35 pm
content: Are you *really* sure they were 1N4007 ? That looks like a flyback switcher and without high speed diodes nasty things will probably happen.

author: DmitryL
author_rank: Regular Contributor
timestamp: July 03, 2015, 12:56:36 pm
content: What prevents you from downloading a datasheep to this IC (LNK306 ?) and looking into it?The board will correspond to typical schematics from DS to 99.9%.BTW, replacing ultra fast diodes with something like 1N4007 may give you some funny moments.

author: amyk
author_rank: Super Contributor
timestamp: July 03, 2015, 01:08:28 pm
content: Be careful, that is a non-isolated buck converter so your schematic is wrong; apart from that, the diodes are also backwards.

author: DarkZero
author_rank: Regular Contributor
timestamp: July 03, 2015, 01:14:26 pm
content: Hey all!i downloaded the datasheet, datasheet uses inductor's rather then transformer and mentiones nothing about those 2 diodes i marked with "?" also i think diode after the 22ohms resistor shouldn't be fast diode because its 50hz all of the rest diodes i used UF1007 which are ultra-fast 1A rectifier diodes.diodes i marked with "?" the way i draw them blew the IC and when i draw the circuit i saw i biased them wrong and im not sure whats the purpose of them and how to bias them correctly.schematic is drawn from actual board im 100% sure its correct besides 2 diodes that i marked with "?"

author: mij59
author_rank: Frequent Contributor
timestamp: July 03, 2015, 01:23:19 pm
content: The upper diode is a zener diode, the lower diode should be the other way round, or visa versa.

author: DarkZero
author_rank: Regular Contributor
timestamp: July 03, 2015, 01:25:41 pm
content: @mij59so it will work without them its just some kind of protection ?

author: madires
author_rank: Super Contributor
timestamp: July 03, 2015, 02:02:10 pm
content: Quote from: DarkZero on July 03, 2015, 01:25:41 pmYou need them to limit the flyback voltage. Otherwise the filter cap and the switcher won't survive for long.

author: mij59
author_rank: Frequent Contributor
timestamp: July 03, 2015, 02:09:03 pm
content: It dissipates the energy stored in the stray inductance, it is essential for the operation.

author: DarkZero
author_rank: Regular Contributor
timestamp: July 03, 2015, 02:39:51 pm
content: Any idea what zener and second diode i should use ?

author: BradC
author_rank: Super Contributor
timestamp: July 03, 2015, 03:06:32 pm
content: Quote from: DarkZero on July 03, 2015, 01:14:26 pmIf your schematic is even close then that "transformer" is a coupled inductor.

author: mij59
author_rank: Frequent Contributor
timestamp: July 03, 2015, 03:11:23 pm
content: Where are the original diodes ?For the diode the UF1007 should be fine, the zener might actually be a transzorb, clamping voltage to be determent.

author: DarkZero
author_rank: Regular Contributor
timestamp: July 03, 2015, 03:20:11 pm
content: @mij59they both blew originally and i couldn't figure out markings on them

author: mij59
author_rank: Frequent Contributor
timestamp: July 03, 2015, 03:31:09 pm
content: In the schematic of the LNK406 a 1.5KE200A is used, link herehttp://www.codico.com/fileadmin/downloads/Akt/PI_ZI_IntegrierteSchaltregler_LinkSwitchPH.pdfThe maximum drain source voltage of the LNK306 is 700 V, assuming about 325 V dc input voltage the max. drain source voltage would be 525 V.Just guessing, may be a matter of trail and smoke.

author: DarkZero
author_rank: Regular Contributor
timestamp: July 03, 2015, 04:26:52 pm
content: @mij59well guess ill give a 200v TVS diode a try, arranged as in the data sheet u linked i bought 4 lnk306 IC and will disconnect MCU from circuit so i dont fry the thing wish me luck !

author: mij59
author_rank: Frequent Contributor
timestamp: July 03, 2015, 04:45:13 pm
content: Quote from: DarkZero on July 03, 2015, 04:26:52 pmShould work, anyway best of luck.BTW if you put your country flag in your profile, I know in which direction to look for smoke signals.

author: DarkZero
author_rank: Regular Contributor
timestamp: July 05, 2015, 06:40:50 am
content: It doesn't do anything325V goes to the D pin and nothing.meh since its a dishwasher lots of free space there ill put external transformer diode bridge and connect it directly across that secondary filter cap but it would be nice if i fixed iti'm lazy and i need dishwasher it calls for some bodging !@mij59sorry to disappoint you i just couldn't make it smoke this time, lots of fails on this one!

author: mij59
author_rank: Frequent Contributor
timestamp: July 05, 2015, 07:15:33 am
content: Quote from: DarkZero on July 05, 2015, 06:40:50 amThat's very strange , whats the voltage on the source ?Did you replace the LNK306 ?Check for bad solder joints or blown copper traces.Or use a wall wart 9 to 12 V DC should work just fine.If using a external transformer you may need to increase the value of the filter cap.

author: Psi
author_rank: Super Contributor
timestamp: July 05, 2015, 10:04:11 am
content: Is that from a F&P dishdraw? It looks like a similar PCB style to F&P stuff.It's quite sad the F&P have got so crap in the past 10 yearstheir stuff used to be good

author: DarkZero
author_rank: Regular Contributor
timestamp: July 05, 2015, 03:44:57 pm
content: @mij59voltage on source is 0v all sources are connected to 400v cap - pole@PsiIts actually bosch which imo is decently built but i doubt they make their own elektronic controlalso i noticed that its not isolated power supply if i use transformer to power 7805 are there going to be problems considering 7805 gnd pin is connected to hot gnd and i think it has to be because of the triacs

author: mij59
author_rank: Frequent Contributor
timestamp: July 05, 2015, 05:05:16 pm
content: Quote from: DarkZero on July 05, 2015, 03:44:57 pmIf you power the 7805 and leave the rest of connections intact, it should work.The LNK306 circuit has only a few components , did you test the capacitors ?Maybe the 100uF connected to BP pin has shorted, the voltage across the capacitor should be 5.8 V.Or maybe the 100uF capacitor has lost its capacity.

author: DarkZero
author_rank: Regular Contributor
timestamp: July 06, 2015, 09:47:18 am
content: @mij59yep tested all components i even checked with scope the damn thing just wont oscillateanyway i appreciate your time big thanks ! althought i didn't fix original circuit i bodged it machine works but im not happyits just a simple little circuit and i failed at that ... i ended up using 8v transformer with bridge rectifier.

author: mij59
author_rank: Frequent Contributor
timestamp: July 06, 2015, 10:58:56 am
content: Quote from: DarkZero on July 06, 2015, 09:47:18 amWell at least you don't have to do the dishes, so success at last.Probing with a ground referenced oscilloscope ?

author: Psi
author_rank: Super Contributor
timestamp: July 06, 2015, 11:31:49 am
content: As far as im concerned a dishwasher PCB should be in a water tight container with IP rated connectorsUsing gold/silver fingers on the edge of the PCB to save on the price of a connector is moronic. Steam is going to find its way in the eventually and kill the pcb.

author: DarkZero
author_rank: Regular Contributor
timestamp: July 08, 2015, 09:15:59 pm
content: yes its a ground referenced scope but i have differential probes, i know that whenever positive cycle comes trough to negative lead of the scope would be earth grounded and trigger FID breaker. guy sold me 475A oscilloscope with all the probes and stuff for 30 euros hes 70 he just asked me to keep it working