Author Topic: Trying to Repair Dishwasher Power Supply (Read 7310 times)

DarkZero · « **on:** July 03, 2015, 11:36:31 am »

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 ?

BradC · « **Reply #1 on:** July 03, 2015, 12:54:35 pm »

Are you *really* sure they were 1N4007 ? That looks like a flyback switcher and without high speed diodes nasty things will probably happen.

DmitryL · « **Reply #2 on:** July 03, 2015, 12:56:36 pm »

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.

amyk · « **Reply #3 on:** July 03, 2015, 01:08:28 pm »

Be careful, that is a non-isolated buck converter so your schematic is wrong; apart from that, the diodes are also backwards.

DarkZero · « **Reply #4 on:** July 03, 2015, 01:14:26 pm »

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 "?"

mij59 · « **Reply #5 on:** July 03, 2015, 01:23:19 pm »

The upper diode is a zener diode, the lower diode should be the other way round, or visa versa.

DarkZero · « **Reply #6 on:** July 03, 2015, 01:25:41 pm »

@mij59

so it will work without them its just some kind of protection ?

madires · « **Reply #7 on:** July 03, 2015, 02:02:10 pm »

Quote from: DarkZero on July 03, 2015, 01:25:41 pm

@mij59

so it will work without them its just some kind of protection ?

You need them to limit the flyback voltage. Otherwise the filter cap and the switcher won't survive for long.

mij59 · « **Reply #8 on:** July 03, 2015, 02:09:03 pm »

It dissipates the energy stored in the stray inductance, it is essential for the operation.

DarkZero · « **Reply #9 on:** July 03, 2015, 02:39:51 pm »

Any idea what zener and second diode i should use ?

BradC · « **Reply #10 on:** July 03, 2015, 03:06:32 pm »

Quote from: DarkZero on July 03, 2015, 01:14:26 pm

i downloaded the datasheet, datasheet uses inductor's rather then transformer

If your schematic is even close then that "transformer" is a coupled inductor.

mij59 · « **Reply #11 on:** July 03, 2015, 03:11:23 pm »

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.

DarkZero · « **Reply #12 on:** July 03, 2015, 03:20:11 pm »

@mij59

they both blew originally and i couldn't figure out markings on them

mij59 · « **Reply #13 on:** July 03, 2015, 03:31:09 pm »

In the schematic of the LNK406 a 1.5KE200A is used, link here http://www.codico.com/fileadmin/downloads/Akt/PI_ZI_IntegrierteSchaltregler_LinkSwitchPH.pdf

The 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.

DarkZero · « **Reply #14 on:** July 03, 2015, 04:26:52 pm »

@mij59

well 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 !

mij59 · « **Reply #15 on:** July 03, 2015, 04:45:13 pm »

Quote from: DarkZero on July 03, 2015, 04:26:52 pm

@mij59

well 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 !

Should 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.

DarkZero · « **Reply #16 on:** July 05, 2015, 06:40:50 am »

It doesn't do anything

325V 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 it

i'm lazy and i need dishwasher it calls for some bodging !

@mij59

sorry to disappoint you i just couldn't make it smoke this time, lots of fails on this one!

mij59 · « **Reply #17 on:** July 05, 2015, 07:15:33 am »

Quote from: DarkZero on July 05, 2015, 06:40:50 am

It doesn't do anything 325V 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 it i'm lazy and i need dishwasher it calls for some bodging !

@mij59

sorry to disappoint you i just couldn't make it smoke this time, lots of fails on this one!

That'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.

Psi · « **Reply #18 on:** July 05, 2015, 10:04:11 am »

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 years

their stuff used to be good

DarkZero · « **Reply #19 on:** July 05, 2015, 03:44:57 pm »

@mij59

voltage on source is 0v all sources are connected to 400v cap - pole

@Psi

Its actually bosch which imo is decently built but i doubt they make their own elektronic control

also 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

mij59 · « **Reply #20 on:** July 05, 2015, 05:05:16 pm »

Quote from: DarkZero on July 05, 2015, 03:44:57 pm

@mij59

voltage on source is 0v all sources are connected to 400v cap - pole

@Psi

Its actually bosch which imo is decently built but i doubt they make their own elektronic control

also 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

If 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.

DarkZero · « **Reply #21 on:** July 06, 2015, 09:47:18 am »

@mij59

yep tested all components i even checked with scope the damn thing just wont oscillate

anyway i appreciate your time big thanks ! althought i didn't fix original circuit i bodged it machine works but im not happy

its just a simple little circuit and i failed at that ... i ended up using 8v transformer with bridge rectifier.

mij59 · « **Reply #22 on:** July 06, 2015, 10:58:56 am »

Quote from: DarkZero on July 06, 2015, 09:47:18 am

@mij59

yep tested all components i even checked with scope the damn thing just wont oscillate

anyway i appreciate your time big thanks ! althought i didn't fix original circuit i bodged it machine works but im not happy its just a simple little circuit and i failed at that ... i ended up using 8v transformer with bridge rectifier.

Well at least you don't have to do the dishes, so success at last.

Probing with a ground referenced oscilloscope ?

Psi · « **Reply #23 on:** July 06, 2015, 11:31:49 am »

As far as im concerned a dishwasher PCB should be in a water tight container with IP rated connectors

Using 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.

DarkZero · « **Reply #24 on:** July 08, 2015, 09:15:59 pm »

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


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Author Topic: Trying to Repair Dishwasher Power Supply (Read 7310 times)

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