Electronics Help - Dishwasher PCB

Toothy1911 · 25 Jul 2020 at 11:12

So my dishwasher decided to throw an error code and stop working. Turns out the solenoid for the heat exchanger was burnt out. Replaced with a new solenoid and that started to overheat too. I've stripped back to the PCB (power module) and identified a blown transistor.

I've ordered a new transistor (STN83003). Can anyone with a little more knowledge help out. Will I need to replace any inline components? Or is this likely to fix my issue.

brendy · 26 Jul 2020 at 01:41

Can't help an awful lot other than by saying try it, if it fails, I'd be looking at replacing the whole pcb.

norm · 26 Jul 2020 at 02:50

It's got to be safer replacing the whole unit. If it's burning out components do you really want to risk it catching fire.

https://www.esfrs.org/black-museum/all-the-black-museum-cases/faulty-dishwasher/

Jimbeam3678 · 26 Jul 2020 at 10:45

I was going to say the same thing, for the sake of what £200 for a new dishwasher?

Toothy1911 · 26 Jul 2020 at 14:16

It's a £600 Bosch that's only just out of warranty. PCBs are around £100 but no stock via Bosch at the moment, but I would consider that.
Totally hear what you're saying about fire risk. And it is duly noted. I will replace the transistor and test.

Funky-Melon · 26 Jul 2020 at 19:33

Unless you have a heat gun you may struggle to get that chip off. The pin on the 'drain' of that transistor will be coupled to quite a large pad on the PCB, lots of heat needed.

Best bet if you don't have a heat gun is a small bit of flux and and hold a fat tip (

) on it for a while to get the board hot enough to reflow.

Toothy1911 · 27 Jul 2020 at 07:49

Thanks. I only have a heat gun with a large nozzle, for paint stripping (and tube bending

) I guess I'd need one with a more focused nozzle. I might look at getting a cheap one, would be useful to have anyway.

Demon · 27 Jul 2020 at 14:13

A cheap 40W iron from screwfix would be fine..

It's personal but I'd give it a go, although I have all the correct tool so I'd be checking other components in the circuit after I'd removed it to check nothing is presenting a near short circuit..

Toothy1911 · 27 Jul 2020 at 17:15

I ordered one from Amazon. £23 delivered. I've got a pretty good iron already. Just needed the heat gun for the chips with multiple legs, will make it much easier to remove I'm sure. I can check individual components. But tracing stuff back through the board is where I run out of knowledge.

Toothy1911 · 30 Jul 2020 at 20:28

Transistor arrived. Was a little difficult to remove, but got it in the end. Mix of heat gun and soldering iron. Probably a no lead solder making it harder? Putting new one on was easy though. Just need to test it now. Bets on it blowing again??

Toothy1911 · 31 Jul 2020 at 16:09

Well. After all that. It didn't fix it. Still getting same error code. You think an expensive Bosch dishwasher would be better built than this.

Jimbeam3678 · 31 Jul 2020 at 17:04

Toothy1911 said:
Well. After all that. It didn't fix it. Still getting same error code. You think an expensive Bosch dishwasher would be better built than this.

Not if it’s the same internals as cheaper models with a Bosch sticker stuck on it. Surely a dishwasher is a dishwasher? Ovens etc are slightly different.

iraiguana · 31 Jul 2020 at 19:50

Either buzz out the rest of the circuit, to check for another failed component or wait for the BOSCH board look like your best options to keep this working.

ericmcn · 31 Jul 2020 at 20:48

i am an EE, with a masters and can replace all these components and fine footprints also, I just use the gear at work - firstly nice work on getting that replaced but unfortunately its not just a case of replacing parts - as you probably found out its something thats causing this failure in the first place, the root cause that you need to diagnose and without some skills and knowing what to look for its not so easy and takes time and indeed its probably easier to get the entire PCB replaced. Where else is the solenoid going to..? get a meter and buzz it out - its going to be tiresome so probably best to get a new main board

Toothy1911 · 1 Aug 2020 at 14:07

Thanks for the responses guys.
Only thing I can think now is I burnt out the new solenoid when it got very hot, before I found the broken transistor on the board.
The new solenoid does not get hot now ive repaired the board. But maybe because I broke it!

Any tips on diagnosing the solenoid? The original has infinite resistance measured across the two power pins. But the new one that got hot still shows some resistance, which I'd think it means its OK.

Somthing I'm a little unsure on is the power to the solenoid. Checking the connector plug, it seems to get a constant 240v. Even when the machine is off. Id expect it only to get a voltage when in operation.

ericmcn · 4 Aug 2020 at 22:27

I would be careful with messing around with stuff unless you know what you are doing, i honestly think the best way to go is replace the PCB - it will cost less than a dishwasher, google the PCB #. A solenoid can be driven from a MOSFET, ie the one you replaced - the MOSFET is driven from either a Micro controller or a gate driver depending on the current / timing / power requirements. Its no more complex than this, but unless you know whats going on...

The Solenoid once its switched on by a MOSFET or such the EMF field will be induced the the Solenoid will be in operation with a very large amount of current involved. Is there clamp diodes around the Solenoid? these can be used to reduce ripple or spikes - they could be dead, again you can check diodes with a DVM

Then Solenoid could be driven from a high or low side MOSFET (P / N channel) - P channel tend to be used for High Side switches, N channel are favoured for low side

edit** i see that transistor is a NPN - this is something that could drive a solenoid but i would just get a PCB tbh

5-electronic-circuit-schematic-controlling-each-of-the-solenoid.png

https://static-resources.imageservi...chematic-controlling-each-of-the-solenoid.png

Toothy1911 · 5 Aug 2020 at 07:01

Wow. Thanks for taking the time to respond with so much detail.
I've found a new board can be had for £100.
I'm going to ask someone at work if they can check the solenoid is OK. I'm hoping he says it's not, so I can try another new one.
Think I could return a new board if it doesn't work?

Redy322 · 19 Nov 2020 at 22:17

Toothy1911 said:
So my dishwasher decided to throw an error code and stop working. Turns out the solenoid for the heat exchanger was burnt out. Replaced with a new solenoid and that started to overheat too. I've stripped back to the PCB (power module) and identified a blown transistor.

I've ordered a new transistor (STN83003). Can anyone with a little more knowledge help out. Will I need to replace any inline components? Or is this likely to fix my issue.

I advise you to find a service on the Internet that prints boards, it will be cheaper than repairing. Of course first you need to make a circuit check to understand whether repairs are needed and maybe they will tell you the next steps as in my case. I'm sure because in my case it helped. I had a slightly different situation I decided to fix the board from my monitor and found this service. I gave it for diagnostics and they told what the problem was. My case was serious and it was easier and cheaper to order a printed circuit board, but you can save the situation if you understand what you need to do. It helped me personally, and I hope it helped you too. In any case, write later what happened.

Toothy1911 · 20 Nov 2020 at 00:29

Redy322 said:
I advise you to find a service on the Internet that prints boards, it will be cheaper than repairing

Thanks. But I've already fixed this about 3 months ago. I replaced the main board and it's been running great. Multiple components must have blown.

mattyg · 20 Nov 2020 at 01:38

ericmcn said:
i am an EE, with a masters and can replace all these components and fine footprints also, I just use the gear at work - firstly nice work on getting that replaced but unfortunately its not just a case of replacing parts - as you probably found out its something thats causing this failure in the first place, the root cause that you need to diagnose and without some skills and knowing what to look for its not so easy and takes time and indeed its probably easier to get the entire PCB replaced. Where else is the solenoid going to..? get a meter and buzz it out - its going to be tiresome so probably best to get a new main board

I use to own a Brown goods repair centre for Most major manufacturers. (largest in the NW) We used to have 14 x 4 drawer filing cabinets full of service manuals just for Tv's. It still irks me when people think they can "see" faulty components. Your eyes wont be able to tell you if a resistor is intermittent OC etc.

I had a neighbour bring his VCR round one day. (yeah that long ago) He said he had taken it into work and hooked it up to an oscilloscope but couldn't work out what was wrong...Well he wouldn't have. It was a stock Mech fault...

Good on the OP for having a go, But repairing down to component level is a little harder than looking