Bosch dishwasher woes - chasing repair manual

[gizmo]

 

A few weeks ago I looked at a Bosch DW for a friend, that one was completely dead and had an obvious blown up chip on the main board, the board was $388 so the machine was replaced with a new F&P dishwasher. I have the dead one in my shed.

Now another friend has asked me to look at their Bosch dishwasher, a similar model but a few less features. Both approx 10 years old. The second one is a Bosch SMU50E15AU. I assume the AU on the end just means Australian market. This one tries to work, it does an initial pump out, then at fill stage it doesn't fill. It is NOT the fill solenoid, I have checked that and it is OK. I believe it is a main board fault again. This board is $420 but I have the other machine's board to pinch components from, it is almost identical but not quite. I'd like to try to get this one working by swapping components from the other board, but I can't find any obviously faulty components. It is mostly SMD devices so this will test my soldering ability.

 

First up, I'd really like a repair manual for this SMU50E15 dishwasher, can't find one online. Does anyone have a link to a suitable manual for this model or something similar? 10 years old, Bosch, made in Germany.

 

So far... the solenoid is 240 V AC and there are tracks on the board for both Active and Neutral 240VAC, not through the switchmode power supply. These appear to be all OK - I can measure continuity to the switching triacs for all the solenoids, which are on the neutral side. The Active side - feed to the solenoids leaves the main board, goes to the flood float switch in the base, then back to the board, then out to the solenoid, the solenoid neutral is switched by a triac. All this circuit tests OK from AC Line in (Active) through float switch, solenoid to the triac. So it appears either the triac is faulty (not switching on) or not being switched - the microprocessor switches it through a transistor and a couple of resistors. The transistor may also be faulty, the resistors test OK. There are several identical circuits, one for each solenoid, and they all check out the same when I check the components resistance from terminal to terminal with a multimeter. So unless I'm missing something, either a transistor or triac (that physically looks OK and tests the same as its neighbours with simple resistance tests terminal to terminal) is faulty, or the microprocessor is kaput.

The other possibility is some sensor is detecting a fault and so the processsor is not commanding a fill - but that appears unlikely, as the machine sits and waits for a fill, then appears to time out and goes to "end" and displays a "check water" light. It doesn't have any useful display, just an "active" LED during operation, plus LEDs for End, Check Water and Rinse Aid.

I've tried manually filling it with a bucket - it washes for a few seconds, then stops and pumps out. It is a 3 phase combined pump with inbuilt single phase heater, pump turns a few seconds,  heater tests OK but never turns on. I have a spare from the first machine, they are the same. I haven't tried fitting the spare pump yet - there are 3 sets of connections to the pump/heater unit:  for pump motor - 3 purple wires; for heater - 2 heavy red wires; and for something else, maybe temp sensor or tacho? - 3 grey wires. Could a fault in the 3 grey wires cause this fault? Any other suggestions?

 

The First machine, the dead one, after I said I couldn't fix it, the owners phoned around to get someone else to look at it. Every repairer they tried said pretty much the same- they wouldn't even look at a Bosch. Just throw it away. Online reviews of the later one, that I'm still trying to resurrect, are poor, with many reports of "check water fault, it was the main board at a cost of over $400." So I suspect I'm wasting time on this but if swapping over a triac or transistor can fix it, I could do that. It some sensor is stopping the processor from trying to fill, I probably have a spare on the other machine.

 

OK folks, what can you add? Anyone have a link to a service manual for this machine or something similar?

 

Oh, it's awful to work on, too. So cramped underneath, you have to lift off the whole wash compartment to get at the pump for example. Eeek.

 

[gizmo]

oh, and...

...something weird I noticed.

In tracing out the wires to and from the flood float switch - it is a changeover switch with NC and NO contacts. There are 3 wires, so both the NC and NO contacts are used. The NC contact supplies 240V AC back to the board, where it is then fed to the solenoid valve in question and must also be detected by the processor.  The NO contact goes to another contact on the main board that is also live any way - so of the 3 wires from main board to the float switch, one is switched, the other TWO are always live, fed 240VAC from the main board. I can't see any reason for the two redundant wires to the float switch, one to Common and the other to NO on the switch, both always live at the main board end. I would have thought this indicated a fault on the main board, but the other board test the same... WTF? However, the other board is known faulty, so it may be that they both have the same fault. Or maybe the NO contact isn't ALWAYS live? This in particular is where a circuit diagram would help. Main board is 9000588642, also labelled 9000 597 461 and 5560 D001000794 B.

Thanks.

Help?

 

[rolls_rapide]

Before you do anything else, have you checked the 'flow-through sensor'? This meters the water entering the machine. Apparently they do go wrong, magnetic Hall-sensor or some such.

According to the exploded diagrams, it is a component (replaceable), within the water matrix heat exchanger.

https://www.bosch-home.com/ae/suppo...21#/Tabs=section-spareparts/Togglebox=tb0405/

Diagram 4/6, item 0405.

 

[ozzie908]

@gizmo

The 3 wires on your float switch are if I recall correctly 1 feed to the fill valve and the other feed to the pump when the switch is triggered so it should cut the power to one while powering the other.

Austin

 

[gizmo]

It's fixed.

Thanks Rolls and Austin for your help.

I checked the flow sensor. It was OK.

The 3rd wire goes to a relay, it probably has something to do with the drain pump as you mentioned, but this machine has a tiny 3 phase motor for the drain pump, so it is driven through a motor controller circuit, not directly from AC 230V so it isn't driven directly by the float switch third wire. (it might be triggered by it??)

 

Any way, I ran it again and found I had previously missed something it did when starting a cycle. It would pump out briefly to empty any old water in the sump, then it would run the wash pump for about 5 seconds, then stop.  Then it would sit a while, operate the drain pump a few times, then end and display the "check water" light. The key thing I had missed was that few seconds of running the wash pump. (The drain pump and wash pump sound very similar in this machine - they are both small 3-phase motors.)

I watched a youtube last night about how to test and replace a wash pump/heater unit for this machine - the wash pump and heater are all in one unit. I tested all the terminals on the wash pump / heater assembly - 3 motor wires, 2 heater wires, 3 temp sensor wires and an earth (ground) wire.

Everything tested perfectly to spec. However, I had a spare of the same unit in the dead dishwasher from a few weeks back.

The pump/heater assembly is a cow to get at, I wasn't keen to swap it just to test, so I just disconnected the wire plugs from the original unit, pulled them out the side of the dishwasher, and plugged them in to the spare. Power on, press start... It ran the drain pump briefly as normal, then ran the wash pump, this time it kept running, then emptied the heat exchanger into the dishwasher, then took in water from the inlet hose, and kept washing!

Success!

In case I had just jiggled a bad connection, I put the wires back to the old pump/heater and tried again - the fault was back.

Next I shut the machine down, disconnected from power, moved the main board out of the way, removed the wires from the pump/heater, removed the rubber mount and yanked out the pump as shown on the youtube.

 

I wanted to see what was wrong with the faulty one. I checked everything with a multimeter and compared to the good unit - they were the same! No shorts in motor windings, no shorts to earth, sensor tested to spec. Hmmm.

 

I pulled the unit apart (it is designed to go together once, disassembly is made difficult by 4 strong barbs) and found the bearings in the motor, fully submerged bearings that look like ceramic(?), were worn to an obvious oval hole and the rotor was able to touch the side of the bore and this drag would have been detected as excessive current, causing the shut down. So the pump is just worn out.

The spare seems a bit sloppy too but it works fine for now.

 

Despite this being a motor fault, the dishwasher displayed the "check water" light, which was a red herring.

2 dead dishwashers turned into one working dishwasher and a stack of spares. A good day!

 

 

[rolls_rapide]

At least you got it sussed.

It's a pity Bosch had the daftness to create a flimsy wash pump - with the heater in the same unit. Obviously the accountants had control of that design.

 

[DADoES]

 
Flow-through water heating is touted as a premium feature on brands/models that have it.

 

[henene4]

Flow-through-heaters

Don't have to be bad.
Bosch and Miele had them on their machines for decades with rarely any issue.

Miele dosen't appear to have issues with heating elements on their current and last generation.
Only the BOL machines of th G4xxx machines that had the single speed pump had some premature failures.

The current BSH design is luckily pretty easy to replace and relativley cheap.
Some people seem to have issues with them way more though then others.
Though heater failures are way more common then pump failures in my experience.

My current best guess is it's up to detergent.

These have 2kW of heating power on a small area. Thus they rely on good heat transfer.
So either very hard water with to little detergent or just no good detergent could cause scale residues.

On the other hand, very suds detergents can cause the pump to cavitate more (or to better say, pull to much air together with the water).
That could cause hot spots on the heater.

 

[rolls_rapide]

Flow-through heaters

Ah, but isn't the Miele flow-through heater more like a conventional immersion type heater, looped within the wash pump?

The Bosch heater seems to be more of a 'printed onto steel tube' design. In fact it reminds me of the 'Blake's 7' teleporter bracelets.

 

[henene4]

Both Bosch and Miele used to have a typical heater in a casing like you described.
Bosch's was quite literally their washer heaters placed in a housing between pump and water diverter.
Miele had a long heater in the tube to the middle rack sprayer, thus only heated while running the middle rack (if I am not mistaken at least).

At least with the G7000 and I think even with the G6000 series they have a similar heater to BSH now has.
I actually think all Miele machines with variable speed pumps have that kind of heater... but unsure.
The one deviation from that I think are the semi-commercial machines with the higher heating power. They have the same pump format with an adapted motor but the same mount and heater plus a typical coil heater. If connected to single phase they only use the heater integrated in the pump, if connected for higher wattage operation both heaters are connected.

The 3 reasons I know for that change are that they are cheaper, they allow for lower fill volumes and better heat transfer.

 

[henene4]

Bosch heater

So at least the G4000 did have a heater coil that could be replaced seperartly.

One thing that kind of annoys me is that you can easily split the heater and pump on the BSH design, but can't buy the heater on its own.
So wasteful for no reason.

 

[jerrod_six]

The first month I had my 6987 series Miele Dw it had three circulation pump faults so the pump was replaced. I kept the pump to look it over and found that only one of the three water supply outlets was open(probably to the middle wash arm since it always starts spraying first). Looking inside the outlet you can see a metal rod. I don't know for sure but this might be the heater. The pump is variable speed.

 

[ozzie908]

@Jerrod

That is the heater you can usually tell by the connectors that are separate to the motor ones..

Austin

 

[ozzie908]

@gizmo

Could it be such a small clearance that the rotor shorted out on the stator ? It may not know what to call that fault but as it would have done it when it does its system check maybe that was the only thing it come up with?

Anyways sorry to have not been much help but how brilliant that you got it to work so you now have a spare DW

Austin

 

[rolls_rapide]

Reply #11

Yes, I do believe that is the heater element. It loops almost full circle, the shank with the spade connector protrudes through the pump fascia, at right angles to the loop of the heater.

 

[gizmo]

Hi Ozzie

Not really shorted out - both the inner cavity and the rotor in it are fully encased in plastic.  So it was plastic-on-plastic friction. There are deep grooves where they have been rubbing. I suspect it was detecting overload, not shorting. The old one used about 40 Watts running empty, the new one was more like 10 or 12 Watts. The dishwasher has no numerical display, the only fault lights are "check water" or "rinse aid" so I guess it was check water or nothing. It may have been flashing a code too - I didn't think to count the flashes.

The dishwasher is going back to its owner. I actually don't have a dishwasher. Just a pile of spares

.

Chris.

 

[ozzie908]

@gizmo

Whaaaaaat no dishwasher? Thats awful how on earth do you cope? lol Personally I would rather have no washing machine than dishwasher as I detest washing up big time and will go any length to avoid it...

Maybe when you find another Bosch you can fix it with some of the spares you have ?

Austin

 

[gizmo]

Hi Austin

Maybe, but TBH I don't really want a dishwasher.

All my cookwear is in excellent condition, everyone I know with a dishwasher has degraded saucepan handles, permanent dirty marks that don't go away (till I handwash the item...), etched glassware, and so on. (Which may well be operator error, I admit.) I'm not a collector, but I have a bit of a thing for Lustreware and it is not dishwasher safe.

 

When we built this house I allocated a spot for a future dishwasher in the kitchen layout, but I put 2 extra pot drawers in the space and would not want to lose them now.

 

I'm the cook in the house, the deal with my partner is, if I cook your dinner, you do the dishes. Works for me...

(He's happy about it, too.)

 

We are about to build a new shed up the hill, mainly as a workshop for me, I might fit a dishwasher in there for very occasional use - mainly for rangehood filters and cleaning off oily mechanical spare parts. More of a parts washer in practice, but it would be a domestic dishwasher. It will be 5 minutes walk up the hill from our house, so it won't get household dishes.

 

Gosh they are rotten things to work on compared to washing machines, too...

Chris.

 

[rolls_rapide]

"Gosh they are rotten things to work on compared to washing machines, too..."

I think you're quite right, regarding the modern machines. Tho older machines were easier to access (access from underneath). With the new ones, it's more of a complete strip down.