Chausson 12v fridge problem

[buddy]

If you do decide to check the power board fuse give all the multiplug terminals on it a good clean ,it is possible that a poor or corroded connection is the reason for a power drop after the point you found 14+ volts which could cause fault 6 to show.

[Derek Uzzell]

My Rapido has a Thetford N3150 SES (Smart Energy Selection) fridge/freezer that has similar operating principles to John’s N3142 model.

 

It may be stating the obvious, but for a SES appliance to operate at all it needs a 12V power supply. Consequently, as John’s N3142 functions from gas or 230V, it must be connected to a ‘live’ 12V supply. (Though, of course, that does not mean the 12V ‘cooling’ side of the fridge will work...)

 

When my N3150 is switched on and automatic energy selection is chosen by touching the “A” on the fridge’s control panel, the appliance will search for a gas, 230V or 12V power source and, if none of these is found, the appliance will go into fault state. Alternatively I can select a specific power source (gas, 230V or 12V) and if that source is not found an error symbol + number message will appear appropriate to that power source. So, if I select 12V as the power source and the motorhome’s engine is not running Error Code 6 will show up.

 

The attached image shows a Thetford ‘kit’ comprising the display + pcb, and (top left) the ‘Power Control Board’.

 

This MHFun discussion

 

https://www.motorhomefun.co.uk/forum/threads/thetford-fridge-freezer-n3000-series-problems.210369/

 

indicates that the Power Control Board is on the rear of the appliance.

[JohnPG]

Ok, so after a wet weekend last weekend with the rain coinciding with my available time, I have finally managed to get into the back of the fridge today.

 

Plenty of cursing and skin from knuckles later I managed to remove the power board in order to check the fuse. Ultimately that wasn't necessary. The burned out fuse was visible through the blackened board. If possible I'll load the photos. I'm surprised it's managed to blow and look so bad without causing more damage / still enable the fridge to work on 240v and gas.

 

For the sake of completeness I changed the fuse, just to check whether the blacked circuit board was only superficial damage only. It isn't.

 

Frustratingly I've put it all back together and in place before testing, so it's all to come out again to enable the installation of a new board.

 

Many thanks to all that responded to helped to diagnose the issue and provide the support to get my hands dirty.

[Brian Kirby]

What a silly place to hide a fuse! They are there to do a job, and if the blow they have to be replaced, which should not involve the need to replace the circuit board on which they have been mounted. Did you have any joy over the warranty validity?

 

One last thought. The fuse blew because excess current passed through it. I've no idea how a fuse in that position might have become overloaded, or whether the overload resulted from a different fault elsewhere on the circuit board, but if not, unless replacing the circuit board also removes the cause of the overload, there seems to me to be a residual risk that the same may reoccur with the new circuit board.

 

Having said which, I can't offer any help on how to check/verify the location of that fault. Sorry!

[JohnPG]

Hi Brian.

My sentiments exactly

1) Absolute madness to have a fuse which is so inaccessible.

 

2) The fact that the fuse has blown, should mean that the fuse is replaced, not the whole board, but the whole thing is blackened and a new 20v fuse hasn't made the fridge work - I have the same error message, so conclude the board needs to be replaced

 

3) I don't know how to stop the same happening again. Whatever has caused it to blow, could happen again. It seems new boards are £150 so it will be more than frustrating if it does blow immediately. If it did I'd then say the purpose of the fuse wasn't working. In fact, I should perhaps check that this should be a 20 fuse. It's possible an error was made and it should have been smaller.

 

Finally, yes I did check on the warranty position. A mobile service engineer told me that I wouldn't be covered, but that he wouldn't be able to do it due to being too busy.

 

Thanks for your thoughts and helpful comments.

 

Kr

John

 

 

 

 

[arthur49]

John

 

I have no connection with nor have I ever used this lot in the link, but if you're going to have to pay £150 for a new board might be worth checking with them if they can fix/upgrade/replace your current board?

 

I have heard good reports of their service though

 

http://www.apuljackengineering.co.uk/

[JohnPG]

Just for confirmation, it is a 20amp fuse.

[buddy]

It is possible that the fuse had a poor connection in its holder to cause it to over heat but it would also be worth checking the heater resistance ohms, in case they are incorrect and caused the problem before fitting the replacement/repaired board.

[Brian Kirby]

JohnPG - 2021-05-23 4:38 PM................................3) I don't know how to stop the same happening again. Whatever has caused it to blow, could happen again. It seems new boards are £150 so it will be more than frustrating if it does blow immediately. If it did I'd then say the purpose of the fuse wasn't working. In fact, I should perhaps check that this should be a 20 fuse. It's possible an error was made and it should have been smaller.

Finally, yes I did check on the warranty position. A mobile service engineer told me that I wouldn't be covered, but that he wouldn't be able to do it due to being too busy.

Thanks for your thoughts and helpful comments.

Kr John

I'm unfamiliar with the insides of fridges, so can't begin to guess what the 20A fuse is intended to protect, except possibly the power supply to the fridge 12V heating element. As fuses are there to protect the wiring (i.e. it is the wiring that would overheat and possibly cause fire in the event of overload) a fuse rating is selected that ensures the fuse blows before the wiring gets seriously hot.

 

This is on the understanding (mine! 8-)) that most of the current flowing around printed circuit boards is low, which is why a 20A fuse on a PCB surprised me. But, there are wires of apparently fairly heavy gauge seemingly attached to the board in the vicinity of the fried fuse carrier, which suggest they might be feeding something with a relatively heavy current demand. 20A x 12V=240W, which is quite chunky, but would have to be comfortably above the Wattage of the 12V heater element to ensure everything runs cool in normal circumstances. I see that some of the Thetford 12V elements are being quoted on-line at 190W, so a 20A fuse seems appropriate. In which case I wonder if your 12V element has failed, and in the process shorted, which would easily blow a 20A fuse.

 

So, I think it may be worth testing resistance of the 12V heating element. If it has failed, it should show a pretty much infinite resistance between the feed and the return wires. However, I think I'd also test resistance between the feed and the element jacket to see if the short is still present. It may be simpler than that, because once you get to the 12V element it may be obvious that it has failed, or it may possibly be that one of the wires has detached from the element and shorted onto the fridge metalwork, though the pictures of the elements suggest that is relatively unlikely.

 

To me (as above, no expert!) that presently seems the most feasible explanation for the blown 20A fuse. That the blown fuse fried half the PCB just seems to me bad design - though I'm sure Thetford would say it is extremely rare for the 12V element to fail.

 

Silly comment, I'm sure, but do make sure the 230V power is detached from the van when exploring for the 12V element, as I suspect both elements are close together. Safety first!! ;-)

[Alanb]

John,

 

Many thanks for keeping the forum informed.

 

From the evidence of your photographs, there is a possibility that the initial cause of the problem may have been high contact resistance, between the fuse holder and the fuse. If the fuse became overheated due to this, it could conceivably fail under near normal load current.

 

As a precaution, it may be worth trying to measure the fridge 12V element resistance. This will be in the region of 1 Ohm. A more precise value may be obtained by reading the 12V watts for your fridge from the fridge label, and dividing this into 12V squared. That is 12 x12 / watts = resistance in Ohms. When trying to measure relatively low resistances with a multimeter, the resistance of the test leads is significant. So measure the leads shorted together, and subtract this value from the total reading.

 

The only reason that I can suggest for the on-board fuse, is to ensure a correct fuse rating, when the supplying fuse in the 12V distribution board may be rated at up to 30A. In this context I suggest checking condition of the fridge fuse in the CBE DS300xx 12V distrbution board, which is located in the Technibox. The fridge fuse should have a snowflake icon.

 

My suggestion for a possible repair would be to remove the fuse holder from the control pcb, scrape off any carbonaceous deposits, and solder a wire bridge from the HC12V terminal to the point in the circuit supplied by the fuse. This point could be a relay controlling the 12V element. If this approach is adopted then ensure that the fridge fuse in the CBE unit is not greater than 20A.

 

For what could be a bit of solace, see this thread. You are not alone.

 

Alan

[Robinhood]

Brian Kirby - 2021-05-23 6:33 PM

 

I'm unfamiliar with the insides of fridges, so can't begin to guess what the 20A fuse is intended to protect, except possibly the power supply to the fridge 12V heating element.

I think from the PCB markings it is absolutely the 12V heater circuit.

 

(From my limited knowledge of repairing a friend's Dometic similar, it seems to me that Dometic, at least, have decided to keep the 12V heater circuit and its larger wires, well away from the PCB).

 

Anyway, more relevantly, the OP may want to peruse this thread:

 

https://www.wohnmobilforum.de/w-t132344.html (using translation in whatever browser)

 

...where there is length discussion of exactly the same issue on the same PCB.

[JohnPG]

All, very many thanks for follow up comments. I'm going to need to reread some of these to fully understand the implications, but all comments are very much appreciated.

 

Robinhood - fab. That link could be my board!

 

Although burned out, I've just tested the fuse, and the multimeter reading shows that the fuse is actually ok. i.e. the plastic outercase is burned to a crisp, but it has not melted through.

 

I'm now around to concluding that this was not the 20amp fuse issue, but is a load issue onto the board. I'm not au fait with direct soldering points, so there's some bedtime reading.

 

Ultimately, the cause needs to be addressed and remedied, before I start with either a new or repaired board being installed. At this point, it might be a 12v heating element, or simply it not being able to withstand continuous 12v supply on long journeys. Neither of which are ideal.

 

Thanks

 

John

[Brian Kirby]

JohnPG - 2021-05-24 10:54 AM

All, very many thanks for follow up comments. I'm going to need to reread some of these to fully understand the implications, but all comments are very much appreciated.

Robinhood - fab. That link could be my board!

Although burned out, I've just tested the fuse, and the multimeter reading shows that the fuse is actually ok. i.e. the plastic outercase is burned to a crisp, but it has not melted through.

I'm now around to concluding that this was not the 20amp fuse issue, but is a load issue onto the board. I'm not au fait with direct soldering points, so there's some bedtime reading.

Ultimately, the cause needs to be addressed and remedied, before I start with either a new or repaired board being installed. At this point, it might be a 12v heating element, or simply it not being able to withstand continuous 12v supply on long journeys. Neither of which are ideal.

Thanks

John

Which, IMO, points to Alan's post just above (23 May 2021 8:26 PM), suggesting that the fuse holder itself is a more probable culprit.

 

If the 12V element tests clean then, unless there is some other unidentified cause within the PCB, it seems that when running on 12V there was some arcing between the holder contacts and the fuse blades, presumably due to loose fit of the fuse, which would, inevitably, over time, build up, possibly distorting the fuse holder to increase the gap and the arcing, plus the resulting heat, until either the holder post contact with the PCB, or the fuse blades lost contact with the holder. Result: no 12 power to 12V element!

 

From your photo the PCB looks quite extensively distorted, and possibly somewhat delaminated, in the vicinity of the fuse holder, so it seems you're stuck with a new board whatever the cause. At least, I don't think I'd want to trust that board even if repaired! After all, the heat may have damaged other items on the board. Unless the fridge was removed in the past for other reasons, and the fuse or holder knocked in the process, it appears this fault must have been present from day 1, and slowly worsened until the 12V supply failed altogether.

[Brian Kirby]

PS, but I should have added above to do as Alan also suggested and check the 30A fridge fuse on the main CBE DS 300 fuse board, as it is possible (though I think unlikely in view of the fuse rating) that it blew before the fuse on the fridge PCB, which might have left the fuse on the PCB very hot but intact. If that proves the case I think it would leave us back at failure of the 12V heating element as probable cause.

[JohnPG]

Hello Brian,

 

Thanks for your contributions. I've been to check the main CBE fuse board again, just in case I had missed the blown fridge fuse. The fridge 30a fuse is intact there- as you suspected.

 

I'll try to test the 12v heater at the weekend.

 

I've been mulling over how hot that board must have been and the fire risk. Perhaps I'm being dramatic, but if the gas had been left on whilst travelling the risk must exist of a greater danger. Given that it seems that I'm not the only one with this issue, and if Dometic have now moved their 12v heater circuit away, it begs the question if Thetford should.

 

Warranty or not, I'm now in touch with a Thetford Service centre who I want to have a look at it.

 

I'll keep the thread updated with news when I have it.

Kr

 

John

[Brian Kirby]

'Morning John.

 

Bearing in mind the difficulties over the past 14 months caused by Covid, plus those in initially discovering a) that the 12V heating circuit had failed, b) that a critical fuse is mounted in a position only accessible with the fridge removed, c) that the fuse holder was defective and did not make proper contact with the fuse (resulting in severe overheating of the holder sufficient to damage both fuse holder and PCB to the extent that both have to be replaced) and d) that neither the Thetford fuse nor the supply fuse on the CBE fuse panel had blown (so there is no other logical cause of the PCB damage), I think Thetford owe you at least a replacement PCB FoC under warranty. The more so when it appears from robinhood's (well done Bob!) German link that sloppy fit of their fuses leading to PCB damage is a problem already known to Thetford.

 

With all that in mind, that the fridge is now a matter of weeks outside its warranty period should not prevent Thetford from exceptionally honouring the spirit of their warranty. After all, the origin of the fault is, apparently, a defective component supplied and fitted by Thetford that no-one else can reasonably be supposed to have tampered with.

 

The fridge automatically seeks it energy source, and will only select the 12V source until the engine is started - at which point both driver and passengers must reasonably be supposed to be seated and belted and so unable to see the fridge control panel on which any failure warning might appear.

 

If then, as appears the case, when the engine is stopped the fridge then automatically switches to gas - or if available 230V power - it cancels any fault messages in the process, the owner can hardly be penalised for remaining unaware of the 12V power failure.

 

Under those circumstances, I think a reasonable company would make an exception and take responsibility of a fault that was of its own making that, under present circumstances, a user could not reasonably have been expected to have become aware of.

 

I'm saying all this in the knowledge that under the terms of their warranty Thetford are sole judge and jury over its interpretation, that the concept of reasonableness has no part in that interpretation as it undoubtedly would in a court of law, and that you have no legal recourse to Thetford under consumer legislation as you have no contractual relationship with them. But there should nevertheless be a route for you to escalate a late warranty claim within their organisation. Perhaps the Thetford Service Centre could be persuaded to press a claim on your behalf when they have seen the evidence plus that fried, but intact, 20A fuse, (so don't bin that!).

[Robinhood]

JohnPG - 2021-05-25 9:27 PM

....and if Dometic have now moved their 12v heater circuit away, it begs the question if Thetford should.

 

John

...I can't vouch for the design of all Dometic fridges, but on the one I diagnosed for a friend (which had a failed 12v operated relay in the 230v supply, which we managed to get replaced on the existing PCB for about a tenner), for 12v use the low-current control voltage went via the PCB (for the switching logic), but supplied a (automotive-type) 12v/12v relay mounted on the rear of the fridge, the higher current heater circuit and wires that it controlled going nowhere near the PCB.

[JohnPG]

Hi Robinhood,

 

Sorry, you're quite right.

I don't know whether Dometic have kept the higher voltage away because of this issue, a different issue or possibly do have a similar set up on other boards (and that wasn't inferred in your post).

 

I think I'm still just a little sore on the matter.

 

Thanks

John

 

[JohnPG]

Further update.

 

Credit to Thetford.

 

They have been back in touch to confirm that they are aware of an issue on some N3141/N3142 boards and that there is a modified pcb board available to alleviate the problem.

 

They have offered to cover the replacement under warranty, and the cost of the labour associated with it. I couldn't ask or expect anything better than that.

 

Thanks for everyone's contributions and suggestions- it's been a pleasurable first contribution on the forum.

 

Thanks and kind regards

 

John

[flyboymike]

If it is any consolation I am having exactly thr same problem with N3142 fridge in my 2018 Dethleffs. It came up code 6 on the diagnostic. 12v element checked out as closed circuit, control board with overheated terminals in the same place as your picture above.

Think there is a problem with the design/manufacture of the board 691101. Ordered replacement now has a new number 692247 so hope Thetford have solved the problem.

[Brian Kirby]

JohnPG - 2021-05-28 11:56 AM

Further update.

Credit to Thetford.

They have been back in touch to confirm that they are aware of an issue on some N3141/N3142 boards and that there is a modified pcb board available to alleviate the problem.

They have offered to cover the replacement under warranty, and the cost of the labour associated with it. I couldn't ask or expect anything better than that.

Thanks for everyone's contributions and suggestions- it's been a pleasurable first contribution on the forum.

Thanks and kind regards

John

Excellent news. Well done!

[flyboymike]

I emailed Thetford with my concern that the 20 amp fuse and fuseholder were not up to the job and this is part of the reply:

 

This (along with part standardisation) is one of the reasons why the original PCB was replaced by 692247. The original was fine when supplied with 12V, but modern vehicles, especially those equipped with smart charge and stop/start systems can have a relatively high alternator voltage which pushes the element current draw over the limit of the PCB which can cause the overheating you've discovered. The new PCB has heavier traces for the 12V element, along with a 25A fuse to eradicate this potential issue.

 

So as I now have the new module installed I shall see how it performs. Thetford have also changed the 240AC to a pulse width modulation system to control the supply fluctuations experienced across Europe with mains electricity.