Electrical Another Thetford N3185 fridge problem

[jazzeddie1234]

So my replacement burner is working great which is a big relief but now I have an intermittent electrical issue - probably due to all the activity around the rear of the fridge.

Symptom: All lights flash after short drive on corrugations. Can only reset by unplugging the +12v permanent supply rail in the back. Otherwise fridge works just fine on gas /240/12 (when tug is not moving). I have wiggled /checked the supply cables - especially the 12 pin without triggering the fault. A read on UK websites suggest the front panel may be losing comms with the rear board so will check that next.

As an aside I found this really useful guide to enter service mode which I didn't know about. But the fault makes all the buttons unresponsive so I can't use that.

I learnt something useful from the guide anyway. I didn't realise the temp sensor in the fridge must be on a specific fin

 

[Boots in Action]

So my replacement burner is working great which is a big relief but now I have an intermittent electrical issue - probably due to all the activity around the rear of the fridge.

Symptom: All lights flash after short drive on corrugations. Can only reset by unplugging the +12v permanent supply rail in the back. Otherwise fridge works just fine on gas /240/12 (when tug is not moving). I have wiggled /checked the supply cables - especially the 12 pin without triggering the fault. A read on UK websites suggest the front panel may be losing comms with the rear board so will check that next.

As an aside I found this really useful guide to enter service mode which I didn't know about. But the fault makes all the buttons unresponsive so I can't use that.

I learnt something useful from the guide anyway. I didn't realise the temp sensor in the fridge must be on a specific fin

Hi @jazzeddie1234, as the problem occurs only after a short run on corrugated road and then causes an intermittent current to controls, which the electronics do not like, and so cause unit to go to "reset" mode. And the only way to get them going again is to disconnect active line, so electrics have steady continuous power again. This obviously resets the system again until next temporary loss of power. I would put my money on 12 pin plug being loose and vibrates loose on corrugations. Unlikely to be rear board as no problems unless moving over rough ground, but a bad solder joint always possible.

 

[jazzeddie1234]

That was my first suspicion except that the fridge electronics is powered from the van battery (a circuit I also wiggled) and I would have thought an intermittent 12pin feed would throw a fault code rather than all lights blinking. I have since wiggled all the power module connections with no repeat so I might check the feed from the setec to fridge and batteries to setec.
I might also try a short run over corrugations while on gas to eliminate/confirm the 12 pin

 

[mikerezny]

Hi,
my first guess would be that it does seem like an interruption to the 12V power to the fridge electronics.
If it was me, here are a few ideas that I might try that may help to track it down.

Have you got some 12V device that will flash if the power to it is interrupted. In the 240V world, it would be something like a telephone answering machine, digital alarm clock etc.
Whet I am thinking is, if you had something you could wire across the 12V supply to the fridge electronics that would give an indication that the power had been interrupted.
Failing that, you could try running a temporary wire all the way back from the 12V supply to the fridge electronics to a lamp in your front seat to monitor if it flashes while you are going over corrugations.

Failing that, in the van, wire a lamp across the 12V supply to the fridge electronics and set up a camera to record the lamp and the front panel of the fridge while you take the van over corrugations.

On another track, do you get the same symptom if you quickly toggle the power to the fridge electronics, say by pulling the fuse and plugging it back in or foggling the battery isolation switch?

take care
Mike

 

[mikerezny]

Hi,
there are quite a few threads on this forum relating to the N3185 and flashing errors.

Do a Google search on "thetford n3185 intermittent panel fault, all lights blinking" and you should get quite a few links to pages on expandasdownunder.

take care
Mike

 

[jazzeddie1234]

Some great suggestions - thanks. Yes a supply interruption is the most logical so monitoring the 12v van supply is an excellent idea. I have a 12v extractor with a clock so will see if it resets after a brief interruption because it's reading correctly at the moment.

 

[jazzeddie1234]

I decided to remove the fridge control board and found this

The 12v tug supply (earth) was badly overheated so cut the connector off and terminated in regular spade connectors until I figure out a permanent fix. The poor old low current earth was probably going flat out trying to handle the load...

 

[Boots in Action]

I decided to remove the fridge control board and found this
View attachment 67437
The 12v tug supply (earth) was badly overheated so cut the connector off and terminated in regular spade connectors until I figure out a permanent fix. The poor old low current earth was probably going flat out trying to handle the load...

Thought it might have been a "line in " problem that was not making a continuous connection for power supply. But then the earth return is part of the system.

 

[jazzeddie1234]

5kms of corrugations and no flashing lights!
Thanks all for you help

 

[Boots in Action]

5kms of corrugations and no flashing lights!
Thanks all for you help

So @jazzeddie1234 , we did not lead you too astray with our guess work. The simple faults are the hardest to find and we generally check them last!!!