Dometic RM7401L - no power

[melon]

My fridge has no power, nothing lights up on the control panel.

Was working fine on 240v and gas.
I'm in the midst of adding a battery and doing some rewiring - I moved the 12vDC input (red/white, not the violet/black ignition) over from what I assume was trailer plug wiring to a terminal on my battery fuse block. I think it may have fired up for a second when I turned the fridge switch over to 12v to test (can't be 100% sure, but I think I remember seeing a spike on my battery shunt monitor), then everything just died. Nothing lights up on the control panel at all now.

I've tested the fuse on the back of the control board, it's fine.

This thread brought me here when going down the google rabbit hole - https://www.rvnetwork.com/topic/122661-dometic-fridge-has-no-power/page/4/ - and while it's got lots of great info, I'm just wondering if anyone could help with some more specific troubleshooting or point me to a service manual (can only find user manuals for my model)?

I'm a novice with a multimetre, but I can see that there is power getting up to the control board -

If I hold the red thingy from the multimetre to the point on the orange arrow in the pic below, then turn the dial to ignition, then the LED lights up (but no clicking sound of ignition). If I move the dial down to 12v then that LED lights up as well.

Really appreciate any help here, I've gone just about loopy getting to this point!

[Kirk W]

This Schematic is all that I found other than operating and installation instructions for that refrigerator. The one that you have is not sold in the USA so I have never seen one like it. 

6 hours ago, melon said:

I'm in the midst of adding a battery and doing some rewiring - I moved the 12vDC input (red/white, not the violet/black ignition) over from what I assume was trailer plug wiring to a terminal on my battery fuse block.

I made my career repairing electrical equipment and it has been my experience that when something stops working after a modification to the wiring has been made the problem is usually related to the changes made. Have you tired returning the wiring to what it was before you started?

[melon]

51 minutes ago, Kirk W said:

Have you tired returning the wiring to what it was before you started?

Yeah that's very perceptive, very good advice.

I moved the violet/black gas ignition wiring to the battery first (before moving red/white over), and had that running for a day or so with no issues. The issue only started when I moved red/white over to battery as well.
I have since moved red/white back to orig, leaving v/b on battery, but have not returned to what was a working situation.

My next step is to move v/b wiring back over to orig as well, but I do doubt that this is the problem unfortunately.

Edited January 5 by melon

[Wrknrvr]

 I would suggest to put everything back to where it was. Even eliminate they extra battery.

   See if things work as before. If not trace where the problem is.

 

   We need a baseline starting point. That is working.

[melon]

OK he's all hooked back up to the original wiring method, and I'm still getting the same symptoms.

No lights at all on the control panel 😢

[Kirk W]

Now you need to get your multimeter and see where the voltages are available and where they are not, based on the schematic. Once you know where the voltage is lost, turn off all of the eclectic supplies and then use the ohmmeter side to determine where it is being lost. 

[melon]

I'm struggling with this a bit sorry

I've checked all the points on the circuit board where the wires come in, and most of them are displaying active voltage.

Are there any specific points where I should be testing?

And how will my multimeter display anything (ohms?) if I turn off all of the electric supplies to the fridge?

[Kirk W]

5 hours ago, melon said:

Are there any specific points where I should be testing?

Look at the schematic from the link above to see what should be available and what it should read. I don't know what you mean by "active voltages" but you need to see what it is. The 12V is direct current. 

The power from the mains will be 240V or close to that.

5 hours ago, melon said:

And how will my multimeter display anything (ohms?) if I turn off all of the electric supplies to the fridge?

You need to learn how to use your meter for the information to have any value to you are us. It should have several voltage scales for alternating current, several more for direct current, and several for ohms. You select the appropriate one for what you are checking. Based on what you have said, I think that you need to get some qualified help.

Edited January 8 by Kirk W

[melon]

I would really love some qualified help, but unfortunately I just can't afford it. That's why I'm trying my damnest to figure out what component might be shot so that I might have the chance of replacing a small component rather than having no fridge all summer. I do apologise for my lack of knowledge, but am nothing if not persistent and with some kind and generous help I'm sure I can at least save myself paying a diagnostic fee just to be told that the whole thing is wrecked and should be put in the bin.

Unfortunately I don't have a proper multimeter, just a little device that tests for the DC - it displays either low (under 5) medium (5-10) or high (12). When I said active current, i just mean that I got live readings from all of the points I tested on the circuit board. I can't remember if they were all 12 or not. Would a reading under 12 indicate an issue with that particular point?

[Jaydrvr]

48 minutes ago, melon said:

I would really love some qualified help, but unfortunately I just can't afford it. That's why I'm trying my damnest to figure out what component might be shot so that I might have the chance of replacing a small component rather than having no fridge all summer. I do apologise for my lack of knowledge, but am nothing if not persistent and with some kind and generous help I'm sure I can at least save myself paying a diagnostic fee just to be told that the whole thing is wrecked and should be put in the bin.

Unfortunately I don't have a proper multimeter, just a little device that tests for the DC - it displays either low (under 5) medium (5-10) or high (12). When I said active current, i just mean that I got live readings from all of the points I tested on the circuit board. I can't remember if they were all 12 or not. Would a reading under 12 indicate an issue with that particular point?

There are dozens of inexpensive but functional meters available online that will work well. Here's just one. You need accurate readings to tell what's going on. Jay

AstroAI Multimeter Tester 2000 Counts Digital Multimeter with DC AC Voltmeter and Ohm Volt Amp Meter ; Measures Voltage, Current, Resistance; Tests Live Wire, Continuity https://a.co/d/53watmo

 

[Kirk W]

On 1/5/2024 at 12:11 AM, melon said:

I've tested the fuse on the back of the control board, it's fine.

How did you test the fuse? The only way to be absolutely sure is to check it for continuity with an ohm meter. If you didn't do that, at least replace the current one with a new one of the same ratings. 

3 hours ago, melon said:

Would a reading under 12 indicate an issue with that particular point?

The first thing that you need to understand is that the voltage from your battery is not always 12V, even under normal conditions with a good battery. A fully charged battery will supply as much as 12.6V when fully charged and can be as high as 13.6V if recently charged. As the battery is depleted it is normal for the voltage to slowly fall. Most RV appliances will operate down to 10.5-11V supply. If you measure between the + and the - on the schematic you do need to have at least 10,5V. Other points on the circuit board could be quite different depending on where you are reading in the circuit. Just what you should find at any point depends on where in the circuit that point is. 

Anything supplied by the mains supply should be at or near 240V but that voltage is alternating current and probably would damage the device that you are using. 

I strongly advise you to at the least, get a cheap multimeter and learn to use it from the instructions that will come with it because there is simply no way of knowing what is wrong with the refrigerator that you have without one. If you are rewiring things in the RV without the use of a reasonably good meter and a basic knowledge of electricity and RV electric systems, I am not surprised that things are not going well. People are not often seriously hurt by 12V systems but it does happen and the 240V mains is very dangerous. The problem with your refrigerator might be something as simple as a bad fuse or a poor connection, but it is also possible that the circuit board or other electrical components have been damaged or destroyed. If you plan to continue to work on the RV and refrigerator, you should take the time to read "The 12V Side of Life" parts 1 and 2. Doing so will not make you an electrician but it will give you some basic knowledge of how things work. 

[melon]

Thanks for your help so far!

I've borrowed a multimeter, and tested the fuse that's located directly on the circuitboard I posted in the OP. It's measuring 1.6 ohms, and google tells me this is good.

The fridge is not using a battery at all now, as per the earlier instructions to take the wiring back to what it was originally.

There is a 'battery eliminator' 12v power supply that's plugged in to shore power, this is where the fridge gets its 12v for the ignition circuit from.

There is currently no 12v power input (van is not connected to a car, which is where this is wired to), and the 240v plug is unplugged for safety while the circuit board is exposed.

Now I'm taking another look at the schematic to see where I should be poking this thing to get some useful readings 🤓
 

Edited January 9 by melon

[Wrknrvr]

    If I was there on a service call, I would replace the fuse with a new one.

 

   A few weeks ago I had a low amp fuse that tested good and past voltage. But would not pass amperage.

   That’s confusing isn’t it.

  Put a new fuse in and the Schwintec slides worked. After sometime spent checking the system for the normal things.

 

    Also I see the battery is not connected. That could be a problem. I have seen that cause odd problems at times in control devices.??? 

[melon]

22 minutes ago, Wrknrvr said:

    If I was there on a service call, I would replace the fuse with a new one.

 

OK sure, I will do this and report back.

22 minutes ago, Wrknrvr said:

    Also I see the battery is not connected. That could be a problem. I have seen that cause odd problems at times in control devices.??? 

 

The 12v ignition is wired to a 'battery eliminator' 12v power supply, that's connected to 240v shore power. With 12v supplied to the ignition wires (even if it's not also supplied to other 12v power circuit in the fridge), the control panel would (previously, before all this unpleasantness) light up fine and let me run via either gas or 240v. The other 12v power circuit is wired to the trailer plug - so currently has no power as the van is not hooked up to my car at the moment.

Current situation is, even with 12v being supplied to the ignition circuit (tested both via battery eliminator, and a newly installed leisure battery that is running a few other 12v circuits perfectly), nothing on the control panel is lighting up - switching to gas does not trigger the ignition sound, and switching to 240v does not cool the fridge.

Edited January 9 by melon

[Kirk W]

10 hours ago, melon said:

Current situation is, even with 12v being supplied to the ignition circuit (tested both via battery eliminator, and a newly installed leisure battery that is running a few other 12v circuits perfectly), nothing on the control panel is lighting up - switching to gas does not trigger the ignition sound, and switching to 240v does not cool the fridge.

To me it sounds like something that you did when rewiring the refrigerator power has caused a failure somewhere internally but that is only a guess. Since we do not have a schematic for the circuit board, it is impossible to know what voltages should be where other than the terminal block shown in the schematic and I suspect that the white terminal block in the upper left of your picture is what is on the schematic. You might be able to figure out the layout of the circuit board by tracing the foil paths on the back of the board in your picture. As to the fuse, 1.5 ohms is probably just poor meter quality or poor connection as a fuse will normally read 0 ohms when good. Did you remove the fuse from the circuit when you tested it as that must be done for the reading to be accurate. It would not be a bad idea to try a new fuse as Vern has suggested since we are really just guessing. If it isn't the fuse and if there is 12V supply where shown on that terminal block, my next guess would be that the circuit board is bad, but that too is only a guess since I have no service manual or data on the circuit board so have no way to do any valid testing of it. 

[Wrknrvr]

   My next suggestion is to hold the volt meter on the positive and negative incoming power leads.    You must have power there.

   When the unit is turned on there must be a voltage reading like 12.2?

 

  I am saying that to have a good voltage to work with. That must be. If the voltage drops off, then there could be a supply issue.

 

   Pm me with a serial number and model of the fridge.    I am busy as Friday night I may be in -40 degrees weather.

   No comment on that subject.

 

 

[Wrknrvr]

    I want to say that I have voltage issue on my HDT truck and the truck mounted generator.

   There is a voltage issue with the dash start switch to the generator. It is about 10’ from switch to generator.   The voltage drops enough somewhere in the start system, that it makes the solenoid click and the starter grunts.

 

  Low voltage issue.

 

    But if you use the switch on the generator, it starts.

 

   With winter weather in Montana now I am not worrying about the cab start switch at this time.

 

   1970 vintage welder / generator.   Restored it about 6 years ago 

[melon]

5 hours ago, Kirk W said:

To me it sounds like something that you did when rewiring the refrigerator power has caused a failure somewhere internally but that is only a guess. Since we do not have a schematic for the circuit board, it is impossible to know what voltages should be where other than the terminal block shown in the schematic and I suspect that the white terminal block in the upper left of your picture is what is on the schematic. You might be able to figure out the layout of the circuit board by tracing the foil paths on the back of the board in your picture. As to the fuse, 1.5 ohms is probably just poor meter quality or poor connection as a fuse will normally read 0 ohms when good. Did you remove the fuse from the circuit when you tested it as that must be done for the reading to be accurate. It would not be a bad idea to try a new fuse as Vern has suggested since we are really just guessing. If it isn't the fuse and if there is 12V supply where shown on that terminal block, my next guess would be that the circuit board is bad, but that too is only a guess since I have no service manual or data on the circuit board so have no way to do any valid testing of it. 

I'm using this model multimeter - https://www.amazon.com/UNI-T-Multimeters-interface-Backlight-Temperature/dp/B01LXXHJUX

I removed the fuse when I tested it. Will get a new one for testing asap.

There is 13.2v reading at the terminal block, and at the violet/black wires where they are connected to the circuit board.

I'm not sure yet how to test voltages across the circuit board - when i hold one tip of the meter to the negative post on the terminal block, then hold the other tip at various points across the circuit board, most points read 13.2v. Except some points on the very right hand side, where the reading drops down to 4 or 5v.
I don't have a clue if that info is useful or not.

Plan is to test with a new fuse, and if it's still no good, then I'll get in touch with a caravan fridge repair company to ask for a quote on testing the board. I'm just really hesitant to pay for testing if there is a way that I can tell for myself, yes this board is stuffed.

I called a couple of companies today, and unfortunately this circuit board is discontinued.

Thanks again for your help.

[Kirk W]

1 hour ago, melon said:

I'm using this model multimeter

I looked over the meter specs and it should be just fine for trouble shooting what you are.

1 hour ago, melon said:

There is 13.2v reading at the terminal block, and at the violet/black wires where they are connected to the circuit board.

That shows that your problem is not the power supply. That is exactly what you should have.

1 hour ago, melon said:

I'm not sure yet how to test voltages across the circuit board - when i hold one tip of the meter to the negative post on the terminal block, then hold the other tip at various points across the circuit board, most points read 13.2v. Except some points on the very right hand side, where the reading drops down to 4 or 5v.

That is the proper way to measure the voltages. The problem is that we do not know what the circuits on that board are so can only guess at what the voltages should be. To do more you need information about the circuit board and what it has on it. We need a service manual or a circuit board schematic and I am unable to find either of them. 

[melon]

Based on the above, do you have an inkling as to what the problem might be? Or is it still too hard to tell?

Repairing or replacing individual components on the circuit board is clearly beyond me, so if we can say that almost certainly the circuit board is bust, I might need to start working on the “new fridge fund” 😅

But if there is a chance that it might still be a serviceable component, I’m more than happy to continue on this journey.

[Kirk W]

1 hour ago, melon said:

Based on the above, do you have an inkling as to what the problem might be?

While it is only a guess, at this point I would suspect that something was wrong with the way you changed the wiring and that something on the circuit board has failed, but that is only a guess. Additional information on that refrigerator seems to be nonexistent, other than I did find the installation and operation manual online. If I could examine the circuit board I might be able to figure out at least some of the operation to know what to check. The red wire from the terminal block should have 12V as it then goes to the circuit board, in on x103 and out on x104 to the heater and the is return side back to the terminal block. There is something on the circuit board that turns that power on and off as called for. The fact that nothing on the circuit board is lighting up tends to support my suspicion that the problem is on that circuit board. In all probability, a qualified Dometic service tech could probably repair the refrigerator for less cost than to replace it, but that too is only a guess. I'm afraid that this is the best that I can do. 

[Wrknrvr]

   From far  away, my question is?

 

in your picture of the control board, there is a red and I think brown wire on terminals. They are in the middle of the control board.

 

   There is a drawing that shows they both should test positive. So to me that means there is positive power going out to something? Possibly a safety device? I think it needs to pass 12vdc positive power back to the control board. That could be why there is nothing working on the unit.

 

   Just thinking

[Kirk W]

5 hours ago, Wrknrvr said:

 There is a drawing that shows they both should test positive.

The red is positive and the brown is negative. If you look at the full schematic from my link you can see that they supply the 12V heater, with the red positive side passing through the circuit board.

Edited January 10 by Kirk W
add a link

[Wrknrvr]

Without a diagram I cannot follow along.

 

 

 I am busy the rest of the day with weather and medical appointment.

  Will check tonight 

Edited January 10 by Wrknrvr

[Kirk W]

1 hour ago, Wrknrvr said:

Without a diagram I cannot follow along.

Dometic RM7401L Wiring Diagram