Need help troubleshooting a VFD screen problem on my cluster.

Thread Starter

GRNDPNDR

Joined Mar 1, 2012
540
I have this gauge cluster out of my truck and it's behaving weirdly for my 4x4 indicator light.
I will try to explain this as best I can, I just bought this truck and just picked it up yesterday.

First thing to know is that this cluster has a self test feature, when you run it, every single light/indicator on it will light up to show you if there's a problem with one of the lights or screen.
Second thing to know is that when the cluster is powered up outside of the vehicle, it doesn't receive any communication from the 4x4 module and will always show SERV 4WD when power is applied....at least it does on the two 2004 model clusters I have..... this is from a 2005 and is essentially the same cluster.
Third, these are discontinued, as far as I know they can't be purchased or reprogrammed for mileage so getting a new one is out, or finding a reprogramming service isn't where I'm at just yet.

1.) When I test drove the truck and engaged 4WD, the 4WD indicator did not come on.
2.) When performing a self test, the SERV 4WD indicator did not light up, everything else did.
3.) The dealership "fixed" the 4WD indicator somehow, I'm unsure how or what they did but nobody has been in the cluster. When I drive the truck now and engage 4WD the 4WD indicator does in fact come on now.
4.) When doing the self test again, with the 4WD indicator working when 4WD is engaged, the SERV 4WD indicator does not come on still.
5.) When powered up outside of the vehicle the SERV 4WD indicator does not come on.

So I'd really like to fix this and I've tried troubleshooting a couple of things. I've used the cluster from my 2004 in the 2005 truck and everything works as it should.

I've examined the board as closely as I can and I don't see any problems with corroded traces or anything broken.


My next thought is to try and swapping the VFD screen completely, but before I tried that I had another idea and wanted to check here before I went about trying it.
Since I have two of these boards, I wanted to power up the good working one, and jump all 39 pins from just the VFD screen to the VFD screen on the non-working board.

my thoughts are if the VFD screen is good then when it gets power/signal to all the pins it should come on, and work.... if it's broken then this should yield the same results right? with the SERV 4WD indicator remaining off...... does what I'm trying to describe here make sense?

This is from a 2005 Dodge Ram.....could anyone give me any other pointers on things I can check or ways I can troubleshoot this to find out exactly what the problem is because I do believe I've isolated it to at least the circuit board somewhere, if not the VFD screen itself....but then it makes no sense that the 4WD indicator by itself will now work.IMG_8970[1].JPG
 

Delta prime

Joined Nov 15, 2019
373
Hello there . :) I believe it's the VFD itself. The question is it normal wear and tear vibration? I would get an Ohm meter and make some measurements with your known good working unit and compare. I could tell you this something got smoked!



photo_1592095660570.png :)
 

Thread Starter

GRNDPNDR

Joined Mar 1, 2012
540
Hello there . :) I believe it's the VFD itself. The question is it normal wear and tear vibration? I would get an Ohm meter and make some measurements with your known good working unit and compare. I could tell you this something got smoked!

:)
They all look like that, I have 3 of them, and all of the screens have that mark on the corner.

I'm not even sure what to test with my meter....but you know what? I literally just read this in the service manual and had to re-read it....but I'm beginning to wonder if it's actually disabled on my truck as this truck doesn't have electronic 4WD, it has manual shift 4WD.

I kind of feel like an idiot now, but that doesn't explain why the 4WD indicator itself wouldn't come on during the self test.

but yeah, I think I'm an idiot here.
 

MisterBill2

Joined Jan 23, 2018
6,336
How important is it, really, to see the notification or test the display for the feature that you do not have? If that was the only complaint then you are very lucky. And since you have the manual shift version there is no electronic portion to service. So the problem is not real. Re-assemble the cluster before some useful function is damaged.
 

Thread Starter

GRNDPNDR

Joined Mar 1, 2012
540
How important is it, really, to see the notification or test the display for the feature that you do not have? If that was the only complaint then you are very lucky. And since you have the manual shift version there is no electronic portion to service. So the problem is not real. Re-assemble the cluster before some useful function is damaged.
It's actually very important, if that indicator was supposed to work but isn't then I would never know if there was a problem with my 4WD control module.

But since it isn't supposed to be active on a manual shift then it's not important and everything is working as it should be.

the only "discrepancy" is that the 4WD indicator should light up upon doing the test.... or at least I thought it would.

point is it's working, and this information is here if anyone else ever needs it because most people don't have the factory service manual, so this information isn't readily available.

and not one single person in any of the truck groups or forums had this knowledge.
 

MisterBill2

Joined Jan 23, 2018
6,336
If the glass in the display is cracked then it will not work right, either.
If you have a failure in the FWD control module it will be obvious while driving.
Given your apparent level of experience in electronics, and seeing the complexity of that cluster circuit board, even if there was a faulty component how would you replace it, since it is most likely in one of the IC devices? And the ettampt to connect two displays in parallel will probably result in the cluster circuit board no longer functioning. If you damage the cluster that is no longer available then what can you do?
 

Thread Starter

GRNDPNDR

Joined Mar 1, 2012
540
If the glass in the display is cracked then it will not work right, either.
If you have a failure in the FWD control module it will be obvious while driving.
Given your apparent level of experience in electronics, and seeing the complexity of that cluster circuit board, even if there was a faulty component how would you replace it, since it is most likely in one of the IC devices? And the ettampt to connect two displays in parallel will probably result in the cluster circuit board no longer functioning. If you damage the cluster that is no longer available then what can you do?
It's been solved... I'm just a dumbass.

On models that have electronic 4WD the indicator is programmed to work.

On models that have manual 4WD shift (such as mine) the indicator is electronically disabled.
so in other words it's disabled on my cluster because I don't have electronic shift 4WD, the other two clusters I have came from trucks with electronic 4WD.

So if I had actually connected both VFDs to troubleshoot it would have actually worked because it would be sending the signal from a board with that function directly to the VFD....so that would have added further confusion.

At any rate it's all working as it should be and I wasted a bunch of hours of my life troubleshooting something that wasn't broken lol
 
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