RNS 850 black screen and no 51 fuse blown...

SwedishPolarbear · Feb 22, 2021

Hi,

I recently got the black screen and no 51 fuse blown. The dealer wanted ridiculous money to find and fix the issue 😲.
My thoughts are, get the fiber loop thingy, put it on the unit on the rear aft right radio/amp and if culprit, replace with new aftermarket unit (MATCH PP 62DSP).

Does this sound like a workable plan? 🤔
Any and all advice is appreciated.

Thanks
//Polarbear

Troystg · Feb 22, 2021

You have a thread on this black screen so I can go read about it?

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SwedishPolarbear · Feb 22, 2021

Troystg said:
You have a thread on this black screen so I can go read about it?

Sent from my Pixel 4a (5G) using Tapatalk

Hi, no, no thread from my side yet.

But this is what seems to have happened.
During the summer in Sweden we had some very warm days during 2020.
One day the unit did not start as normal and I thought it was due to the heat and I let it cool for the evening.
When trying to start it up the screen comes on for a few seconds before it blinks and goes black.
You can see that it sort of tries to start up the services like radio, BT or Nav, but then dies.
Upon checking the fuse, it was burnet. I put in a new one but that one blew directly indicating some kind of short circuit.

I then contacted the local VW dealer to have them do a first check on what the issue might be (I don't have a VAGCom or similar unit). This is what they came back with:

(Translated):
"There is an event stored with optical databus failed to connect. Check on fuse nbr 51, not okay. Seems to have been short circuited with ground. Recommend removal of trunk liner to be able to measure cables for further investigation."
They wanted me to agree on an extra cost of 800$ for them continue looking for the error... I said no. The first part had already costed me 200$.

So there we are.

Any advice?

//Polarbear

Troystg · Feb 22, 2021

1. VCDS would be cheaper.
2. Can you do any work yourself?
3. You don't know which component failed (3 for non-dynaudio system)
4. Personally I would start with a factory reset.
5. Then investigate the wiring in the back right quarter panel. Might be as simple as wire chafing.

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SwedishPolarbear · Feb 22, 2021

Thanks Troy,

I can do some work, but I am not a mechanic och electronics engineer.

I will tare down the trunk as soon as I have the optics looper and then have a look at any noticeable damage on/around the cables that I can get access to.
I am just wondering what can have chafed a cable that are not close to any moving parts

Could they be damage under the carpet from the front of the car under the mats on its way to the back?
Also, if the cable is damaged, then my suggestion to replace/use a aftermarket unit will not work as it relies on the stock power and speaker cables?

//Polarbear

Troystg · Feb 22, 2021

" Seems to have been short circuited with ground. "

Not the optical cable shorting to ground, it is plastic. It would be a copper wire.. The connection from front to back would be the optical loop not copper so I doubt that would be the problem under carpet.

The MOST / amp box in the rear right has a wiring harness that is a goes toward the fender and has the speaker wires to the doors. Could also be a short at the door for a speaker..

VCDS would REALLY help, and will be useful for any other issue that arises.

Troystg · Feb 22, 2021

Also, there is the dash unit that has a fuse, the glovebox unit that has a fuse and the rear box that has a fuse.... Any of the three go out the MOST buss / ring stops..

SwedishPolarbear · Feb 22, 2021

hmmm, so, a blown nbr 51 fuse can be any of the 3 other units that are either faulty or have a blown fuse by them selves?

As VCDS/VAGCom is a bit further down the road, the "only" option would be to pull out each unit, check the onboard fuse, cabling, shortcut the optics and if no issue continue to the next unit?

I will do some more detailed checks of the backdoors to see if I can find any chafing or similar.

Thanks

//Polarbear

Troystg · Feb 22, 2021

I really don't see it as being a speaker wire in the door (or any where else for that matter) as that would just log a fault code and that speaker would be shut off.

I would look for the three component fuses and check each.

Then inspect the most / amp module in the rear.

Lastly pull the display out of the dash and check it's wires.

The radio tuner and amplifier are in the rear. The dash unit is just controls and display. The glove box is players (cd/dvd, SD x 2, Hard drive) and navigation.

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SwedishPolarbear · Mar 21, 2021

So, I got the fiber looper and the weather was nice enough to start looking at the problem.
I removed the interior, right back in the trunk and removed the radio unit and bypassed the fiber and started the media unit and it came alive 😁.
I looked at all the cables that I could see in the surrounding area of the radio unit, but all looked okay.
I replaced the blown fuse and put back the cables into the radio unit and at once the fuse popped.
So the radio unit is definitely the issue here.

I will see if I can locate a suitable car electrician that can have a look inside the unit for me.

By the way, does anyone know if if can replace the unit with a aftermarket unit straight of? 🤔

BR// Polar bear

Troystg · Mar 21, 2021

Where'd you get the fiber looper?

And glad to see that helped confirm the issue.

Maybe the unit can be repaired by an electronic shop.

Or get a used one from a scrap yard.

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Troystg · Mar 21, 2021

Also ohm out the speaker leads while you have the back open.

Make sure you have good wire runs and speaker coils.

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SwedishPolarbear · Mar 23, 2021

I have opened up the radio unit now and taken it apart with no visible issues burns or marks.
I will check the speaker wires and leads to check if they are alright.

Does a used radio unit need any programing or pairing if I replace it with another used/another one?

Troystg · Mar 24, 2021

SwedishPolarbear said:
I have opened up the radio unit now and taken it apart with no visible issues burns or marks.
I will check the speaker wires and leads to check if they are alright.

Does a used radio unit need any programing or pairing if I replace it with another used/another one?

I've never replaced one but I would think any unit with the same part number would be plug n play.

If you have the back open you can ohm each run from the square connector. Each speaker run should be between 3 and 4 Ohms(guess).

You can check operation of both drivers (tweeter and woofer) by "clicking" a 1.2v battery ( AAA, AA, C, D) across the leads.

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New2Tregs · Oct 5, 2024

tregbn said:
Bump

BOT or not?

Steve_L · Oct 5, 2024

New2Tregs said:
BOT or not?

every chance

Lysy · Oct 7, 2024

Quite odd, 0 posts

New2Tregs · Oct 7, 2024

Lysy said:
Quite odd, 0 posts

I did notice that.
Maybe that's an indication that they're BOTS.

Steve_L · Oct 7, 2024

User's profile is not available. I'd say he's been kicked to the sidewalk.

RNS 850 black screen and no 51 fuse blown...

SwedishPolarbear

Troystg

SwedishPolarbear

Troystg

SwedishPolarbear

Troystg

Troystg

SwedishPolarbear

Troystg

SwedishPolarbear

Troystg

Troystg

SwedishPolarbear

Troystg

New2Tregs

Steve_L

Lysy

New2Tregs

Steve_L

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