[90SLOWE]

Sad story but Friday the 13th are really starting to get to me.. Last Friday the 13th the clutch on my Mazda broke and last Friday the radio on my E90 330i blew. I filtered the problem down to fuse 31 and here are the details.

Everything on my car is working except the radio and the display. I know the speakers work because I do get the warning sounds. I filtered it down to the fuse and the ones that are related to the radio are 5, 23 and 31. Fuse 5 and 23 have relations to other components as well, which work and I tested them they work fine. Fuse 31 is supposed to be a 20amp fuse but on my Fuse box, there was a 30amp fuse so my guess is, current of the range 20-30amp passed through it and fried something. I am hoping the part that got fried is a secondary fuse and not some major electrical component of the radio. Do our radios have a secondary fuse or did something major blow up? Please help.

I have an appointment on Saturday but want some peace of mind.

[90SLOWE]

any help??

[username604]

Are you under warranty (you mentioned an appointment)?
If you are, then it doesn't matter if the system is fried or the fuse just blew (unless there's some other underlying cause).
Nobody can give you better peace I mind than an actual diagnosis by a specialist (the dealer in your case).

[edirtaynine]

31 is 13 backwards

O_O

[bmw325i]

Dumb question, but did you try replacing the fuse?

[90SLOWE]

Originally Posted by Verbatim

Are you under warranty (you mentioned an appointment)?
If you are, then it doesn't matter if the system is fried or the fuse just blew (unless there's some other underlying cause).
Nobody can give you better peace I mind than an actual diagnosis by a specialist (the dealer in your case).

No I do not have warranty.. It's an appointment at a local shop That works on my car

[90SLOWE]

Originally Posted by bmw325i

Dumb question, but did you try replacing the fuse?

No, I did not replace the fuse because the I checked the fuse electrically (not just visually) and it is fine. However, like I mentioned before, the slot was supposed to have a 20amp fuse but had a 30amp fuse in it.

[90SLOWE]

Originally Posted by edirtaynine

31 is 13 backwards

O_O

Haha, didn't think of that.. Didn't even care about Friday the 13ths until my coworker mentioned it on April 13th and my clutch broke the same day

[scubasteve2365]

Originally Posted by abhi

No, I did not replace the fuse because the I checked the fuse electrically (not just visually) and it is fine. However, like I mentioned before, the slot was supposed to have a 20amp fuse but had a 30amp fuse in it.

I doubt that's thats the problem. A fuse protects you from a short and is sized based on the operating load so that it doesn't blow when there isn't a short (or something near that).

If the fuse was blown and oversized then damage could have occurred, but if the fuse isn't blown than the radio load is simply what it is, the load. A higher fuse rating isn't going to make the radio draw more current, it's just going to allow more current to pass before blowing.

Also, just replace the fuse. I've seen blown fuses that pass enough voltage that make them appear fine but they wouldn't pass enough current. Its rare but I've seen it automotive blade fuses twice on separate occasions in separate vehicles.

[bmw325i]

Originally Posted by scubasteve2365

I doubt that's thats the problem. A fuse protects you from a short and is sized based on the operating load so that it doesn't blow when there isn't a short (or something near that).

If the fuse was blown and oversized then damage could have occurred, but if the fuse isn't blown than the radio load is simply what it is, the load. A higher fuse rating isn't going to make the radio draw more current, it's just going to allow more current to pass before blowing.

Also, just replace the fuse. I've seen blown fuses that pass enough voltage that make them appear fine but they wouldn't pass enough current. Its rare but I've seen it automotive blade fuses twice on separate occasions in separate vehicles.

^ +1

[90SLOWE]

Originally Posted by scubasteve2365

I doubt that's thats the problem. A fuse protects you from a short and is sized based on the operating load so that it doesn't blow when there isn't a short (or something near that).

If the fuse was blown and oversized then damage could have occurred, but if the fuse isn't blown than the radio load is simply what it is, the load. A higher fuse rating isn't going to make the radio draw more current, it's just going to allow more current to pass before blowing.

Also, just replace the fuse. I've seen blown fuses that pass enough voltage that make them appear fine but they wouldn't pass enough current. Its rare but I've seen it automotive blade fuses twice on separate occasions in separate vehicles.

Thank you for the suggestion, I will try that today and let you know what happens. My thought was, the radio is rated for 20A, but the fuse that was placed there was 30A (it must have been opened before, I bought my car used). So could it not have been that there was a power surge from 20-30A, which is above what the radio is rated for, that could have blown my radio? I hope it is the fuse, that would save me time and money.

[scubasteve2365]

Originally Posted by abhi

Thank you for the suggestion, I will try that today and let you know what happens. My thought was, the radio is rated for 20A, but the fuse that was placed there was 30A (it must have been opened before, I bought my car used). So could it not have been that there was a power surge from 20-30A, which is above what the radio is rated for, that could have blown my radio? I hope it is the fuse, that would save me time and money.

Something would have had to create a specific current draw that is greater than 20 but less than 30. I'm not sure of the standards for automative electrical but in industrial electrical delivery your OCPD (over current protection device) is typically rated at 125% of your load, which is considered FLA (full load amps).

If we were to assume that in automotive electrical design, something similar was followed then:

FLA of the radio x 125% = 16 Full Load Amps.

This means that under the most extreme situation your radio is drawing 16A. Its unlikely the radio will ever actually draw that much current. If something occurs to make it draw an excess of 16A (or 20A) then likely it's an unrelated fault.

Often times an OPCD will also be sized not to protect what's attached to it but rather the wire itself. This is why you often see radios with an fuse on the radio body. That fuse is for the radio wherein the fuse in the fuse panel is only to protect the wire that goes between the radio and fusepanel. (Say for instance this wire got pinched somehow and shorted out on the cars frame).

Again, I don't work in automotive electronics, I'm just an electrical engineer that works in industrial applications and these are very general statements from general knowledge about power distribution design.

[90SLOWE]

Tried it, replaced the fuse but it didn't work. Must be a bigger problem

Thank you for the details of how the circuits work.. that was the kind of information I wanted from the forum. Any ideas what I should look for on my own?

[90SLOWE]

Update: The shop told me that it was a bad radio and it has to be replaced. Let me know if anyone is selling the OEM Professional radio

[90SLOWE]

For anyone who might have the a similar problem, I was able to fix it. I tried resetting the whole system by disconnecting the battery for about a minute and my radio is now working