1998 740iL ::: Radio & Cass Not Working ::: CD Works

Hello Sam,

I once had a simular problem with a E39 BMW car radio. This one gave max volume to the right front speaker. The problem was a NVM (24C08 or equal) IC inside the radio. This was working incorrectly, 0's were at some locations set to 1. To solve open the radio find the IC, solder it out. Copy the current contents to a new IC, put that in the radio. Next it should be ok again.

It's quite a specialist job, but a hobbiest with a eprom reader/programmer can also do it.

Best regards, Marcel, '92 525i 340.000 km.

Thanks man ... but that is just beyond my scope and capabilities. So the culprit is the radio not the cassette deck ... right?

Hopefully you are aware that the 740iL has a Cass Deck Unit ; a DSP; Radio and an Amplifier Unit ... it is a fairly elaborate setup ... I am not sure how that compares with the 525i ...

In any event, Thanks for the response.

Perhaps I can try and purchase a used radio/unit on eBay or something ...

Cheers,

Sam

Can't manage to understand how reading the corrupted contents of a 27C08 allowed you to reprogram correctly another chip. Unless you've the source on a readable media. May you provide a little bit more elaborated explanation please ?

TIA

Hello,

What I saw when I read the eprom from a location, the value was always 0xF0. So the first 4 bits were always stuck to 1, the lower bits vary. I read the eprom, wrote the old data into the new eprom. I think the permanent stuck to 1 occured by reading/writing the value's to many times. Normally they are in the spec of an IC.

The software inside the radio reads the value, if the value was not correct/changed it tries to overwrite it with the correct value eg 0x10. A sort of range checking.

Best regards, Marcel

Thought I'd post this info from a separate thread I had going with a shop that does this for a living ... It would appear that in my case at least, the problem is the cassette deck and NOT the radio or amp ... While he did not indicate exactly what is wrong with the cassette deck, I suspected something like this ... because the radio "appears" to scan etc ... i.e looks to run but no sound ...

It behaves almost like it thinks that I should be playing the cassette tape not the radio ... something in there is "tripped" ...

Here is the message from Radioman Inc., staff to me ... I picked his link from my local BMW Club Chapter Site .. I will report on the progress ... or resolution ...

The cost of repair is $175 and takes a few days. send in the cassette unit. Our warrantee is for one year. Ship to:

Radioman Inc.

John <

Hello,

What I saw when I read the eprom from a location, the value was always 0xF0. So the first 4 bits were always stuck to 1, the lower bits vary. I read the eprom, wrote the old data into the new eprom. I think the permanent stuck to 1 occured by reading/writing the value's to many times. Normally they are in the spec of an IC.

The software inside the radio reads the value, if the value was not correct/changed it tries to overwrite it with the correct value eg 0x10. A sort of range checking.

Best regards, Marcel