EU Radio Head Unit (EUDM 1991) - Repair

Another radio with intermittent sound output arrived at my desk. It was previously repaired in 2008 but not exactly in top quality.

Attachment 14896

state of repairs 2008

Nevertheless it played fine for 5-20 minutes when it suddenly dropped silent. Different from a previous case regarding a USDM radio the main flex cable connectors where still looking good, so it had to be something different.

Attachment 14893

trouble shooting

As soon as the audio went out, the voltage at the two main output amplifiers was checked and suspiciously low (3.9 V, should be ~10 V). This 10 V supply is generated by the Zener diode ZD807 but measured fine at the diode. As always in such cases, it's best to work backwards. After a bit of tracking and tracing, it became obvious that the 10 supply was fine but somehow did not reach the amplifiers that depend on it.

The reason was quite simple: A broken trace caused a disconnection on the way. After confirming it on an old board and adding a repair wire, the sound came back and was working stable again.

Attachment 14894

an additional (yellow) repair wire

Besides the repair, the power supply PCB had its leaking capacitors exchanged, the volume knob fastened and a flex cable replaced that didn't look very good any more:

Attachment 14895

leaking capacitors on the power PCB

Attachment 14897

a fixed knob

Attachment 14898

a damaged flex cable

Attachment 14899

a cleaned PCB with tracks covered in solder

Attachment 14900.. backside

Attachment 14901final result with all parts re-installed

Attachment 14902final checks

BTW, the really interesting part was that the radio had been to a professional repair shop before and couldn't be fixed. They stated:

"The unit was carefully disassembled and and each part checked according to schematics. It needs to be retuned in an unrepaired state. The audio processor was checked and considered defective. After a long search we found out that it's no longer available."

This raises a lot of questions since the NSX radio doesn't have an audio processor and schematics haven't surfaced anywhere yet. In addition, everything that could be considered a processor in this radio is Alpine proprietary and was never freely available. My guess is, they opened it, couldn't find the issue and simply returned it charging their standard fee ..

PS: Circuit information regarding the 10 V supply has been added to the Radio Repair III page.

Thank you for sharing the info, Heineken. Much appreciated.

So, another one with ZD807 area. I had that years ago.

CUrrently, dealing with one unit with issue somewhere at the middle circuit board.

These days, the audio head unit repair is getting much more challenging ever so your knowledge database is precious.
Once again, thank you.

Kaz

You're welcome Kaz, just trying to share what I've discovered.

Due to the angle the radio is installed and the location of the capacitors, the ZD807 area is affected by damage quite often.
I was surprised by the fact that so many OP amps are supplied with the 10 V reference created there. Even the volume and tone PCB are provided with V+ from there.

Another radio has very strange sound issues probably related to the audio path, too but I haven't been able to identify the problem yet.

It's good to hear the information provided is helping.