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EU Radio Head Unit (EUDM 1991) - Repair

Joined
5 August 2014
Messages
201
Location
Germany
Another radio with intermittent sound output arrived at my desk. It was previously repaired in 2008 but not exactly in top quality.

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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.

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trouble shooting and tracing

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.

Click image for larger version. Name:    PXL_20240106_185608078s.jpg Views:    0 Size:    137.8 KB ID:    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:

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leaking capacitors on the power PCB

Click image for larger version. Name:    PXL_20240107_183530256s.jpg Views:    0 Size:    77.0 KB ID:    14897
a fixed knob

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a damaged flex cable


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a cleaned PCB with tracks covered in solder


Click image for larger version. Name:    PXL_20240114_161450790s.jpg Views:    0 Size:    66.1 KB ID:    14900
.. backside

Click image for larger version. Name:    PXL_20240114_163025394s.jpg Views:    0 Size:    92.0 KB ID:    14901
final result with all parts re-installed

Click image for larger version. Name:    PXL_20240114_170434362s.jpg Views:    0 Size:    93.6 KB ID:    14902
final 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.
 
Another radio with intermittent sound output arrived at my desk. It was previously repaired in 2008 but not exactly in top quality.

Click image for larger version. Name:    PXL_20240107_183852196s.jpg Views:    0 Size:    120.6 KB ID:    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.

Click image for larger version. Name:    PXL_20240106_180125647s.jpg Views:    0 Size:    91.2 KB ID:    14893
trouble shooting and tracing

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.

Click image for larger version. Name:    PXL_20240106_185608078s.jpg Views:    0 Size:    137.8 KB ID:    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:

Click image for larger version. Name:    PXL_20240107_182422748s.jpg Views:    0 Size:    91.9 KB ID:    14895
leaking capacitors on the power PCB

Click image for larger version. Name:    PXL_20240107_183530256s.jpg Views:    0 Size:    77.0 KB ID:    14897
a fixed knob

Click image for larger version. Name:    PXL_20240107_183800961s.jpg Views:    0 Size:    58.1 KB ID:    14898
a damaged flex cable


Click image for larger version. Name:    PXL_20240114_161442997s.jpg Views:    0 Size:    62.8 KB ID:    14899
a cleaned PCB with tracks covered in solder


Click image for larger version. Name:    PXL_20240114_161450790s.jpg Views:    0 Size:    66.1 KB ID:    14900
.. backside

Click image for larger version. Name:    PXL_20240114_163025394s.jpg Views:    0 Size:    92.0 KB ID:    14901
final result with all parts re-installed

Click image for larger version. Name:    PXL_20240114_170434362s.jpg Views:    0 Size:    93.6 KB ID:    14902
final 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.
Well done Lars. Now......if only mine was that simple!!!
 
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