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Heineken's Garage

Radio Head Unit - Repair I

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Introduction
Issues with the radio head unit is a common fault, affecting nearly all NSX depending on age and climate zone. Capacitor replacement should be the first step to perform, followed by further analysis and repair.

Diagnostic
The following error cases and ways of repairing have been identified so far. Almost all of them are caused by capacitor leakage but not exclusively since the radios suffer from normal wear and tear similar to other consumer audio electronics.

Radio doesn't turn on I
Observed on: 2 EUDM Radios
Fixed by: Trace repair
Status: Fully understood

Usually the worst report. If acid damage from leaky capacitors manages to reach the proprietary Alpine CPU and cause damage there, not much can be done since these are no standard parts.

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a badly damaged PCB that would not turn on

With power supplied to the radio (but radio turned off) and with the bottom part of the metal housing removed, check pin SCK at the right hand 16 pin (EUDM) or 14 pin (JDM) flex cable at the back of the radio (connecting the lower PCB to the middle PCB).

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pins (EUDM)
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pins (JDM)

It should show groups of seven 5 V rectangle pulses, every 15 ms which indicates that the microcontroller on the middle PCB is alive and communicating:

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Signal indicating a working controller

Next measure the signal on pin P.S (EUDM) or POWER (JDM). It should be 5 V and go down to nearly 0 V while pressing the ON/OFF button. If 5 V is not reached, it would indicate an issue with the internal power supply. If the 0 V are not reached a problem with the signal path can be considered.


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Correct signal when pressing ON/OFF

Now check the POWER pin (JDM) at the Volume knob flex cable connector (on EUDM radios, it's the same pin but unlabeled). It should behave the exact same way as the pin at the 14/16 pin flex cables.

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Pins (JDM)

The two pins previously checked are electrically connected. Measuring the resistance between them should yield a value of <1 Ω. A higher value indicates a broken trace or VIA on the PCB. Often it's the lowermost line from the volume knob flex cable connector to the first VIA:

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broken trace hidden under the capacitor's paint marking

Radio doesn't turn on II
Obser
ved on: 1 EUDM Radio
Fixed by: -not fixable-
Status fully understood

If the repair under "Radios does not turn on I" wasn't successful or not required, other reasons are possible. The middle PCB processor is responsible for controlling the display and the start-up procedure. He creates and monitors the ON/OFF signal that is routed to the lower PCB and to the ON/OFF button.

The middle PCB can be checked independent of the lower PCB. To do so, remove the lower PCB and the tape unit. Measure the top left pin of the left flex cable connector to ground. It should measure 5 V.

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This pin is the ON/OFF (P.S pin) signal mentioned under "Radio does not turn on I". When briefly connected to GND, the middle PCB starts up and illuminates the display with the TAPE message (or 78.5 MHz if a tape unit is installed). Connecting the pin to GND a second time will switch-off the middle PCB - identical to the Power ON/OFF button.

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If the display is not lighting up, the middle PCB is damaged. During "Radio does not start up I" we checked the SCK pin on the lower PCB and the 5 V on the power signal which confirms, that the middle PCB processor is generally working.

When manually turning on the middle PCB (via the ON/OFF signal), pin 6 of the middle PCB processor needs to rise - it switches the display power supply. If this pin does not rise, the processor pin is considered broken and a middle PCB replacement required.

The lower PCB can only be tested when connected to the middle PCB - use a known working middle PCB since there have been cases where both PCBs were damaged. If the middle PCB works correctly, it will send a pulse to the NMI pin of the lower processor (pin 28) - the processor will start, which can be observed on pin 16 (clock).

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yellow: NMI (wakup)
blue: processor clock

It will go right back to sleep after ab about 200 ms unless there is a high signal on pin 62 - also sent by the middle PCB. If the processor goes to sleep after 200 ms despite having a high signal on pin 62 - consider the processor broken, requiring a lower PCB replacement.


Note: Page limit reached. Further repairs on Radio Head Unit - Repair II

Updated 12-07-2023 at 09:15 PM by Heineken

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Comments

  1. Heineken's Avatar
    Update: Added info about repair of Too little Volume and Distortions increasing with Volume
  2. Heineken's Avatar
    Update: Added further information on how to test the middle PCB without the lower PCB and general startup procedure involving both processors.
  3. wixer's Avatar
    Another fine job Lars.
  4. Heineken's Avatar
    Quote Originally Posted by wixer
    Another fine job Lars.
    Thank you very much - unfortunately the radio where this info is from couldn't be saved but learned many new things about how the innards work.