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Radio Head Unit - Capacitor Replacement

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The Radio Head Unit of the NSX suffers from ageing capacitors the same way as many other ECUs in the vehicle. Similar to others it takes about 30 years to manifest itself but high temperature and humidity can cause issues to appear much earlier.
Units that have not been taken care of can become damaged beyond repair and a capacitor replacement should be performed as a precautionary measure even if no problems have been observed yet.

As leakage is typically observed at larger capacitors, circuits who employ these are affected more severely such as power supply and voltage smoothing. Issues can be of varying nature:

  • Increased noise or loss of audio channels
  • Requiring a "warm up period" until operating normally
  • A strange phase-effect like sound between channels
  • The unit won't turn on any more.

In case any of the above issues have been observed, it's likely that damage to other components on the PCB has already happened. In this cases, a clean-up and replacement of the capacitors alone won't be sufficient. Units that won't turn on any more are often broken beyond repair.

To service the unit, two of the three PCBs needs to be removed from the case. To do so, the top and bottom metal cover (secured by two screws each) need to be detached. As a next step, loosen the four screws holding the cassette tape unit in place and lift it straight out of the case.

After turning the unit over, the solder that is attached to the four screws on each corner of the PCB needs to be removed before they can be unscrewed. When done, removal of the screws on the back of the radio holding the antenna as well the CD changer socket is required.
In case of a JDM head unit with it's dual tuner setup, the antenna wire and case ground connection needs to be de-soldered, as well as unscrewing the short ground connection cable.

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CD Changer Socket
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Antenna Socket
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Dual Tuner Antenna and Ground Connection
The PCB can now be lifted carefully, to get access to the white flat cable sockets. There are four of them and they need to be opened by lifting their collars followed by detaching the cable. Removal and inserting of the cable should be effortless and no force necessary. Take care not to loose the piece of plastic attached to the end of the cable as it is required to for a proper fit.

Removal of the power PCB is similar to the cassette deck. There are two screws holding the radio's white main connector to the metal case. After the removal of those two, the small PCB can be lifted straight out of the case.

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bottom PCB (1997 JDM)
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power supply PCB
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main PCB (1997 JDM)

Further disassembly isn't required as the main PCB can stay inside the case for all further steps.

Replacing all electrolytic capacitors inside the head unit would be a huge task. As small capacitors typically don't suffer from leakage and could be used in areas where specific characteristics are required, the suggestion is to replace only larger capacitors - identified by the metal imprinted cross on the top (the venting crack).

To improve robustness it's advised to use capacitors with a higher temperature rating than those originally installed. The factory rating states a lifetime of 1.000 hours at 85 C. An improved replacement should be rated 1.000 h at 105 C or more. Note that increasing both the maximum temperature as well as the lifetime rating results in an overall improvement.
To avoid any damage due to leakage, dry (Aluminum Polymer) capacitors can be used as a replacement. Their price is significantly higher but guaranteed to be safe for the PCB even in case of failure.

Multiple revisions of the layout and changes during different production years exist. Therefore the capacitors need to de identified an a case-by-case basis. A rough expectation is about 10-12 pieces from four categories.

When selecting an appropriate replacement, it needs to be ensured that the capacitance is exactly matching. Voltage ratings can be exceeded without side effects. In addition to electrical parameters, mechanical properties need to be considered. If space allows, larger size capacitors can be installed but that should be checked carefully.

The best way to remove the old capacitors is to use a professional de-soldering gun. De-solder wick or a manual de-soldering tool can be used, too. The soldering iron should be electronically controlled as a fixed wattage type can have trouble with larger copper areas.

For details on how to treat and repair areas affected by acid from the capacitors (either turning the PCB's green silk screen darker or lighter in colour) please check the corresponding article about capacitor replacement at the Climate Control Unit (CCU) for details. Parts affected by acid can potentially be damaged, as it has been observed in several cases.

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bottom PCB (1997 JDM)
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power supply PCB
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main PCB (1997 JDM)

Re-assembly is the reverse of disassembly. The flat cables and their connectors can be tricky to re-attach, though. The preferred solution is to attach them to the bottom PCB first, run them through the case and then attach them to the main PCB but it remains a bit of a tricky task.

Proper repair should be followed by a test run for a few hours as well as checking all functions of the unit. Everything should work fine, even when driving on bumpy roads, for a proper and long lasting repair.

Updated 26-02-2022 at 03:48 PM by Heineken

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