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Today at Atelier Kaz - Private NSX Enthusiast, ex-Honda R&D engineer with F1, Indy/CART background

Bose AMP, Audio Head Unit, A/C CCU Board service 05

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For this week, I have been tackling the OEM head unit that lost the power due to massive acid leakage from the dead capacitors.

It is by far the worst condition that I have ever dealt with.




Addition to the diode and the dual channel OP amp, I found that one of the Zenor diode was dead causing short circuit.
Checked the surrounding components to find out why the zenor died as the series 1Kohm resistor was still surviving and should have limited the current passing the zenor.

As reported earlier, some of the components lost their model number printed on them so it was hard to find any replacements.

For the zenor, there were same circuit used on the bottom board but not easy to read the code even using the digital camera so removed the good zenor from the board and created a simple circuit with my spare resistor to measure the actual zenor voltage.
It was at 6.2V so off to my local electronics shop to get replacement.

I was not sure about the state of the nearby transistor modules and also the OP amp but for bench testing purpose, I wanted to be able to power up the system to measure the signal under live condition.

Re-created the dissolved track using the hard wire and strengthened the CD ACC line for the possible future usage of adaptor such as USA Spec PA11-HON.

I realised that I no longer have the spare PA11-HON so can’t test the CD port for now….
I better place another order to Amazon US.






All big capacitors replaced and new zenor diode installed.

Not sure about the state of some of the surface mounted chips but can’t read the code……




For bench testing with circuit boards out of the head unit case, had to remove the on/off/volume module so will be using thread lock on re-installation.




So, I can now power up the board and the tuner feature is working.
Also, used the cassette tape to check the features.


The signal level from all four channels are somewhat not smooth so connected the Bose AMP and as expected, the sound was bit cracking.
I think either the OP amp was cooked or some of the transistor arrays or other components are dead although at least the transistors looked to be behaving fine.....



It’s a difficult and time consuming task without knowing the actual circuit diagram and yet, you can’t charge too much considering the price of aftermarket audio head unit or even the used OEM one.

I need to speak with the owner to find out how long I can keep this unit but at this stage, I don’t have full confidence in fixing this as all I can do is to replace the suspected parts that I can read the parts code and hope for the ones that I couldn’t even read or recognise the colour….
Parts is very cheap so not a problem…..


Challenge continues.....

The service schedule for other owners need to be revised again with damage to the new window regulator that arrived this week....


Kaz




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Audio

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