Today at Atelier Kaz - ex-Honda R&D, F1, Indy/CART engineer

And just when I thought I can go out for the test driving session, suddenly, I lost all the audio sound from the head unit.
While working on other area of the car, I was playing radio with and without engine running.

I checked the AMP relay plus the fuse and both were fine.
I could hear the faint hiss from all 4 speakers so the AMP itself was powered up but no input signal from the head unit.

So, no option but to take the audio head unit out of the cabin again and tested on the bench.
I already knew which circuit to look at as I saw similar issue in the past.

It confirmed that it took out one of the zenor diode and very likely to have damaged nearby transistor array because
the signal quality at certain frequency range was very poor, like distorted.

For example, when you are listening to the news, the frequency range of the voice is mid/high only so it sounded fine.
However, if you listen to music like pop, rock, etc, the low range frequency was distorted and unpleasant listening experience.
With classic music, depending on the instruments used, some part of the music is distorted but others were fine.

Any way, I must find out the cause of the issue as it was fine when tested on the bench for more than 2days.

I have another head unit that one owner left with me many years ago and it had much more severe damages but
showing similar poor signal quality issue.

From time to time, when you fix one issue and the components start operating at full spec, it could highlight hidden issue in other area
especially when you introduce all sorts of noise from ACG, IG coil, etc.
I think this is the reason why it didn’t fail when being tested on the bench for 2 days and yet it failed in very short time on the car with
many engine fire up and battery power cycle.

Without knowing the exact cause, there was no guarantee that the same issue won't happen again so proposed the owner to
refurbish the original JDM head unit that the owner installed before bringing the car to my place.
On the way to here, the owner told me that he heard loud ‘pop’ and lost the right door speaker sound.

Previously, the owner didn’t want to refurbish this unit so I decided to do it for free of charge as the other unit failed when I thought I fixed it.
Also, at that point, I thought I had better chance of fixing the JDM unit as it was working but lost right door sound so both myself and the owner thought
it was typical Bose speaker AMP failure and not the head unit.











Well, when I opened this JDM unit, it showed severe damages.
It even contaminated one of the IC as well although the nearby OP AMP was fine.


On the bench, unfortunately, it confirmed that the faint signal level at both FR and RR channels were caused by the damages inside the head unit and
not the Bose AMP at the right door.











Later, I found out that the faint right signal issue won’t happen when in CD mode but with radio and cassette.
So, based on the signal quality and reliability point of view, decided to keep this JDM unit on the car for now.

I hope I can find some time this year to look into the poor signal quality issue so that I can recover extra audio head units for the owners.