So, from what I've read, the stock HU in the fit is on the low end of OEM stereos, mainly due to a noisy amplifier chips and low quality DACs. Has anyone looked into how feasible it is to just replace these chips? I'm an engineer, so I'm not afraid of tearing apart electronics and replacing components, but I am afraid of wasting a weekend to find out that they are coated in urethane under a riveted box (i.e. not accessible).

If the stereo only outputs 12-bit digital to the DACs, then I can only get a better 12-bit DAC, so the gain there is probably marginal. But amplifier chips on the other hand are analog in, analog out with power, so I can put something together even if I can't find a better chip with the exact same pinout.

I don't want an aftermarket HU at this point purely because I don't have that kind of money. I'd have a lot more fun and only spend $10-20 replacing ICs. Plus it makes me feel like a big man

Any advice, assistance is welcome. Bonus points if someone has a dead HU or some good pics of the circuit boards!

 

I've never looked into it, but it's a very interesting idea . . . If it were something you were willing to do as a service, I think there's a definite market for it - people wanting to keep their stock HU for stealth reasons but want a cleaner output to their speakers and/or amp & sub.

My stock GD head unit is sitting on a shelf in my closet right now, if I get a chance this weekend I'll unscrew a panel or two and see what's easily accessible.

 

I took apart my old Aiwa stereo because I didn't feel like mowing yet, and here's what I found. All the good bits come in TQFP packages, except for one which is the rectangular version. This what there is:

LA1787 - Processor for the radio, not useful

LC7537 - Electronic volume control, seems handy. Accepts a left and right side input, and does the fader, balance, treble, etc. via a 3-wire serial input. Certainly a candidate for noise, but not the only one. Looks tricky to do a drop-in replacement.

LA9241 - Analog Signal Processor for CD Player. Not that useful, talks to microcontroller and turns digital commands into analog for the CD player servos. I think it works with the next part to both digitize the cd signal and then turn it into an analog audio signal.

LC78622 - CD Player DSP. This one seems to be quite important! Houses some more servo controls, an ADC for the CD player signal, outputs digital out for left and right channels but also houses the 1-bit DAC and LPF for the analog left and right. This chip does a lot, and has a lot of serial communication, so swapping it might be a real pain or impossible without reprogramming the whole thing.

LC72358 - This is the microcontroller. It's got instruction RAM, ADCs, etc. for controlling the whole deal. Replacing this is roughly equivalent to building your own head unit.

??6556 - This one was too tough to read, but if it's Sanyo like the rest of the electronics, then it's LC6556, a 5-channel driver. It seems like it's a power amplifier for the servo control signals, not the audio outputs. It has an H-bridge on it, which is for decoupling delicate outputs from motors, which backs that up further.

This is all an aftermarket stereo from 2000, so any usefulness of this information is suspect, but the good news is that everything is easily accessible. The bad news is that we're talking about 48+ pin TQFPs. If the Honda unit has leadless packages, forget it. You can't get those up or down without an oven, or maybe a very delicate and expensive heat gun.

Hopefully, mass production and falling semiconductor prices pushed a move towards more ICs and less discrete components. There are a crap-ton of transistors, caps, and resistors on this board, so the holy grail amplifier could be made of discrete components, making it near impossible to identify without the actual schematic.

If you can get me some nice hi-res pictures of the two board sides and maybe a list of ICs (if they're not readable in the pics), we can see if this thing is worth getting into. OEM has a whole different set of design principles than aftermarket, so I'd say it's still 50-50.