Powering Up Toyota Audio Head Unit (86120-08010)

It appears two of my salvaged LCDs might have come from the same product, with identical (or nearly so) interface and command protocol. That is great, but I don’t know what that protocol actually is. It isn’t terribly promising as a starting point, so I decided to continue looking in my pile of salvaged electronics. Next candidate is the LCD embedded in the control panel of an automotive audio head unit. This was a stock tape deck from a 1998 Toyota Camry LE, which was replaced by an aftermarket deck for modern conveniences like Bluetooth audio. It was one of the retired pieces of equipment I brought to the January 2020 session of Disassembly Academy and taken apart. All metal pieces went into recycle, all plastic pieces went to landfill, and I kept the electronic circuit boards.

Since the metal external panels are gone, I no longer have the model number. Searching through eBay listings, I guess it was a Toyota 86210-08010. This listing explicitly mentioned Toyota Camry in their description. However, I saw several other Toyota units that looked superficially similar but with different numbers, like this 86120-04090. I thought maybe I’ll just call it “86210” but there are “86210” units that look wildly different like this 86120-2B761. Clearly there are complexities in Toyota parts numbering that I don’t understand, but for now I’ll go with 86210-08010.

The reason this particular LCD is interesting is because it is part of a still-intact control board. I’m optimistic that I could figure out enough of the control board to make it do my own bidding.

The backside of the board has a large identifier: 121941-4890D700. That didn’t turn up anything, but there are two other features on the back that make me optimistic.

The first is a clearly identified chip: Sanyo LC75853N and a search found its datasheet. It is a LCD controller with additional capability to scan for button presses, which makes sense for use in a control panel like this one. Furthermore, the datasheet should describe the control protocol.

Even better, the board has a connector to the rest of the radio, and it looks like all the pins are labeled. Some of them were cropped at the bottom and even if they weren’t cropped, I don’t necessarily understand what they all mean. But GND and ACC5V are clearly legible, which is a great start. What more can I ask for? Well, I can ask for it to be powered up and running so I can probe those pins in action.

When I replaced this head unit, I recall going online to purchase an adapter wiring harness and a pinout guide to know which wire went where. Many Toyota head units shared the same connector and pinout, so this diagram for a slightly different model was close enough.

I could buy another wiring harness, possibly this unit, but decided against spending more money. This is for experimentation and I could easily solder directly to the circuit board.

It probably didn’t matter very much in this case, but I also thought I’d follow wire color convention for automotive audio. I connected the “battery” (yellow) and “accessory” (red) wires up to +12V on my bench power supply, and black wires to ground.

The screen comes alive! Very nice. From here, I started disconnecting power wires and found that for purposes of powering up the control panel I only really needed half the wires, the three on the central connector. (Visible in the back of this image.) With a screen that is alive and kicking, and a datasheet that should explain everything, I expect a high probability of success for learning how to master this control board. This could be an interesting project, and the only problem is that it veers very far from Joey Castillo’s Remoticon talk which motivated me to look at LCDs. I set aside this project for later and started looking for simpler LCDs in my pile.

[UPDATE: I have returned to this device and made great progress on the second try.]

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