Reverse engineering help - Page 1
Forum section: electronics / projects

author: THORs_Hand
author_rank: Contributor
timestamp: November 07, 2017, 04:14:04 pm
content: Hello everyone!Recently i scored a CD mechanism with 3 CD changer from an old sony audio system.I started reverse engineering it today, using it's datasheet and some coffee and here's what i got:The CD assembly itself has integrated all the control logic, this control logic has 2 main chips a CD controller (focus, tracking etc.) and an MP3 decoder. I hacked into it's connector, got all the wires hooked up, ready to roll.The mechanism is relatively simple:it has 2 Chip Enable pins (took me some time to figure this out) CD_CE and MP3_CESPI interface (labled D0; DI; CL)a mute pinanalog audio outputafter getting to this point i realised that i don't have a clue on how to talk to the main chips :|In theory should be this way:CD_CE -> <<Some commands>> after feedback either plays or MP3_CE + some commandsI feel lucky that it has SPI and not other unknown interfaceThe chips i'm talking about are:LC78684E - MP3 DecoderLC78646E (-E?) - CD chipand these 2 were controlled by LC876780B main chip (with integrated VFD driver?)Here are the useful links:http://www.datasheets360.com/pdf/-7041274271229766015- Main chiphttp://pdf.datasheetcatalog.com/datasheet2/0/01qjisq6hxy5oixfw0x93ctsok3y.pdf- MP3 decoderhttp://pdf.datasheetcatalog.com/datasheet/sanyo/LC78646E.pdf- CD chip (Japaneese datasheet was all i could find, seems to be very basic datasheet)https://elektrotanya.com/sony_hcd-gx45_rg440_ver-1.2.pdf/download.html- Service manual of the audio system it came fromCould someone help me to control this thing? What i have available to control it is an Arduino UNO

author: THORs_Hand
author_rank: Contributor
timestamp: November 10, 2017, 08:07:48 pm
content: I just wonder why none of my posts got an answer))Maybe i just take the most complex projects for my level, who knows..

author: jaycee
author_rank: Regular Contributor
timestamp: November 10, 2017, 11:01:51 pm
content: There are two ways to approach this:1) Set up a device (e.g. a scope with protocol decoding, or perhaps a Bus Pirate) to watch the SPI bus and log everything being sent across it. Use the player normally, and watch what it says when you do certain functions.2) Attempt to dump the firmware from the LC876780B, and disassemble it, then analyse it. However, the chip looks like it's a mask ROM version, so there is probably no way to do this.Your chances of getting the detailed datasheets containing the actual command set etc are pretty close to zero.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 11, 2017, 12:04:27 am
content: You don't appreciate how very lucky you are that there is any information available at all for those chips. They are very frequently semi- or full-custom parts with only internal OEM "house-number" identification. As @jaycee said, your only real option is to analyze the communication during normal operation to see if you can suss it out. You have selected a project with a remarkably high ratio of effort vs. benefit.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 11, 2017, 07:05:04 pm
content: These videos are among the very best I have seen on YouTube on the subject of reverse-engineering, especially looking at inter-chip communication (I2C, SPI, etc.) And this guy specializes in very low-cost hardware and open-source software.https://youtu.be/dobU-b0_L1Ihttps://youtu.be/xJ0Mfuj0KUQ

author: THORs_Hand
author_rank: Contributor
timestamp: November 12, 2017, 07:20:19 pm
content: The effort vs benefit thing sounds interesting, but i know that the required work for this could get too much, my purpose is to learn, after all i can always dump it to trash an get some kind of CD playerThe information gained doing this is pricelessIf i just let everything simple and not trying to do anything i'll never be able to do anything by myself, i'll never be able to hack something to do what i want it to do, regardless of device.

author: Richard Crowley
author_rank: Super Contributor
timestamp: November 12, 2017, 10:01:17 pm
content: Quote from: THORs_Hand on November 12, 2017, 07:20:19 pmMost certainly. I highly recommend those videos I cited above (and that guy's YT channel). The stuff he covers in a single video is more than a dozen other YT videos combined. Great tutorials on reverse-engineering and using free software and extraordinarily inexpensive hardware (Chinese logic analyzer clones).