2 Questions regarding s3c8454x29-qw84 8 bit microcontroller controller

[tedsorvino]

Hi everyone.
A friend gave me an older cheap-ish electronic piano for repair. After a bit of research on the 2 main boards, obviously the problem I realised was a microcontroller ic  s3c8454x29-qw84. It was getting smoking hot in seconds. Replaced most things around it, but I can’t find the ic itself.
So I would like to ask you

1) Do I need any kind of particular code to flash on it or is it working on its own? If something needs to be flashed I guess it’s game over.
2) In case it works autonomously, what would be an exact more modern and readily available substitute?

Thank you in advance

[pcprogrammer]

The datasheet shows it to be a mask programmable device that also exists as a ROM less version, so it depends on what is used in the electronic piano you are trying to repair.

If it is mask programmed you are basically out of luck. If the device uses an external ROM you can search the web for a replacement s3c8454x29-qw84.

As it is a "simple" microcontroller it could be replaced with something more modern, but that would require recreating the full functionality of the original program that ran in the s3c8454x29-qw84. Could be fun, but most likely not worth it.

Maybe if you provide some details* about the piano, it might be that someone can offer better help.

* Like make and model or even the service manual if you have it.

[tedsorvino]

Thank you pcprogrammer.
The piano is a cheap chinese near “no name” 90s console piano. I doubt that there is any particular site where any service manual, user manual or software can be found. No worth, but I just help a friend.
Since I’m a relatively experienced repair person on keyboards, the microcontroller use on that daughter board works as a note on and note off message sender to the main board. Actually replaces the classic old analog ideas of flip-flops and other voltage controlled circuits. Even digital decoders are more common in that are.
Could you please help me to locate a version without mask rom? A bit of wishful thinking that the rom is based on the other similar (and bigger) chips on the main board.
Unfortunately I can’t find it anywhere on eBay or aliexpress. I’m eu based but the source location doesn’t really matter.

[pcprogrammer]

I'm just a retired hobbyist and have the same google or what ever search machine at my disposal, so can't help you with finding that part.

I doubt that you will be able to make it work even if you find the same but rom less microcontroller.

Take some good pictures of the boards inside the piano and post them here, so I can see if there is some way of thinking up a solution to make it work again, just for the fun of it.

[tedsorvino]

Thanks Pcprogrammer. I will do. Actually I’ve left them at my friends place after the initial testing. So I will ask for the. I know the ic so I will mark it on the pictures.

[tedsorvino]

Update.
The digital piano is branded HP 66 DIGITAL PIANO.
It’s  a generic Chinese console piano that is named differently (piano ova, piano star, La acoustics etc etc) . But it’s always HP 66.
No detailed info about its manufacturer can be found anywhere. No official web site and support.

Here are some pictures.
One is the faulty microcontroller.
Two is the board where the microcontroller is attached. It’s the only microcontroller on that slim long board. It’s the keyboard board. Note on-off messages.
Three is the piano main board where the other board is attached.

If you have any idea I will be very happy to hear it
Thanks for your time.

[pcprogrammer]

Thanks for posting the pictures.

For what I can tell of it the board with the troublesome MCU is for scanning the key presses, and this should not be that hard to implement on another MCU. If I'm correct, the other side of that board has a lot of small diodes on it and is capable of sensing key velocity, by measuring the time between two different contacts making contact in following order.

It depends a bit on how the two systems pass information to make it all work, so some reverse engineering will be needed. The question is also if the other two boards are still fine, and if it is really worth the time and effort to get it working again.

When I search for this HP66 DIGITAL PIANO, I see a full size standing piano with pedals and 88 keys, while the board with the MCU only has provisions for 48 keys (4 octaves), so is there another board with those rubber pads that connects to this one?

Based on the needed number of pins of the MCU a replacement scanner board could be constructed with some STM32 MCU board like a 64 pin WeAct STM32F412, F405 or F446 board https://www.aliexpress.com/item/1005006051651136.html or if more IO pins are needed a STM32F407 board like this one https://www.aliexpress.com/item/1005001603853562.html. To interface with the other boards level converters might be needed to go from 5V to 3V3 on which the STM32 MCU runs.

It can be a fun project and code wise not that difficult.

[tedsorvino]

Thanks for the reply pcprogrammer

“For what I can tell of it the board with the troublesome MCU is for scanning the key presses, and this should not be that hard to implement on another MCU. If I'm correct, the other side of that board has a lot of small diodes on it and is capable of sensing key velocity, by measuring the time between two different contacts making contact in following order.”

Yes indeed. This is exactly how all digital keyboards “keybeds work”. Actually, this is super cheap since it only has 1 sensor. Meaning that sensor contains both on-off and velocity messages. Usually 1 sensor means no velocity sensitivity. But this had some (not all values but some like 10%-30%-60%-90% or so)

“It depends a bit on how the two systems pass information to make it all work, so some reverse engineering will be needed. The question is also if the other two boards are still fine, and if it is really worth the time and effort to get it working again.”

Can’t tell. I think there is some kind of code about transforming even the velocity messages digitally. Really feel like it’s not worth it.

“When I search for this HP66 DIGITAL PIANO, I see a full size standing piano with pedals and 88 keys, while the board with the MCU only has provisions for 48 keys (4 octaves), so is there another board with those rubber pads that connects to this one?”

Yes that’s the case. There is another board. No mcu there.

“Based on the needed number of pins of the MCU a replacement scanner board could be constructed with some STM32 MCU board like a 64 pin WeAct STM32F412, F405 or F446 board https://www.aliexpress.com/item/1005006051651136.html or if more IO pins are needed a STM32F407 board like this one https://www.aliexpress.com/item/1005001603853562.html. To interface with the other boards level converters might be needed to go from 5V to 3V3 on which the STM32 MCU runs.

It can be a fun project and code wise not that difficult.”

Have to admit that coding and the digital world is not my cup of tea at all. If it’s super easy I would try…but if not…let’s say it’s finished.
This is the site of a local digital spares - arduino store. https://grobotronics.com
Can you see anything that could work like the ones from aliexpress?

[pcprogrammer]

The Compatible Mega2560 Pro board https://grobotronics.com/compatible-mega2560-pro-ch340.html could do the trick, but like I wrote, the first thing to do is reverse engineer the keyboard scanning hardware into a schematic to get a sense of the scanning matrix and the connections to the other boards.

Benefit of the Mega2560 is that it runs on the same voltages as the original S3C8454 MCU.

If the board is still functional a bit, the data exchange between the two boards could be examined with a simple USB logic analyzer, but I could not find one on the store you mentioned. Something like this https://www.aliexpress.com/item/1005009062074562.html

The code for this is simple and can be written with the Arduino environment, which fits more with the Mega2560 board.

All that is needed is a loop that outputs a scan pulse and reads the return lines to see if any of the keys is pressed. The velocity sensing can be done by capturing a free running timer value on the first contact of a key and again on the second contact of the key. Take the difference of the two values and use it as the velocity. Might need some scaling to match what the main boards want.

Another option to avoid the interface between the keyboard scanning board and the sound generation boards, is to make use of MIDI. Have the new keyboard scanning device output the note on/off information via MIDI. There are plenty examples on the net on how that can be done with the Arduino boards.

To keep the existing MIDI interface of the piano in use for the external world a MIDI merger can be incorporated into the setup.

[tedsorvino]

Really thank you for that Pcprogrammer, but I have some other projects that I’m way more familiar with and I don’t think I can overtake something that is far removed from my knowledge.
I wish there was a spare pcb, or a logic ic replacement…the rest is beyond me.
 Usually when something like that happens to such cheapo things it’s always pcb replacement maximum.
I will check the traces soon and I may come back with a schematic. I will speak to my friend and see what he decides….
I’m thinking about suggesting a used88 keys midi controller. Not very expensive. Easy and simple.

Anyways I do really appreciate your tone and effort.
Thanks again.

[pcprogrammer]

I’m thinking about suggesting a used88 keys midi controller. Not very expensive. Easy and simple.

Yep, that is also an option. Take out the sound boards and the power supply and put them in a small case and call it a day.