Looking for fried IC in a Yamaha DGX-505 keyboard

[boogyman19946]

Hello guys,

I'm new to the forums, and I've happened to come across it in search for a solution to my current problem.

A while ago my dad took his keyboard with him on a camping trip and his genius idea was to use the juice of the car battery to power up his keyboard. So he plugs in his machine into the battery and it looks like the keyboard is working. As soon as he touches the keys, the keyboard says thank you and the only thing remaining is the blue back light from the LCD.

It's a nice keyboard (compared to the one I have now anyway), and I was hoping that perhaps its life hasn't come to an end just yet. So I grab my handy dandy screw driver and rip this baby apart. Inside I find the power supply, various PCBs interfacing the buttons and the LCD, and behind them all the brains of the operation. Aside from the main PCB, the other circuits are all analog and I imagine they are the least likely to be the ones that got fried. The main PCB holds all the ICs and if there is anything that's over sensitive to excessive power I figured it's the chips. The only problem is, I don't really know how to check which chip is fried. I've tried looking up their datasheets but I guess Yamaha uses some kind of off-grid chips. I could figure out some of the functionality of the chips, like for example the chip to which every other chips is connected is most likely the main microcontroller, other chip connecting to the actually keys would be the "decoder"(for a lack of a better word). However, I don't see how the function helps as I still don't know which chip is actually faulty.

My question is, is there any practical (or impractical I guess >.>) way to check which IC actually fried? From what I read chips can actually burn only partially so whereas some functions work, others might not.

Any help would be appreciated

EDIT: Here are the pictures of the PCBs

Main PCB front:

Back side:

PSU:

If you guys need the other side with the connections I'll upload that too. Also, there is a chip screwed to the back of the metal heatsink.

The remaining boards are just wired connections with no components on them.

 

[davenn]

yup they can fry internally would out any obvious visible external stress

a couple of close up and sharp pics of the various boards would give all an idea to what you are describing
From there some one may be able to suggest testing paths to follow

Dave

 

[boogyman19946]

Alrighty, I'll try getting some shots of the PCBs over night I'll edit the main post with pictures of the various stuff in there

 

[boogyman19946]

Pictures added to the main post

EDIT: I was not aware of the actual size of the images... That is some uber high def right there XD

 

[davenn]

hahaha yup it does pay to resize images before posting 800x 600 as a shear max

I cant see any obvious signs of damage, with that much LSI (large scale intergration)
you may be fighting an unwinable battle, specially without any cct or service info.

Dave

 

[boogyman19946]

Through some guess work I've arrived with a conclusion that it's most likely the microcontroller that got fried. Either that or it was a whole bunch of chips that got fried. From what I understand, the structure of an electronic such as this, there would be an EEPROM to boot the "system", flash to keep the sound banks and such, a micocontroller to organize the mess, and other chips allowing IO to and from the device. Since the display was working before fried, I take it that it was most likely the microcontroller that went to hell since with the press of the keys, everything went out. If it was any part of the chips outside of it, the circuit would be still operational with the exception of that part, but at the same time, everything died. There was no sound, no display, no nothing. So, either a whole bunch of chips fried at the same time, or the microcontroller went out. I'm not particularly experienced with electronics but, as a games programmer, I do get quite an exercise finding bugs I'm just not sure how different the environment is between the two practices that's why I need help from peers experienced with the problem at hand =]

 

[davenn]

like I suggested without good service data your chances are very slim.
you would need info on what every single pin of each of those chips did, the signals you would expect to see on them when using a oscilloscope etc
Even if you discovered a particular one of those chips faulty, the chances of getting a replacement are even slimmer.
The bootup routines could most likely be stored in the microprocessor itself.

sorry to sound a bit negative, but unless you happened to find one of the standalone resistors, transistors, diodes etc faulty, its likely to be a throwaway unit

Dave

 

[boogyman19946]

Oh no don't worry about sounding negative. I was just hoping that something at least could be done.

One more thing though.
I do have another keyboard, also from Yamaha, which may be a little bit similar in structure (I never really took it apart). The broken keyboard, however, has 88 keys and the working one has 76 (I think). Is there any remote chance to have the brains of the 76 key instrument in the 88 key package?

EDIT: I just peeked inside the 76 key keyboard and I think they use the same microcontroller (I didn't get too close of a look at it but they look almost the same and with the same YMW767-V code)