help repairing casiotone MT-70


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hi everybody!

I've just adquired a casiotone MT-70 keryboard, and it doesn't work! I've found an IC completely burned and some fails more. So I need its service manual, or schematics, or if someone here has one, his help identifying the IC code.

Thanks!
Gentoo-za
 
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happyrat1

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I wish you luck with that project. The MT-70 was my very first keyboard almost 30 years ago. Mine burned out and became a brick a long long time ago.

I can't find any schematics on Google but chances are you'll also have to replace the electrolytic capacitors as well.

If the chip actually physically burned chances are it's some sort of voltage regulator, either 5 V or 12 V.

Maye you can figure that out by tracing back the leads from the other chips.

Gary
 
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Hi Gary!

I've just found the IC reference written on the board (I didn't notice before! :-D), and as you said it's a power integrated circuit, concretly the LA4138 a 2 channel power amplifier.

I found too, several wires cut off, and the main problem is the cpu and screen (they seem not turning on) I'm following the main DC lines to see if they are correctly feeded.

Some service manual would be great, but I have nothing found yet.

thanks!
Gentoo-za
 

happyrat1

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If you have a scope or a logic probe and the chips are socketed you could always test the chips on a breadboard with a bench supply to see if the CPU is fried or not.
 
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Hi Gary, finnally I solved it (more or less)
the problem with the cpu was a bunch of old wires completely out.
I bought a LA4138 and replaced it, and repaired the wires and now I can play this old synth.
The lcd screen is completely broken, so I see nothing just now xddd But I'm confident replacing it in the future.

I'm gonna take a break and enjoy it now.
Thanks a lot, Gary
 
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happyrat1

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Congrats! Glad to hear that you got it working. Now you have something groovy to keep you amused on the long winter nights ;)

Rock on!

Gary
 
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Hello I can't have LA4138 in shops around me. What can I replaced it with?
 
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