Dead Casiotone MT-65 help?

[grandpa]

I picked up a Casiotone MT-65 quite cheap at $5AUD (about $3.30US). When I got it home, plugged it in and flicked the off/on switch, nothing... Nothing at all. No LED activity no "pop" of the amp circuit. So I cracked open the case to have a look with my limited knowledge, hoping it was something easy to fix and noticed one of the chips on the power supply board looks like it has burnt out.





Now, I have bent a handful of toys and keyboards, nothing to technical though, as I am not an electronics expert. I would love to make use of this keyboard. I have fixed a few of my keyboards before, but just easy things like bad pots, broken connections and such. Can anyone help me out? Fixable? I was planning on bending it...

[Circuitbenders]

Well that LA4138 looks alright to me, its just got a rather messy looking heatsink on it. That three legged thing on the second photo labelled D325-E2K looks like a voltage regulator to me so you might want to check that you are actually getting anything on its pins with a multimeter.

The first thing i'd check with all casios of this era is that the power socket is actually working in the first place!

[grandpa]

Oh, so it looks ok. I just saw it was black and thought it might have burnt out or something. When I had it open, I bypassed the power socket and still nothing. I don't actually have a multimeter currently, but will give it a check asap.

[Circuitbenders]

Hold on, is that actually the power supply area? I only ask because i've just checked the datasheet for the LA4138 and its a 2 channel power amp, which explains the presence of the heatsink. That shouldn't have any effect on if the thing turns on or not.

[ne7]

two things - this is gonna sound very silly:

but have you checked the on/off switch - i recently got a KB and the on / off switch was toast and just bypassing it fixed it... also have u tried it off batteries - and have you given the power socket a good clean? sorry if thats super obvious mate!

ne7

[Gordonjcp]

"D325" means "2SD325" - you can probably work out the codes for other transistors.  Japanese kit seems to use "nSlnnn[n]" formats, like 2SD325, 2SC1007, 3SK135 etc.

A big power tranny like that could be used as a regulator.  Is that a Zener diode beside it, partly hidden by the big electrolytic?