Casio WK-1200 Issues: Won't Power On


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Howdy all!

So a Casio WK1200 has flew across my workbench this week, and I'll have to admit I'm a little bit stumped with it.
Service manual for this keyboard can be found here: https://www.manualslib.com/manual/811206/Casio-Wk-1200.html

Simply put, the device won't turn on.
It does receive power, and I've probed a bunch of points on the various daughterboards to check this.

I've tried:

1) Removing the power button, cleaning the carbon contact pad, refitting it. No changes.
2) Cleaning various contacts on chips and whatnot
3) Checked over the capacitors on the board, they appear to be fine (but I don't have tools to test properly)
4) Can't remember where I read it, but apparently holding TONE + Power while booting stops it's power management modes... it did nothing here. Unsurprisingly.

The battery compartment is wrecked, so I'll be repairing that probably tomorrow and testing to see if it runs on batteries.

The power button does appear to be at 12v, which is what IC2 expects on it's input/vcc pin to tell the CPU to turn the keyboard on.
One time during my probing it did "turn on", sort of - the power LED lit up along with the LCD display, but no functionality appeared to work. I have no idea what triggered this. I have a hunch the issue lies in the logic betwixt the power button itself (which operates fine as an individual component) and the CPU's sleep/wake pin stuff... But I'm willing to look wherever if it gets to the bottom of it.

I've just been reading through some bits and will check the voltage regulators, in case the owner accidentally fried something with an incorrect PSU (a lá comments here: https://www.keyboardforums.com/threads/casio-cdp-130-power-issue.31242/)

Any ideas for what and where to check next?

Thanks in advance :)

I'll return tomorrow and edit up this post to be nicer to read
 
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happyrat1

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Look for excessive current draw from a shorted active component.

Overcurrent protection is probably keeping it from booting.

This is common with "soft on" power buttons.

Check for overheating components with an infra red thermometer.

Also, pick up a $50 ESR meter to check the caps in circuit.

Best tech tool invention of the 21st century.

Gary ;)
 
Joined
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Look for excessive current draw from a shorted active component.

Overcurrent protection is probably keeping it from booting.

This is common with "soft on" power buttons.

Check for overheating components with an infra red thermometer.

Also, pick up a $50 ESR meter to check the caps in circuit.

Best tech tool invention of the 21st century.

Gary ;)

Well, I'm building a PC for someone and usually get paid in odd stuff from them... Last year it was a bottle of whisky, this year an ESR meter!

I'll scope it out tomorrow and get back to you. Thanks for the pointers
 
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happyrat1

Destroyer of Eardrums!!!
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Quick test. Disconnect power and check for a short between V++ and GND.

That should narrow it down quick.

Test with the ESR Meter as well.

Gary ;)
 

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