DipSwitch
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Bucks County, PA

Hey all!

I've been tinkering with this SK-10 I picked up at a yard sale a few days ago. I was hoping to bend it this weekend, but instead have wrestling to get it to power on!

After trying fresh batteries and a 7.5v AC adapter, I opened it up. Nothing looked unusual, but after a nice cleaning I still wasn't getting any response from the keyboard.
I've followed the power voltage, and I'm pretty sure it's as it should be. I replaced the T1 Transistor with a similar NPN as suggested by this service manual because it was reading a bit funky-- no signs of physical damage though. (The manual is for a SK-1, but I can't find the SK-10, and the boards run relatively similar). All the caps look fine, and aside from a bit of resin on the CPU, everything looks brand new.

Any thoughts? Anyone see anything like this before? As far as I can tell, everything else seems to be working correctly.

I've done quite a bit of search and have found a few other forums with people experiencing similar problems, but never have I found any real resolution. Hopefully you guys can help me get this one working, any advice would be very appreciated! I'll be sure to update with any progress.

Thanks!

kineticturtle
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Matthew Joseph Payne

I've brought a few old Casios back to life, can you post some photos of the power section of the board?

...and I'm assuming you're absolutely certain the two transistors have the same pinout... ...and that you've tried both batteries and a wall wart... smile

DipSwitch
Offline
Bucks County, PA

Yup yup yup!

I threw whatever NPN I had laying around yesterday, but went out and bought the proper darlington this morning-- still to no avail! I've tried both means of power, but neither will get it going sad

I wired a switch in place of the old one, because the contacts were a little corroded (those are the red and white wires), I thought that might be the issue... Still nothing. Also, the trace for the via on the base of the diode gave, so you'll see there's a little bridge connecting it to the next point.
Oh boy.. What a mess.

These are lame pics, but I don't have my nice camera atm... I'll take better ones tomorrow if needed!

More here

Also, completely, totally, not even remotely related, but I had some stickers of yours I put on a lighter years ago. It's still one of my favorite things ever lol!

OKAY, anyway... Thank you for the help!!

DipSwitch
Offline
Bucks County, PA

Oh! In regards to the correct pinout, and for anyone reading this in the future, typical NPN transistors for CBE-- but the board requires BCE.
You have to twist the B&C legs around to match.

The darlington I got (TIP120) came BCE in the package though, so no bending necessary!

kineticturtle
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Matthew Joseph Payne

Ha nice, thanks for sharing that! I love seeing my stickers out in the wild. smile

Can you show the other side? Also, have you tried replacing the barrel power connector? It's a switched connector so if it's effed up it can cut off both battery and external power.

DipSwitch
Offline
Bucks County, PA

Here's another album with a better camera

I've not thought about the power connector, but the multimeter is reading it properly, even when batteries are in, the correct pins are  7.5v/gnd.

Power is definitely getting to all the chips, I've traced it all over the board! Not sure where it's getting lost.

kineticturtle
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Matthew Joseph Payne

Well if you've actually traced power to the power in on the chips, that's pretty telling.

Does the power LED light? Have you tried the out jack as well as the speaker?

DipSwitch
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Bucks County, PA

No on the LED. I was able to get it on shorting a couple different combos of pins, but no sound.

The SK-10 doesn't have a headphone jack, just the speaker-- which as far as I can tell is working (wiring it up to a battery gets you the expected cracks and pops)

catskull
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NUMBSKULL

Replacing all the caps can't hurt.

kineticturtle
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Matthew Joseph Payne

^ truth