Casio SK-5 Bend

[rusty sheriff]

So the SK-5 has been sat around the house doing nothing ever since I bought it from a charity shop for £2.50  Werd. £2.50! I've decided it's time to try a 'planned' circuit bend on it, i.e. not just patching random cable everywhere and blowing the main IC's!

Can anyone offer any initial pointers before I break it? Interesting bends? Components I need? 1k 10k or 1m pots?

Thus far I have found out that I should head for the 24 pin IC's, and miss the corner pins (+ & -)...

Any suggestions would be greatfully received, and would result in one of those overly long hugs...

[Circuitbenders]

All the main bends are from shorts on the two big chips side by side on the left of the board (back off, face down). Most of the pins connect from one chip to the other so you only really need to work with one. Most people, including me seem to go with a patchbay in the speaker cavity but i did a custom job for someone a whole back with about 60 switches instead. That was a fun bit of wiring, oh yes indeed 

The only pot i use is a 470K (i think) for the percussion pitch. All the connections for this can be found just above in main bendable IC's with the licking yer finger and poking technique around the hole in the board in that area.

Did someone work out a filter bypass mod for the SK-5 or was that just the SK-1?

[djsynchro]

My SK-1 bypass mod was inspired by a mod (In a Yahoo SK-5 forum I think) where you take the unflitered signal from one of the legs of a transistor, but apparently it's very low output that way.

[gmeredith]

Almost all of the bends/mods for the SK-8 are applicable to the SK-5, it's very close relative.

Here is the list of mod's I've done to my SK-8:

32x sample memory expansion, 2-digit LED display for 32 sample memories, LFO pitch oscillator, pitch bend controller wheel for instrument sounds, pitch bend for drum sounds, drums direct out jack (with filter bypass), instrument direct out jack (with filter bypass), MIDI IN circuit, MIDI THRU circuit.

I'm also planning to install an Auto Power Off bypass circuit I've designed, when I get time

You can find all of these mods plus more at the Yahoo Casio SK group:

http://launch.groups.yahoo.com/group/CasioSK/

They're in the FILES section on the site (you'll need to register to access them, though)

Also, some extra ones are discussed here, including a VCF filter with resonance and CV input, an ADSR unit and others:

http://www.jz-server.de/forum2/e107_plugins/forum/forum_viewforum.php?12

and

http://www.jz-server.de/forum2/e107_plugins/forum/forum_viewforum.php?16


You can download the SK-5 service manual here:

http://www.jz-server.de/forum2/e107_plugins/forum/forum_viewforum.php?29

Below are a few pics of my SK-8 with all of these mods.

Cheers, Graham

[gmeredith]

D'oh!! Forgot the pics!

[rusty sheriff]

Muchos Gracias!

That's fantastic!

Your mod looks the bees knees, very prof looking! I especially like the labels on the case for each connector.
Thanks (kudos given) I now have a decent starting point...

[Circuitbenders]

wooah! now thats dedication.

Thats a good looking machine, nice one.

[rusty sheriff]

Ok, well after all of your input I go to task last night/this afternoon and shock horror... completed a bend! Wooo! 

This is my first, so I stuck to the basics. I'm pleased with the results which will make some appearances on the upcoming CD I feel sure!

Here's the piccies:





Again, thanks for all of your help guys!

[computer at sea]

So here's an I-think-I-broke-it-does-anyone-have-any-ideas type question.  I was poking around the two big chips on the SK-5 (and nowhere else, as far as I can recall) while running a beat.  Now the only thing that works is the rhythm side.  No input from the keyboard seems to do anything.  I discharged all the caps, and left it alone for a week, and the problem still is there. 
Does anyone, particularly Graham, have any insights?
Much aprreciated.

[computer at sea]

Update:
I guess I didn't discharge all of the caps the first time, cause I gave it another pass and brought it back to life!

[gmeredith]

That sort of thing has scared me sh**less with my SK8. A few times I really thought i'd stuffed it good, but after walking away in disgust for a few days, it suddenly started working. I've come to the conclusion that these SK keyboards are nearly bullet-proof.

However, here's a bit of a tip that will protect your machine while you're poking around - make a circuit bending test cable - a piece of insulated wire with an alligator clip on 1 end, and a multimeter probe on the other.
Now, cut the wire and solder a 10k resistor into the wire somewhere.

Now use it to test your bends. If you accidentally happen to hit a potentially damaging connection (such as shorting out the power supply rails with a chip somewhere) then the main brunt of the power is blocked by the resistor, and your circuit will stand a much better chance of surviving. 90% of all bends can still be achieved with the resistor in place. For the other ones, check the SK schematics first and identify which tracks are carrying the power, and mark them as a warning when poking around.

Cheers, Graham