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[gmeredith]

Hi all,

Some of you might be familiar with my sample memory expansion mods for the Casio SK5, SK8, SK60 etc:

http://www.warningwillrobinson.com.au/index_files/SKexpansion.htm


These expansions typically used a Texas Instruments BQ1405y 4MBit NVRAM chip to give a 16x sample memory expansion (or BQ1406y for 32x) with sample memory retention when powered down with no batteries (have inbuilt battery with 10yr lifetime); they are a great chip.

Sadly, Texas instruments no longer make them:

http://www.ti.com/product/bq4015y.


Instead, they have provided details of an external memory retention controller chip that can be connected to any normal SRAM chip of the same size as the BQ1405y:

http://www.ti.com/product/bq2201/description

The addition of this chip to a normal SRAM chip will effectively turn it into an NVRAM chip with the addition of a 3V coin cell battery, which will retain the samples in your SK sampler even if the keyboard batteries go flat or if you only use an AC adapter and no batteries. Here is the SRAM equivalent that you would use in the 16x expansion:

http://au.element14.com/alliance-memory/as6c4008-55pcn/ic-sram-4mb-5-5v-512kx8-32pdip/dp/1562900

You don't actually need this chip as such to have non-volatile memory in the SK5/8/60 samplers - so long as you have batteries installed in the machine, it will remember the samples. But the controller chip + coin battery installation means you're not relying on the AA batteries to hold your samples - all 64 of them.

One big advantage of this change is that normal 4MBit SRAM chips are very cheap - a few dollars. Compare that to the equivalent NVRAM chip at $80 or so - if you can find them any more.

Cheers, Graham

[kloroplaster]

Thank you for these helpful guides! Please update it when you have tried with the cheaper memory if it was successful or not.

[gmeredith]

It will work, guaranteed, with the cheaper SRAM, because the RAM that is normally in the SK5/8/60 is already SRAM, just a smaller size. You would be swapping out the same type of RAM, just a bigger size.

[wax+wire]

how would doing this affect the RAM chip patchbay bends that people do?

[gmeredith]

The RAM bends should also have the same effect on the new RAM, since it is actually the same RAM as before, only with some extra address lines. Sometimes the pin functions on these larger chips are juggled around to different pins compared to the old ones, so comparing data sheets between the chips will show this.

Cheers, Graham

[Circuitbenders]

and you can get 5 of those BQ2201 controller IC's as free samples from the TI site. 

[gmeredith]

Gotta love the free stuff 

You can kind of do the same thing without the chip, just using a diode on the coin battery to prevent reverse voltage to the coin battery when the power is on. The presumption is whether there are passive components on the circuit board that might drain the battery when powered down. I guess the chip acts as an isolation latch to prevent this happening, amongst other functions.

[wax+wire]

Thank Graham,

What is the chance that a RAM chip would get fried/confused at that would be why a Casio SK5 that has no bends (or all the bends have been removed) acts up (some sounds work fine, some sounds are permanently 'bent' and some work if you ground a pin)??

I've got a Casio SK5 lying around that this happens on, and I reckon i did something to one of the RAM chips...

Or is their one chip that is preset sounds and one chip for the sampling function?  If so, I think I need to replace the chip that is the preset samples.  Is this possible/likely the issue?

either way i'm keen to fix the machine AND add extra memory.