I am looking for a Sanchez keyboard manual ark 2188 or a similar manual to learn to play a keyboard

Seems to be a little known South African keyboard. Some manuals but not yours.

https://www.google.com/search?safe=off&rlz=1C1QJDB_enCA643CA644&sxsrf=ALeKk016am5sk2l8qqEQHKV8SQsEs8ZO_Q%3A1615762755259&ei=Q5VOYLqcD5CIggfDurroBQ&q=Sanchez+Ark15+manual

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Yamaha has the Owner's Manual for the PSR-290 portable keyboard on the product page: http://usa.yamaha.com/products/musical-instruments/keyboards/digitalkeyboards/portable_keyboards/psr-290/ . Click on the Support tab and look the Downloads heading. If you want the English version of the manual, just click on the second link. If you would like the manual in another language, click on the More Downloads link.

The current link to the English version of the manual is http://download.yamaha.com/api/asset/file/?language=en&site=usa.yamaha.com&asset_id=2381 . This is a PDF so you will need Adobe Reader DC or a similar program.

I hope this helps.

Cindy Wells

http://www.novationmusic.com/support/downloads/

They do not list the MK 928 as such, but that does not mean it is not listed by another name.

Failing that, there are a fair number of keyboards with other manufacturers names on them that came from the same chinese factory, they would all follow the same sets of commands and instructions so a manual for a keyboard similar to yours with a different name from Novation, or if you were to find another 928 sith a different name on it- if it looks the same, with maybe different colored plastic, but laid the same with the same features- it is the same.

http://support.casio.com/manuallist.php?rgn=1&cid=008
The link i have attached is a direct to Casio's website and their user manuals. i dont think the one your looking for is on the however, you might find a model very similar to yours to use as a reference.
is there a problem your having with the keyboard?

Each key has two contacts. One closes first and then the other. This allows the processor to measure the key velocity which is then used to control volume. The key contacts are conductive rubber "pills" pressed onto circuit board traces. Clean them ONLY with 99% isoprophyl alcohol and Q tips. The disassembly of the unit to access these is NOT for the inexperienced so you might want to take it to a repir shop. Here is a service manual for a Casio 811 which is totally different packaging than yours, HOWEVER the keyboard itself will be similar and you will get an idea what is involved with getting into one of these things:

http://elektrotanya.com/casio_ctk_811_ex.pdf/download.html

Scroll down to "get manual" and click to download... IGNORE other download links.
The keyboard exploded view is around page 32 in this manual.

Is it possible you have the wrong power adapter? Next to the power socket on the back of the keyboard it should say what voltage and how many milliamps it needs (eg: 9v DC 500 mA). You should find a similar rating on your adapter.

If the adapter doesn't quite produce enough mA the keyboard will happily sit doing nothing but shut off when you raise its power requirements by playing a lot of notes.

Read your manual regarding "fingered chords" and similar subjects. It sounds like you are in a single fingered chord mode...

Try the organforum . com. There are a lot of Hammond people there. The model 700 is the base model and probably enough to get you started.
Also just get a organ music book as a lot of the vernacular is in those. Also check your library for organ books. OFTEN the user manuals aren't much use to learn the instrument.

Most organs will either have tabs or drawbars. These select the type of "voice" and often one selects more than one as a mix. Each keyboard is refered to as a "Manual". Most organs have foot pedals. Each of the manuals and the foot pedals will have a seperate set of tabs associated with them.

To get started, turn on the organ and press the expression pedal which controls the volume... experiment setting a few tabs or drawbars an play notes on the manuals. You will soon learn what controls what.

Note that some models of Hammond organs used rotating tone wheels and those require lubrication. Those that do, usually have a power switch labelled "start" and "Run". These organs are usually higher value and one should have them serviced before using.

Since I don't know where you are I'm sending this link:http://www.casio-intl.com/emi/piano/privia/px310.html Here you will find info on their past and present keyboards, support information and manuals. I hope this helps you.

http://support.casio.com/pdf/008/CTK4000_5000_e.pdf
Here it is...