K2000 repairs, was Re: [sdiy] Andromeda A6 hardware questions

[Scott Nordlund]

> Are there any K2000 repair experts out there?. I've got a couple of
> K2000 keyboards (Janis board) that are slowly fading away and would
> love to hear some stories/tips/spare parts sources....

I just fixed a K2VX (and a PC88 yesterday...), not that it makes me
an expert.

> Here are some common faults I've found..
> * Apparently the PSU in the keyboard version is not very reliable, and
> can fail, as it is barely adequate for a fully-loaded machine (a
> bulging electro cap is the tell-tale)
 
They cheaped out on parts.  My caps failed to the point that it would
get stuck in a crash state for several minutes until the +5 rail 
stabilized, and also the contrast voltage to the LCD was out, so the 
display was super dark.  The PSU should be ok, but an internal HD is 
probably a bad idea.  Maybe a better fan would be nice...

> * The backlight eventually goes dim on all of them. I've seen a
> repair/upgrade on the web, but it needs some trace cutting, and also
> draws more power than the original from the +5V line, so an internal
> SCSI HD on the keyboard version is now not possible with the mod, which
> is a bit of a drawback if you want user samples.
 
There's a replacement LED backlit display now for $30.  I got one but
haven't yet installed it.

> * The chassis/case on the keyboard model is made of quite brittle
> plastic, so the housings for the screws holding the two halves apart
> can fail over time. (this has happened to both of mine)
 
Yeah no kidding, mine had cracks in the case, 6 broken keyboard mounts,
one broken PCB mount, broken pitch/mod wheel mounts, and the power 
connector was broken too.  J-B Weld is a nice thing to have.

> * output transistors on the separate outputs in the rack model often
> fail. (several times on my first Rack machine)
 
They're not output transistors but there for muting when switching 
on/off.  They fail due to ESD.  Mine's got a kludge board with 1N4001
diode clamps.  I suppose you could just clip them out if you wanted.

> Also, a couple of momentary switches on one of mine have failed - the
> ENTER button + MIDI buttons sadly.... hmmm.
 
I replaced all buttons on mine.  Dunno if the rack version is different
but I had a hard time finding correct switches.  The Omron ones with 
the 3.8mm thing on top are too big, but 3.3mm is too small.  I got 3.3 
and glued them.  Installed white LEDs too while I was in there, and 
added a resistor to make them a little less blinding.

> If you do go for one, get a V3.54 or V3.87 - the latter is much faster
> with SCSI loads, but is slighty more unstable (occasionally it will do
> a hard reset on boot-up without being asked to....)
 
I have 3.54J and I'm wondering if the upgrade is worth it.  The EPROMS 
are $50 on ebay.

> Having said that, they are still great machines, with some very
> advanced modulation options for the time (controller sources can be
> processed with algebraic and other functions - the so-called FUN
> section).
 
I only just got a K2VX in January, broken, for $50.  Took a hell of a lot
of work though, and I'm not done yet...  From a modern perspective 
there's not a huge amount of stuff happening per voice, even compared to 
something like a DX7.  Most of the DSP functions seem to be limited to 
a handfull of lookup or MAC operations, which seems like a ripoff since
I've been spoiled by PD and whatnot.  But as an instrument it's great, 
very well designed all around. 		 	   		  
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