Sequential circuits samplers

<< I don't think it would have been for system checks anyway, more likely it 
was for adjusting the analogue circuitry, i.e. a bunch of waveforms, with the 
patches set up to check open and closed filters and amps, crosstalk, the mod 
depth of the lfo and stuff like that. >>

oops. not quite right.... I got my schemos today; turns out to be the whole 
maintenance procedure aswell as the diagrams, so if anyone fancies making 
their own memory expansion board..... all the details are available.

anyway, this fabled diagnostics disk (sic) was part number 879 and, once 
auto-loaded, would test the following:

counter/timer/register
keyboard
output filter
dac (3 tests)
sound ram
led's
switches
footswitches (though, bizarrely, all the tests require the use of the aux 
footswitch anyway.)

so I was nearly right. the disc is useless if the cpu doesn't load it in the 
first place, with the first lot of tests being applied to the data busses in 
and out of the system and sound memory; the diagnostics do run the machine 
instead of the normal eprom though. 

the cpu runs at 8Mhz, divided down from a 16Mhz crystal, while later models 
(later than what, it doesn't say) or any that went for servicing, have an 
additional 6Mhz clock circuit (an extra board sitting where u218 should be on 
board 2, some revA's and all revB's) for the audio circuits, "vital for 
proper operation" apparently.  I've seen this in at least one of my machines 
and wondered what the hell it was... if it's been done in the field, as would 
be the case with a few european machines, I would imagine that there could be 
problems here.
these sheets describe how to perform this and all other field mods- there are 
quite a few, including one (eek!) that changes the sound of the filters... 
makes them brighter..... also potential for the guys at the shop to mess up.
(no offence, anyone from TSC that's reading, but you guys are shit at 
soldering).

disappointingly, the manual only mentions the disc drive in passing, to say 
that the original unexpanded boxes were fitted with a single-sided drive, 
part number md351 (on the underside of the drive, apparently, though I doubt 
many of these original drives have survived). this changes to md350 for 
double-sided, and some track has to be cut on board 2 if this is a retrofit. 
doesn't mention the make at all. it's implied that the DD drive would have 
been standard on unexpanded machines after a certain point anyway. floppy 
action is through u210 and u205, which might be worth examining if a known 
suitable drive fails; 201 is a 7406 (inverters) while 205 is a wd1770. it's 
basically a de/serializer but I wouldn't want to try replacing it with 
anything else- my logic skills aren't up to it.

there are quite a few proprietary chips in there, including the kybd 
controller :-( and a few other chips that were off-the-peg at the time but 
might be hard to find now- the 12-bit successive-approx register on the 
sample input, for instance. 

the vca/vcf chips are curtis 3379's, probably as rare as rocking-horse-shit 
now. voice one has a 440Hz input for tuning samples to (echoes of minimoog 
here) while all the voice chips have an unused pan cv input. 
how frustrating is that? 
there really are two more vca's in each voice-chip, set up to pan a common 
input to one or the other output in response to a cv. instead, output comes 
from an earlier stage, mono-only. the first four voices are hard-wired to the 
left output and the other four to the right..... I'm toying with the idea of 
a mod now.... 
and if I really can't revive my 2000, then these curtis chips might form the 
basis of a couple of rackmount monosynths one day. everything is analogue 
volt-controlled on them; fabulous. there's a separate sheet in amongst the 
schemos showing how to hook up one of these 3379's to full advantage; just 
add oscillators and eg's. 4-pole, they are. I'm sure this is doug curtis' own 
writing on here- I've got a similar sheet on a cem chip in the cheetah ms6 
service sheets.....

anyway.

I'll be sending copies of this manual and the op manual to ben (good lad) to 
publish to the list.

duncan/radio massacre international/london