Vintage Synth Repair

Hi, group.

I've finally completed my System 100 by acquiring the mixer and
speakers from Australia.  Can anyone give me some guidance on
replacing the power cord/transformer to make the mixer function at
120V (from 240V)?  It would also be helpful to have the service
manuals for all the modules if anybody can recommend a source that's
reasonably priced/free!

Thanks,
Stephen

Hi!

I've got a few schematics of the System 100... but not of the mixer.
If you want me to, I'll do the calculations for your transformer. 

But if you want a more simple solution, buy a step-up converter that
will take your 120ACV 60Hz to 240ACV 50Hz. Those are easily available.
Just Google it up to find the nearest dealer.

thanks.  I thought about a converter, but I think I'd prefer to just
go ahead and wire it up.  will I likely need to replace the
transformer altogether or just wire it differently?

I appreciate the help and any schematics you could pass
along...milotoll@...

stephen 

--- In vintagesynthrepair@yahoogroups.com, "maschinengeist001"
<maschinengeist001@...> wrote:

>
> Hi!
> 
> I've got a few schematics of the System 100... but not of the mixer.
> If you want me to, I'll do the calculations for your transformer. 
> 
> But if you want a more simple solution, buy a step-up converter that
> will take your 120ACV 60Hz to 240ACV 50Hz. Those are easily available.
> Just Google it up to find the nearest dealer.
>

>>thanks.  I thought about a converter, but I think I'd prefer to just
go ahead and wire it up.  will I likely need to replace the
transformer altogether or just wire it differently?<<

stephen- don't take this the wrong way- it's meant with the greatest
of respect: is the work within the scope of what you can manage
yourself with a screwdriver & a soldering iron? then you might be able
to tell whether it's possible or not just by looking. a working
knowledge of basic linear power supplies is essential, as is a healthy
respect for household voltage, & an ELCB device.

I've done the same modification to a lot of stuff, including moog
sources.... but japanese gear tends to be awkward.

basically, in ANY electronic kit with a linear power supply, the
primary side of the transformer (the side that's attached to the
mains) will usually be a simple single coil (& therefore stuck on
whatever voltage range the boxes were targeted at when they were made)
or there'll be two or more coils, possibly connected via the fuse &/or
a voltage selector.
some of these can be pretty obstruse (e.g. yamaha cs series), but
generally you can work out what's going on with a steady eye & a
voltmeter. pen & paper optional, but advisable. :-)
 
*mandatory* if you intend to power the kit with the lid open or off,
is an ELCB.

anyway. all that said, & of immediate relevance to you, my 104 
sequencer appears at first glance to have a split primary. but the tap
isn't symmetrical, it's at 200V. I have no idea why- the tap isn't
used. is there a territory that uses 200V ac?

the two seconday coils appear to be identical & 24V ac. the 104 is
based on a tv channel selector chip, btw. 

I have a schemo somewhere.... [hunt hunt] I'm sure I found it on the
interweb originally...

I'm back. one sheet of A4 later... the tap I mentioned is on the
schemo, but not attached or annotated. the schemo says there's
different part numbers /for the whole pcb/ for 110 & 220. this is
because the 220V version has fuses mounted on it, the 110V doesn't.
otherwise, they are the same.

ok. the dc voltages are + & - 14V. there's a +23V unregulated output
from the power supply too, but I can't find where it goes, if
anywhere. it might just be a test point.

it's worth getting hold of a step-up (or down) transformer for
diagnostic purposes. first of all, you can establish that the kit
actually works at all, & then take any problems back to the guy who
sold you it! but then you can measure the on-load & off-load voltages
at the secondary side of the mains transformer & use this data to
source a suitable replacement from radio shack or wherever. I usually
look for a toroidal, because they're quieter, but they can be quite
expensive. 
use the label on the case of the kit as a guide to the size you'll
need: my scruffy old 104 says 5W, so I'd be looking for a toroidal
somewhere around 10VA, the smallest ones I've seen. it could be that
you'd need to go up a size or two to get the right secondary voltages. 

these low AC voltages need to be in the right sort of range for the
device to work well. it's more obvious with more modern kit where you
can clearly see 78xx & 79xx series regulators; roland seemed to prefer
to build their own regulation, but as a rule of thumb (& assuming you
have the wherewithal to measure them), the AC secondary voltages need
to be about the same as the regulated DC voltages required inside the
kit. this is on-load.
to get technical- after rectification & smoothing, the rms voltage
from the secondary becomes an unregulated dc voltage about 1.4x as
high. but there is a loss of voltage ("diode drop" & operating
headroom) through the series regulator which smooths this voltage for
use by the audio circuits. 
swings & roundabouts, we call it in the UK. 

so (sticking with roland but changing series), I had to replace a 110V
transformer in an sh2000 to run it in the UK. the regulated DC
voltages are (IIRC) + & - 15 V. 
so I needed a toroidal- 
with two secondary coils of 15V ac each, 
the whole thing rated at 20VA, 
that could physically fit in the synth.

it worked, while a 20VA toroidal with 12V ac secondaries did not.
didn't do any harm to try it, but the synth sounded horrible. 

the last point (size) is not an insignificant consideration, but
usually things work out ok.

so, for the 104, you need a small transformer (10VA-ish) that will fit
in the case where the present one is, that has two secondaries of 24V
ac. actually, this is generous for a result of 14V after regulation,
but it's what roland thought was necessary. it would probably work
with secondaries of 15V ac.... certainly 18V ac would work.
 
the two secondaries go in these pairs: red & black are one coil,
yellow & grey are the other.

I don't imagine the other system 100 components will differ wildly
from this approach, but they might....

hope this helps!

duncan.