Vintage Synth Repair

>>previous owner was told by phil it needed a transformer
> replacement, and would cost $200.<<

$200 for a transformer?? a tad excessive, even with the price of
copper being what it is... besides, as we have said earlier, if you're
getting good 15V rails most of the time & the thing doesn't look or
smell bad, it's more likely to be something in the regulation that's
going bad. check for bad solder joints, especially around the large
power components- the rectifier diodes & the pass-transistors.
see the posts about the juno 106? same thing, more or less.

yes, & let the thing drone for a few hours (2600s are supposed to be
good at this!) into a guitar tuner, see if it drifts any. of course,
this could all be component breakdown elsewhere in the thing & nothing
whatever to do with the power supply. 

e.g. I had a korg monopoly that would not stay in tune- this turned
out to be the way the thermistors were glued to the oscillator chips;
the glue went bad & the thing started drifting. the 2600 is full of
such design quirks, as I recall. mostly in epoxy-potted blocks, right?
:-/ 

>>i am now considering another approach:
> drop an entirely new, linear power-one PSU in as a replacement. the
> 1.5A unit is only $72, which is relatively very cheap. puts out
> +/-15V. i have used power-one linear units several times before on
> other projects, and have always found them to be rock solid, easy to
> calibrate, and good build quality. is this a horrible idea?<<

not really so horrible, & it would mean you could use the arp off any
line voltage/frequency. but it wouldn't be stock any more, & that
would affect resale value. personally, I don't care about such things-
to me it just indicates that someone did some restorative work so that
the instrument had a longer active life. I hate this "museum-grade"
nonsense... :-)  

but maybe you can measure the current draw on the existing power
supply first. 
the first "gotcha" is likely to be the -15V which, from many
commercial computer grade SMPSU modules is likely to be capable of
only a few hundred mA, compared to a couple of amps at 5V or 15V
positive. your average analogue synth has more or less symmetrical
current draw....
 
the second is going to be radiated HF noise from the power supply. put
it in a faraday cage (you may have seen this approach inside, say, an
emu sampler) & fit ferrite rings on the output cables.

third, it may just affect the sound a little bit... depends how
"golden-eared" you are, but you'd be replacing an analogue power
supply with a digital one & this will to a small degree affect the
behaviour of the synth, sonically.

let us know how you get on- that's what this list is for! :-)

duncan.