Vintage Synth Repair

thanks alot, duncan. i've already got the unit open. i'm not an EE,
but i've done a good amount of synth/electronics work over the years,
and avoid by any means necessary taking any steps that im not 100%
sure about. just a little backstory, fyi...

-my readings: PSU is putting out +15/-15. i have yet to leave it on
for a few hours to see how the voltage drifts(previous owner said phil
diagnosed a voltage drift after being on for a while.) so it is
working currently, but i want to restore it best as i can before
putting it into my studio for regular use.


-previous owner had synth looked over by phil cirocco-yes, he is
apparently one of the foremost ARP techs in america. also is
apparently MIA-i have sent him an email or two over the past few
years, no reply. common story, i believe he is moving or something.
nevertheless, previous owner was told by phil it needed a transformer
replacement, and would cost $200. transformer APPEARS to be in good
shape, but again, could be a time-delayed problem. seems a little
unlikely to be the x-former, but phil's the pro, im not. 

-as i would like to maintain the unit's health for many years to come,
i'd like to get the PSU in best shape as possible. with the power
transistors being obsolete, 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? here is a
link to the spec sheet:

http://www.power-one.com/cgi-bin/acdc_search.cgi?volts_1=15&volts_2=-15&ref=linear&x=61&y=4&LINEAR=f

the main issue i have now is measurement of current draw, as im not
sure what the + and - sides of the 2600 need. is my line of thinking
way off here? the old PSU is actually very simply laid out; there is
continuity amongst the 2 +15V output pins and the 2 -15V output pins,
as well as common, so i dont see why i couldnt tie each respective
output wire grouping together, and run directly to a new PSU. 

sorry so long here, just trying to be comprehensive. please punch any
holes in my theories if anything sounds too wacky! thanks alot,
guys-really appreciate the help. -rj

 

--- In vintagesynthrepair@yahoogroups.com, "duncan" <ferrograph@...>
wrote:
>
> >>the synth is an arp 2600. the current owner i am purchasing from had
> the synth looked over by phil cirocco, and he said the transformer is
> causing voltage drift over time, so assuming the part is reasonable,
> im gonna start with that and then see if the problem still exists.<<
> 
> this only makes sense if there is something physically wrong with the
> transformer- like corroded windings shorting out or something. in any
> case, the regulator circuits (however they are designed) downstream of
> this should either be taking care of the variations or dropping out
> entirely. these symptoms, in addition to any deterioration in the
> transformer, should & would have been picked up by any reputable synth
> tech during his "looking over" the synth. being as it's a 2600, this
> is no small matter- the thing is practically a valuable antique by
> today's market standards. I though I recognised cirocco's name as a
> reputable tech- perhaps someone else can confirm this? in any case,
> you need to get a second opinion before throwing any money at this or
> opening the thing up yourself. something sounds wrong here.
> 
> duncan (an actual engineer)
>