[sdiy] Help calibrating Emulator II power supply... Thanks inadvance !

[Gil W.]

Hi, 

Thanks, well it happened a few months ago, ended up then by setting these two trimpots to the center position, and the E-II worked with no issues.


I tried to find the documentation needed for calibrating the PowerSupply but couldn't find anything as of yet.

What would you suggest ? do you think I can keep on using it like that ? and other "trick" I could use to make it work on the safer side ?



--- On Sat, 3/19/11, Mike Pepper <profpep at hotmail.com> wrote:

> From: Mike Pepper <profpep at hotmail.com>
> Subject: Re: [sdiy] Help calibrating Emulator II power supply... Thanks inadvance !
> To: "Gil W." <gil_we at yahoo.com>
> Cc: synth-diy at dropmix.xs4all.nl
> Date: Saturday, March 19, 2011, 5:21 PM
> > I was recapping the power supply
> in my E-II and mistakenly fiddled with
> all four trimpots on the PS circuit, trying to set the
> correct voltages. I
> found that only two of them affect the voltage rails
> (-15v/+15v/+13.2v) but
> the other two don't affect the voltage at all.
> >
> > I now have no idea how these other two trimpots
> (marked as R109 and R110
> on the schematics) should be set and am afraid that being
> set wrongly I will
> damage the E-II.
> >
> > Does any of you have any idea what they do and how
> they should be set, or
> have an access to the calibration procedure of the E-II ?
> >
> > here are the two trimpots as appearing on the
> schematics:
> > http://www.fileden.com/files/2006/10/13/285304/E-II%20PS.JPG
> 
> A few thoughts:
> 
> This is a line power switch mode, and the two pots are on
> the line side of
> the high freqency transformer. Be careful, a sort here, or
> a finger on the
> wrong bit is dangerous.
> 
> The switchmode gets it's chopping frequency from the
> Unijunction transistor
> Q101, this is used to drive chopper transistor Q103. All
> this section is
> live to the mains! It looks like R109 sets the startup
> frequency,
> independently of the feedback loop. R110, I guess, sets the
> baseline of the
> feedback from the opto in the 5V output, (A101) and the
> transformer winding
> 7--8.
> 
> You definitely need the manual, and you might need an
> isolated scope probe
> too, or a 1:1 mains isolating transformer.
> 
> My advise is to proceed with care, and not to use the Emu
> until you've
> sorted the supply. I'd do my testing with some dummy loads,
> the Emu is too
> precious to risk killing if the supply goes wrong.
> 
> There appears to be an over-voltage crowbar circuit,
> (around A103) in the
> 12V output. If this goes off, check the mains fuse, and the
> chopper
> transistor.
> 
> Hope this is of soem use.
> 
> ||\/||ike
> 
> 
> 
>