[sdiy] Prophet 5 -15v rail is shorting... Need advice

[Gil W.]

Wow... Now I realize I'm also using 1N4007 which are
1A !! So definately I used wrong parts ! But could
this cause the exact +15v problem I mentioned ?

Thanks again !




--- "Gil W." <gil_we at yahoo.com> wrote:

> How about this ? (see attachment)
> 
> I'm using a 2W08 diode bridge as a rectifier.
> The datasheet shows max. 2A while the circuit needs 
> a 2.8A transformer ? am I using the wrong type of
> bridge ?... or am I referring to the wrong parameter
> ?
> 
> 
> Thanks all !
> 
> 
> --- ASSI <Stromeko at compuserve.de> wrote:
> 
> > On Donnerstag 08 November 2007, Gil W. wrote:
> > > Could it be that the transfomer used it not 100%
> > > suitable for the P5 applications, therefore I
> both
> > get
> > > fried tantalums on the -15v rail, and lack of
> > voltage
> > > stability on the +15v rail ?
> > 
> > If the specs for the transformer you've given
> > earlier are correct, the 
> > transformer should be adequate.  You can however
> > check if the voltage 
> > directly at the secondary windings and after
> > rectification is 
> > reasonably stable (under constant load and with
> load
> > variations).  
> > Depending on the type of regulator you're using,
> you
> > need a minimum 
> > voltage of at least 18V into the regulators. 
> Since
> > the positive side 
> > feeds both the +15 and +5V regulators, it has more
> > load to cope with.
> > 
> > As someone else has already mentioned, the ground
> > layout for the power 
> > supply requires some consideration.  You do need a
> > proper star layout 
> > to ensure that the reference path for one
> regulator
> > is undisturbed by 
> > load variations in the other.  I would add that
> the
> > bypass caps in 
> > front of the regulator need to be as close as
> > possible to the same.  
> > This rule should also be followed for the filter
> > caps after the 
> > regulator.  I also hope you have not missed that
> > D506 diode in front of 
> > the +15V regulator bypass cap: it is absolutely
> > necessary to have it 
> > when you have a second bypass cap for the 5.6V
> rail!
> > (I would rather 
> > put it in front of the 5.6V regulator or use a
> > second rectifier bridge 
> > to decouple the two bypass caps, but that's
> another
> > story).  This part 
> > of the schematics is a bit funny, it appears that
> > the +15V rail was 
> > added after the rest of the circuit was already
> > designed and then later 
> > the 12V and -5V rails were removed (if your
> Prophet
> > has 2708 EPROM it 
> > still needs those voltages, if it has 2732 ones it
> > doesn't).
> > 
> > 
> > 
> > Achim.
> > -- 
> > +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb
> > Andromeda XTk]>+
> > 
> > Factory and User Sound Singles for Waldorf Q,
> microQ
> > and rackAttack:
> >
>
http://Synth.Stromeko.net/Downloads.html#WaldorfSounds
> > 
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> >
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> > 
> 
> 
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