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

[Gil W.]

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
> 
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
> 


__________________________________________________
Do You Yahoo!?
Tired of spam?  Yahoo! Mail has the best spam protection around 
http://mail.yahoo.com