Vintage Synth Repair

Powering my OBXa up immediately blows up the tantalum capacitor placed 
between the IN and GND legs of the -15v 7915 regulator... I also found 
two partially fried 1ohm fuse resistor on the +15v rail. Any idea what 
can cause it ? Is there any chance that the transformer is bad ? What 
is your bet as for the responsbile part ?

I uploaded the diagram to the Files section.... any help would be 
appreciated !

Thanks.

>Powering my OBXa up immediately blows up the tantalum capacitor placed
>between the IN and GND legs of the -15v 7915 regulator... I also found
>two partially fried 1ohm fuse resistor on the +15v rail. Any idea what
>can cause it ? Is there any chance that the transformer is bad ? What
>is your bet as for the responsbile part ?
>
>I uploaded the diagram to the Files section.... any help would be
>appreciated !

Tantalum capacitors are particularly sensitive to overvoltage (and tend to 
fail in a rather spectacular way).  Obviously you need to test what voltage 
is at that point.  Disconnect the power supply from the synth to avoid 
causing damage.  78xx/79xx regulators need at least about 2 volts of 
overhead to operate properly, and the LM723 needs at least 3, so the input 
needs to be at least 18 V.  Specifically, the voltage doesn't really matter 
(as long as it doesn't exceed the rated voltage of any of the components), 
but it determines how much power will be dissipated as heat, so a very high 
voltage is more indicative of a fault condition.

The 1 ohm resistors may have failed for a different reason.  Their purpose 
in the circuit is to tell the regulator chip (LM723) how much current is 
being drawn, and establish a maximum limit.  Obviously there was too much 
current.  A short-circuit on the output shouldn't blow the resistors, it 
would just cause the regulator to limit the current.  This leads me to 
suspect that maybe the transistor failed, or the regulator.

The transformer may have a shorted primary winding that caused the secondary 
voltages to go too high.  In that  case, ALL of the secondary voltages are 
too high, but maybe the +/- 15 V parts of the supply were the most 
sensitive.

_________________________________________________________________
The average US Credit Score is 675. The cost to see yours: $0 by Experian. 
http://www.freecreditreport.com/pm/default.aspx?sc=660600&bcd=EMAILFOOTERAVERAGE

I don't know so much about OBXa  just, obiously, that is a great synth. But
I'm agree with Scott. Another possibility is a wrong connection from primary
winding. Maybe a transformer configurated in diferent country as must be?
Regards.

Joan M.

  -----Mensaje original-----
  De: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com]En nombre de Scott Nordlund
  Enviado el: lunes, 26 de marzo de 2007 17:54
  Para: vintagesynthrepair@yahoogroups.com
  Asunto:RE: [vintagesynthrepair] Power Suppy problem




  >Powering my OBXa up immediately blows up the tantalum capacitor placed
  >between the IN and GND legs of the -15v 7915 regulator... I also found
  >two partially fried 1ohm fuse resistor on the +15v rail. Any idea what
  >can cause it ? Is there any chance that the transformer is bad ? What
  >is your bet as for the responsbile part ?
  >
  >I uploaded the diagram to the Files section.... any help would be
  >appreciated !

  Tantalum capacitors are particularly sensitive to overvoltage (and tend to
  fail in a rather spectacular way). Obviously you need to test what voltage
  is at that point. Disconnect the power supply from the synth to avoid
  causing damage. 78xx/79xx regulators need at least about 2 volts of
  overhead to operate properly, and the LM723 needs at least 3, so the input
  needs to be at least 18 V. Specifically, the voltage doesn't really matter
  (as long as it doesn't exceed the rated voltage of any of the components),
  but it determines how much power will be dissipated as heat, so a very
high
  voltage is more indicative of a fault condition.

  The 1 ohm resistors may have failed for a different reason. Their purpose
  in the circuit is to tell the regulator chip (LM723) how much current is
  being drawn, and establish a maximum limit. Obviously there was too much
  current. A short-circuit on the output shouldn't blow the resistors, it
  would just cause the regulator to limit the current. This leads me to
  suspect that maybe the transistor failed, or the regulator.

  The transformer may have a shorted primary winding that caused the
secondary
  voltages to go too high. In that case, ALL of the secondary voltages are
  too high, but maybe the +/- 15 V parts of the supply were the most
  sensitive.

  __________________________________________________________
  The average US Credit Score is 675. The cost to see yours: $0 by Experian.

http://www.freecreditreport.com/pm/default.aspx?sc=660600&bcd=EMAILFOOTERAVE
RAGE



  
  --------------------------------------------------------------------------
-------------------------
  Panda Antivirus + Firewall 2007 ha detectado que este mensaje puede estar
falseado.

  Te recomendamos la maxima precaucisn ya que los mensajes falseados pueden
indicar la existencia de un intento de estafa.
  --------------------------------------------------------------------------
-------------------------

Thanks guys !

News - I replaced the tantalum cap with one that can handle up to 25v 
and disconnected the other boards from the synth, the cap has not got 
fried at all, but voltages are inaccurate-

-15v read -14.6
+5v  read +4.25

the +15v and -5v are adjustable so they're ok...

What could cause the inaccurate voltages ? should I replace the 7915
and 7805 ? or maybe some particular caps ? or do they appear like 
this because no board is connected to the PS ?


Also, does this indicate that some other board shorts the -15v rail ?

Thanks again !!!






--- In vintagesynthrepair@yahoogroups.com, Joan Martinez 
<piniflopa@...> wrote:
>
> I don't know so much about OBXa  just, obiously, that is a great 
synth. But
> I'm agree with Scott. Another possibility is a wrong connection 
from primary
> winding. Maybe a transformer configurated in diferent country as 
must be?
> Regards.
> 
> Joan M.
> 
>   -----Mensaje original-----
>   De: vintagesynthrepair@yahoogroups.com
> [mailto:vintagesynthrepair@yahoogroups.com]En nombre de Scott 
Nordlund
>   Enviado el: lunes, 26 de marzo de 2007 17:54
>   Para: vintagesynthrepair@yahoogroups.com
>   Asunto:RE: [vintagesynthrepair] Power Suppy problem
> 
> 
> 
> 
>   >Powering my OBXa up immediately blows up the tantalum capacitor 
placed
>   >between the IN and GND legs of the -15v 7915 regulator... I also 
found
>   >two partially fried 1ohm fuse resistor on the +15v rail. Any 
idea what
>   >can cause it ? Is there any chance that the transformer is bad ? 
What
>   >is your bet as for the responsbile part ?
>   >
>   >I uploaded the diagram to the Files section.... any help would be
>   >appreciated !
> 
>   Tantalum capacitors are particularly sensitive to overvoltage 
(and tend to
>   fail in a rather spectacular way). Obviously you need to test 
what voltage
>   is at that point. Disconnect the power supply from the synth to 
avoid
>   causing damage. 78xx/79xx regulators need at least about 2 volts 
of
>   overhead to operate properly, and the LM723 needs at least 3, so 
the input
>   needs to be at least 18 V. Specifically, the voltage doesn't 
really matter
>   (as long as it doesn't exceed the rated voltage of any of the 
components),
>   but it determines how much power will be dissipated as heat, so a 
very
> high
>   voltage is more indicative of a fault condition.
> 
>   The 1 ohm resistors may have failed for a different reason. Their 
purpose
>   in the circuit is to tell the regulator chip (LM723) how much 
current is
>   being drawn, and establish a maximum limit. Obviously there was 
too much
>   current. A short-circuit on the output shouldn't blow the 
resistors, it
>   would just cause the regulator to limit the current. This leads 
me to
>   suspect that maybe the transistor failed, or the regulator.
> 
>   The transformer may have a shorted primary winding that caused the
> secondary
>   voltages to go too high. In that case, ALL of the secondary 
voltages are
>   too high, but maybe the +/- 15 V parts of the supply were the most
>   sensitive.
> 
>   __________________________________________________________
>   The average US Credit Score is 675. The cost to see yours: $0 by 
Experian.
> 
> http://www.freecreditreport.com/pm/default.aspx?
sc=660600&bcd=EMAILFOOTERAVE
> RAGE
> 
> 
> 
>   
>   ------------------------------------------------------------------
--------
> -------------------------
>   Panda Antivirus + Firewall 2007 ha detectado que este mensaje 
puede estar
> falseado.
> 
>   Te recomendamos la maxima precaucisn ya que los mensajes 
falseados pueden
> indicar la existencia de un intento de estafa.
>   ------------------------------------------------------------------
--------
> -------------------------
>

Have you replaced to 5V bridge rectifier with one of higher amp
rating? The original W02Ms used in OBs were to wimpy...

--- In vintagesynthrepair@yahoogroups.com, "gil_we" <gil_we@...> wrote:

>
> Thanks guys !
> 
> News - I replaced the tantalum cap with one that can handle up to 25v 
> and disconnected the other boards from the synth, the cap has not got 
> fried at all, but voltages are inaccurate-
> 
> -15v read -14.6
> +5v  read +4.25
> 
> the +15v and -5v are adjustable so they're ok...
> 
> What could cause the inaccurate voltages ? should I replace the 7915
> and 7805 ? or maybe some particular caps ? or do they appear like 
> this because no board is connected to the PS ?
> 
> 
> Also, does this indicate that some other board shorts the -15v rail ?
> 
> Thanks again !!!
> 
> 
> 
> 
> 
> 
> --- In vintagesynthrepair@yahoogroups.com, Joan Martinez 
> <piniflopa@> wrote:
> >
> > I don't know so much about OBXa  just, obiously, that is a great 
> synth. But
> > I'm agree with Scott. Another possibility is a wrong connection 
> from primary
> > winding. Maybe a transformer configurated in diferent country as 
> must be?
> > Regards.
> > 
> > Joan M.
> > 
> >   -----Mensaje original-----
> >   De: vintagesynthrepair@yahoogroups.com
> > [mailto:vintagesynthrepair@yahoogroups.com]En nombre de Scott 
> Nordlund
> >   Enviado el: lunes, 26 de marzo de 2007 17:54
> >   Para: vintagesynthrepair@yahoogroups.com
> >   Asunto:RE: [vintagesynthrepair] Power Suppy problem
> > 
> > 
> > 
> > 
> >   >Powering my OBXa up immediately blows up the tantalum capacitor 
> placed
> >   >between the IN and GND legs of the -15v 7915 regulator... I also 
> found
> >   >two partially fried 1ohm fuse resistor on the +15v rail. Any 
> idea what
> >   >can cause it ? Is there any chance that the transformer is bad ? 
> What
> >   >is your bet as for the responsbile part ?
> >   >
> >   >I uploaded the diagram to the Files section.... any help would be
> >   >appreciated !
> > 
> >   Tantalum capacitors are particularly sensitive to overvoltage 
> (and tend to
> >   fail in a rather spectacular way). Obviously you need to test 
> what voltage
> >   is at that point. Disconnect the power supply from the synth to 
> avoid
> >   causing damage. 78xx/79xx regulators need at least about 2 volts 
> of
> >   overhead to operate properly, and the LM723 needs at least 3, so 
> the input
> >   needs to be at least 18 V. Specifically, the voltage doesn't 
> really matter
> >   (as long as it doesn't exceed the rated voltage of any of the 
> components),
> >   but it determines how much power will be dissipated as heat, so a 
> very
> > high
> >   voltage is more indicative of a fault condition.
> > 
> >   The 1 ohm resistors may have failed for a different reason. Their 
> purpose
> >   in the circuit is to tell the regulator chip (LM723) how much 
> current is
> >   being drawn, and establish a maximum limit. Obviously there was 
> too much
> >   current. A short-circuit on the output shouldn't blow the 
> resistors, it
> >   would just cause the regulator to limit the current. This leads 
> me to
> >   suspect that maybe the transistor failed, or the regulator.
> > 
> >   The transformer may have a shorted primary winding that caused the
> > secondary
> >   voltages to go too high. In that case, ALL of the secondary 
> voltages are
> >   too high, but maybe the +/- 15 V parts of the supply were the most
> >   sensitive.
> > 
> >   __________________________________________________________
> >   The average US Credit Score is 675. The cost to see yours: $0 by 
> Experian.
> > 
> > http://www.freecreditreport.com/pm/default.aspx?
> sc=660600&bcd=EMAILFOOTERAVE
> > RAGE
> > 
> > 
> > 
> >   
> >   ------------------------------------------------------------------
> --------
> > -------------------------
> >   Panda Antivirus + Firewall 2007 ha detectado que este mensaje 
> puede estar
> > falseado.
> > 
> >   Te recomendamos la maxima precaucisn ya que los mensajes 
> falseados pueden
> > indicar la existencia de un intento de estafa.
> >   ------------------------------------------------------------------
> --------
> > -------------------------
> >
>

>News - I replaced the tantalum cap with one that can handle up to 25v
>and disconnected the other boards from the synth, the cap has not got
>fried at all, but voltages are inaccurate-

This doesn't necessarily mean the problem is entirely fixed unless you 
verify that the transformer secondary voltages are okay.  If they're putting 
out more than they should, you may overheat a regulator once a load is 
connected.


>-15v read -14.6
>+5v  read +4.25
>
>the +15v and -5v are adjustable so they're ok...
>
>What could cause the inaccurate voltages ? should I replace the 7915
>and 7805 ? or maybe some particular caps ? or do they appear like
>this because no board is connected to the PS ?

These regulators should work regardless of load.  If the input voltages are 
okay then you may want to replace them.

>Also, does this indicate that some other board shorts the -15v rail ?

not really, no

_________________________________________________________________
5.5%* 30 year fixed mortgage rate. Good credit refinance. Up to 5 free 
quotes - *Terms 
https://www2.nextag.com/goto.jsp?product=100000035&url=%2fst.jsp&tm=y&search=mortgage_text_links_88_h2a5d&s=4056&p=5117&disc=y&vers=910

--- In vintagesynthrepair@yahoogroups.com, "Scott Nordlund"
<gsn10@...> wrote:
>
> >News - I replaced the tantalum cap with one that can handle up to 25v
> >and disconnected the other boards from the synth, the cap has not got
> >fried at all, but voltages are inaccurate-
> 
> This doesn't necessarily mean the problem is entirely fixed unless you 
> verify that the transformer secondary voltages are okay.  If they're
putting 
> out more than they should, you may overheat a regulator once a load is 
> connected.
> 
> 
> >-15v read -14.6
> >+5v  read +4.25
> >
> >the +15v and -5v are adjustable so they're ok...
> >
> >What could cause the inaccurate voltages ? should I replace the 7915
> >and 7805 ? or maybe some particular caps ? or do they appear like
> >this because no board is connected to the PS ?
> 
> These regulators should work regardless of load.  If the input
voltages are 
> okay then you may want to replace them.
> 
> >Also, does this indicate that some other board shorts the -15v rail ?
> 
> not really, no
> 

Just a quick sense check - if all the voltages are reading low, and
the regulators are standard fixed voltage types - I'd have thought it
unlikely they are both in need of replacement - are you sure the meter
is reading correct? and check the ground reference point you are using?

Thanks a lot !

> >Also, does this indicate that some other board shorts the -15v 
rail ?
> 
> not really, no

What I mean is, does the tantalum cap get fried because there is a 
short between the -15v and ground caused at one of the boards, or the 
only possible reason is high secondary transformer voltages which 
overheat the 7915 regulator ?

How do I check the secondary voltages and what should I see there ?...

Thanks again for the help !!!




--- In vintagesynthrepair@yahoogroups.com, "Scott Nordlund" 
<gsn10@...> wrote:
>
> >News - I replaced the tantalum cap with one that can handle up to 
25v
> >and disconnected the other boards from the synth, the cap has not 
got
> >fried at all, but voltages are inaccurate-
> 
> This doesn't necessarily mean the problem is entirely fixed unless 
you 
> verify that the transformer secondary voltages are okay.  If 
they're putting 
> out more than they should, you may overheat a regulator once a load 
is 
> connected.
> 
> 
> >-15v read -14.6
> >+5v  read +4.25
> >
> >the +15v and -5v are adjustable so they're ok...
> >
> >What could cause the inaccurate voltages ? should I replace the 
7915
> >and 7805 ? or maybe some particular caps ? or do they appear like
> >this because no board is connected to the PS ?
> 
> These regulators should work regardless of load.  If the input 
voltages are 
> okay then you may want to replace them.
> 
> >Also, does this indicate that some other board shorts the -15v 
rail ?
> 
> not really, no
> 
> _________________________________________________________________
> 5.5%* 30 year fixed mortgage rate. Good credit refinance. Up to 5 
free 
> quotes - *Terms 
> https://www2.nextag.com/goto.jsp?product=100000035&url=%
2fst.jsp&tm=y&search=mortgage_text_links_88_h2a5d&s=4056&p=5117&disc=y
&vers=910
>

Thanks, I'm going to replace all W02M with W04 (is the ok?...)
Will also replace the regulators and electrolytic caps, and report 
results.




--- In vintagesynthrepair@yahoogroups.com, "synthparts" 
<synthparts@...> wrote:
>
> Have you replaced to 5V bridge rectifier with one of higher amp
> rating? The original W02Ms used in OBs were to wimpy...
> 
> --- In vintagesynthrepair@yahoogroups.com, "gil_we" <gil_we@> wrote:
> >
> > Thanks guys !
> > 
> > News - I replaced the tantalum cap with one that can handle up to 
25v 
> > and disconnected the other boards from the synth, the cap has not 
got 
> > fried at all, but voltages are inaccurate-
> > 
> > -15v read -14.6
> > +5v  read +4.25
> > 
> > the +15v and -5v are adjustable so they're ok...
> > 
> > What could cause the inaccurate voltages ? should I replace the 
7915
> > and 7805 ? or maybe some particular caps ? or do they appear like 
> > this because no board is connected to the PS ?
> > 
> > 
> > Also, does this indicate that some other board shorts the -15v 
rail ?
> > 
> > Thanks again !!!
> > 
> > 
> > 
> > 
> > 
> > 
> > --- In vintagesynthrepair@yahoogroups.com, Joan Martinez 
> > <piniflopa@> wrote:
> > >
> > > I don't know so much about OBXa  just, obiously, that is a 
great 
> > synth. But
> > > I'm agree with Scott. Another possibility is a wrong connection 
> > from primary
> > > winding. Maybe a transformer configurated in diferent country 
as 
> > must be?
> > > Regards.
> > > 
> > > Joan M.
> > > 
> > >   -----Mensaje original-----
> > >   De: vintagesynthrepair@yahoogroups.com
> > > [mailto:vintagesynthrepair@yahoogroups.com]En nombre de Scott 
> > Nordlund
> > >   Enviado el: lunes, 26 de marzo de 2007 17:54
> > >   Para: vintagesynthrepair@yahoogroups.com
> > >   Asunto:RE: [vintagesynthrepair] Power Suppy problem
> > > 
> > > 
> > > 
> > > 
> > >   >Powering my OBXa up immediately blows up the tantalum 
capacitor 
> > placed
> > >   >between the IN and GND legs of the -15v 7915 regulator... I 
also 
> > found
> > >   >two partially fried 1ohm fuse resistor on the +15v rail. Any 
> > idea what
> > >   >can cause it ? Is there any chance that the transformer is 
bad ? 
> > What
> > >   >is your bet as for the responsbile part ?
> > >   >
> > >   >I uploaded the diagram to the Files section.... any help 
would be
> > >   >appreciated !
> > > 
> > >   Tantalum capacitors are particularly sensitive to overvoltage 
> > (and tend to
> > >   fail in a rather spectacular way). Obviously you need to test 
> > what voltage
> > >   is at that point. Disconnect the power supply from the synth 
to 
> > avoid
> > >   causing damage. 78xx/79xx regulators need at least about 2 
volts 
> > of
> > >   overhead to operate properly, and the LM723 needs at least 3, 
so 
> > the input
> > >   needs to be at least 18 V. Specifically, the voltage doesn't 
> > really matter
> > >   (as long as it doesn't exceed the rated voltage of any of the 
> > components),
> > >   but it determines how much power will be dissipated as heat, 
so a 
> > very
> > > high
> > >   voltage is more indicative of a fault condition.
> > > 
> > >   The 1 ohm resistors may have failed for a different reason. 
Their 
> > purpose
> > >   in the circuit is to tell the regulator chip (LM723) how much 
> > current is
> > >   being drawn, and establish a maximum limit. Obviously there 
was 
> > too much
> > >   current. A short-circuit on the output shouldn't blow the 
> > resistors, it
> > >   would just cause the regulator to limit the current. This 
leads 
> > me to
> > >   suspect that maybe the transistor failed, or the regulator.
> > > 
> > >   The transformer may have a shorted primary winding that 
caused the
> > > secondary
> > >   voltages to go too high. In that case, ALL of the secondary 
> > voltages are
> > >   too high, but maybe the +/- 15 V parts of the supply were the 
most
> > >   sensitive.
> > > 
> > >   __________________________________________________________
> > >   The average US Credit Score is 675. The cost to see yours: $0 
by 
> > Experian.
> > > 
> > > http://www.freecreditreport.com/pm/default.aspx?
> > sc=660600&bcd=EMAILFOOTERAVE
> > > RAGE
> > > 
> > > 
> > > 
> > >   
> > >   --------------------------------------------------------------
----
> > --------
> > > -------------------------
> > >   Panda Antivirus + Firewall 2007 ha detectado que este mensaje 
> > puede estar
> > > falseado.
> > > 
> > >   Te recomendamos la maxima precaucisn ya que los mensajes 
> > falseados pueden
> > > indicar la existencia de un intento de estafa.
> > >   --------------------------------------------------------------
----

> > --------
> > > -------------------------
> > >
> >
>

>What I mean is, does the tantalum cap get fried because there is a
>short between the -15v and ground caused at one of the boards, or the
>only possible reason is high secondary transformer voltages which
>overheat the 7915 regulator ?

Short answer: Neither.  The cap fried most likely because there was too much 
voltage applied to it (transformer secondary is too high, excessive mains 
voltage, whatever).  If this is in excess of the rated voltage, it will 
fail, it's got nothing to do with the regulator or the load on the supply.

Longer answer: It might be possible that, given excessive current drain and 
leaky filter capacitors, there was a lot of voltage ripple at that point and 
thus the capacitor was placed under undue strain which made it more 
succeptible to failure.  But I really don't buy that, it's much less likely.

>How do I check the secondary voltages and what should I see there ?...

You'll need an AC RMS voltmeter to directly measure the secondary voltage.  
With no load applied, it will be somewhat higher than it would be under 
normal operating conditions (but the regulated output is still regulated and 
shouldn't vary).  But it's easier to just measure the rectified and filtered 
DC voltage: just measure across the tantalum capacitor.  Since the 7915 has 
a 2 volt margin, the input must be at least 17 volts under loaded conditions 
for it to operate properly.  With no load, maybe 18-19.  Voltages above that 
are fine as well, but the excess must be dissipated by the regulator: the 
higher the voltage, the hotter it runs.  The regulator can handle up to 35V, 
something close to that is going to run very hot for even moderate current 
drain (250 mA * (35-15) = 5 W, this is way more than what you would want).

_________________________________________________________________
Live Search Maps \ufffd find all the local information you need, right when you 
need it. http://maps.live.com/?icid=hmtag2&FORM=MGAC01

Thanks all,

voltages are ok once the entire system is connected to the PS,
there was a short on the lower board but it is solved now.

I got more issues with the voice card assignments but I'm still 
checking into it




--- In vintagesynthrepair@yahoogroups.com, "Scott Nordlund" 
<gsn10@...> wrote:
>
> >What I mean is, does the tantalum cap get fried because there is a
> >short between the -15v and ground caused at one of the boards, or 
the
> >only possible reason is high secondary transformer voltages which
> >overheat the 7915 regulator ?
> 
> Short answer: Neither.  The cap fried most likely because there was 
too much 
> voltage applied to it (transformer secondary is too high, excessive 
mains 
> voltage, whatever).  If this is in excess of the rated voltage, it 
will 
> fail, it's got nothing to do with the regulator or the load on the 
supply.
> 
> Longer answer: It might be possible that, given excessive current 
drain and 
> leaky filter capacitors, there was a lot of voltage ripple at that 
point and 
> thus the capacitor was placed under undue strain which made it more 
> succeptible to failure.  But I really don't buy that, it's much 
less likely.
> 
> >How do I check the secondary voltages and what should I see 
there ?...
> 
> You'll need an AC RMS voltmeter to directly measure the secondary 
voltage.  
> With no load applied, it will be somewhat higher than it would be 
under 
> normal operating conditions (but the regulated output is still 
regulated and 
> shouldn't vary).  But it's easier to just measure the rectified and 
filtered 
> DC voltage: just measure across the tantalum capacitor.  Since the 
7915 has 
> a 2 volt margin, the input must be at least 17 volts under loaded 
conditions 
> for it to operate properly.  With no load, maybe 18-19.  Voltages 
above that 
> are fine as well, but the excess must be dissipated by the 
regulator: the 
> higher the voltage, the hotter it runs.  The regulator can handle 
up to 35V, 
> something close to that is going to run very hot for even moderate 
current 
> drain (250 mA * (35-15) = 5 W, this is way more than what you would 
want).
> 
> _________________________________________________________________
> Live Search Maps – find all the local information you need, right 
when you 
> need it. http://maps.live.com/?icid=hmtag2&FORM=MGAC01
>