Vintage Synth Repair

I've just refurbished my JX8P's power supply unit,
replacing all caps. I check the voltages and see
+14.40v and -14.40v instead of -15v and +15v.

The schematics shows a M5230L dual tracking regulator, two 
transistors and an array of resistors.

So far I replaced the regulator to no avail,
and verified the correct values of the various high precision 
resisotrs in the circuit, which are found to be ol.

I'm trying to figure out what could be causing this problem,
can anyone help ?....

Here's JX8P power supply schematics:
http://www.fileden.com/files/2006/10/13/285304/jx8p%20ps.JPG

..and here's M5230L datasheet:
http://www.ortodoxism.ro/datasheets/MitsubishiElectricCorporation/mXqy
yxt.pdf

Thanks in advance !

14.4 volts I would say wouldn't cause you much of a
problem anyway. It's ususally not critical. If it was
the the +5 we are talking about then it would be
different. It's common for psu voltages not to be
exact even from brand new. Do you actually have a
problem with the keyboard? 

If there is no problem with the keyboard I'd just put
it back together and leave it.

If there really is a problem with the synth then maybe
swap out the two transistors. If still a problem then
it's probably not the PSU but something in the synth
circuit that uses the +15-15 dragging the PSU down..




--- gil_we <gil_we@...> wrote:

> I've just refurbished my JX8P's power supply unit,
> replacing all caps. I check the voltages and see
> +14.40v and -14.40v instead of -15v and +15v.
> 
> The schematics shows a M5230L dual tracking
> regulator, two 
> transistors and an array of resistors.
> 
> So far I replaced the regulator to no avail,
> and verified the correct values of the various high
> precision 
> resisotrs in the circuit, which are found to be ol.
> 
> I'm trying to figure out what could be causing this
> problem,
> can anyone help ?....
> 
> Here's JX8P power supply schematics:
>
http://www.fileden.com/files/2006/10/13/285304/jx8p%20ps.JPG
> 
> ..and here's M5230L datasheet:
>
http://www.ortodoxism.ro/datasheets/MitsubishiElectricCorporation/mXqy
> yxt.pdf
> 
> Thanks in advance !
> 
> 
> 



      ___________________________________________________________
Yahoo! Answers - Got a question? Someone out there knows the answer. Try it
now.
http://uk.answers.yahoo.com/

Yep, no actual problem with the synth itself. I just feel that it 
would be generally better for the circuit to run on the correct 
volatges. It could be a little distorted as well I think....
The voltages are read when PS is not connected to the other units.

Will reaplcing the transistors do the trick ?




--- In vintagesynthrepair@yahoogroups.com, Philip <eggwheatis@...> 
wrote:
>
> 14.4 volts I would say wouldn't cause you much of a
> problem anyway. It's ususally not critical. If it was
> the the +5 we are talking about then it would be
> different. It's common for psu voltages not to be
> exact even from brand new. Do you actually have a
> problem with the keyboard? 
> 
> If there is no problem with the keyboard I'd just put
> it back together and leave it.
> 
> If there really is a problem with the synth then maybe
> swap out the two transistors. If still a problem then
> it's probably not the PSU but something in the synth
> circuit that uses the +15-15 dragging the PSU down..
> 
> 
> 
> 
> --- gil_we <gil_we@...> wrote:
> 
> > I've just refurbished my JX8P's power supply unit,
> > replacing all caps. I check the voltages and see
> > +14.40v and -14.40v instead of -15v and +15v.
> > 
> > The schematics shows a M5230L dual tracking
> > regulator, two 
> > transistors and an array of resistors.
> > 
> > So far I replaced the regulator to no avail,
> > and verified the correct values of the various high
> > precision 
> > resisotrs in the circuit, which are found to be ol.
> > 
> > I'm trying to figure out what could be causing this
> > problem,
> > can anyone help ?....
> > 
> > Here's JX8P power supply schematics:
> >
> http://www.fileden.com/files/2006/10/13/285304/jx8p%20ps.JPG
> > 
> > ..and here's M5230L datasheet:
> >
> 
http://www.ortodoxism.ro/datasheets/MitsubishiElectricCorporation/mXqy
> > yxt.pdf
> > 
> > Thanks in advance !
> > 
> > 
> > 
> 
> 
> 
>       ___________________________________________________________
> Yahoo! Answers - Got a question? Someone out there knows the 
answer. Try it

> now.
> http://uk.answers.yahoo.com/
>

I really wouldn't worry then..these things are
designed to run within a range of voltages...ie
tolerance +-20%.. the +15 -15 is for the Op amps I
would have thought..they'll be quite happy with a nice
a current at 14.4v. The transistors could make a
difference yes but I doubt they actually will..the
main contenders are the caps and the regulator which
you've already changed.

Put it back together is my advice... :o)

Good luck, Phil.





--- gil_we <gil_we@...> wrote:

> Yep, no actual problem with the synth itself. I just
> feel that it 
> would be generally better for the circuit to run on
> the correct 
> volatges. It could be a little distorted as well I
> think....
> The voltages are read when PS is not connected to
> the other units.
> 
> Will reaplcing the transistors do the trick ?
> 
> 
> 
> 
> --- In vintagesynthrepair@yahoogroups.com, Philip
> <eggwheatis@...> 
> wrote:
> >
> > 14.4 volts I would say wouldn't cause you much of
> a
> > problem anyway. It's ususally not critical. If it
> was
> > the the +5 we are talking about then it would be
> > different. It's common for psu voltages not to be
> > exact even from brand new. Do you actually have a
> > problem with the keyboard? 
> > 
> > If there is no problem with the keyboard I'd just
> put
> > it back together and leave it.
> > 
> > If there really is a problem with the synth then
> maybe
> > swap out the two transistors. If still a problem
> then
> > it's probably not the PSU but something in the
> synth
> > circuit that uses the +15-15 dragging the PSU
> down..
> > 
> > 
> > 
> > 
> > --- gil_we <gil_we@...> wrote:
> > 
> > > I've just refurbished my JX8P's power supply
> unit,
> > > replacing all caps. I check the voltages and see
> > > +14.40v and -14.40v instead of -15v and +15v.
> > > 
> > > The schematics shows a M5230L dual tracking
> > > regulator, two 
> > > transistors and an array of resistors.
> > > 
> > > So far I replaced the regulator to no avail,
> > > and verified the correct values of the various
> high
> > > precision 
> > > resisotrs in the circuit, which are found to be
> ol.
> > > 
> > > I'm trying to figure out what could be causing
> this
> > > problem,
> > > can anyone help ?....
> > > 
> > > Here's JX8P power supply schematics:
> > >
> >
>
http://www.fileden.com/files/2006/10/13/285304/jx8p%20ps.JPG
> > > 
> > > ..and here's M5230L datasheet:
> > >
> > 
>
http://www.ortodoxism.ro/datasheets/MitsubishiElectricCorporation/mXqy
> > > yxt.pdf
> > > 
> > > Thanks in advance !
> > > 
> > > 
> > > 
> > 
> > 
> > 
> >      
>
___________________________________________________________
> > Yahoo! Answers - Got a question? Someone out there
> knows the 
> answer. Try it
> > now.
> > http://uk.answers.yahoo.com/
> >
> 
> 
> 



      ___________________________________________________________
Yahoo! Answers - Got a question? Someone out there knows the answer. Try it
now.
http://uk.answers.yahoo.com/

Ok, thanks buddies ;)

It just courious me why the voltage would drop anyway....





--- In vintagesynthrepair@yahoogroups.com, Scott Nordlund <gsn10@...> 
wrote:
>
> 
> It's only 4% lower than the specified voltage- it really doesn't 
matter.  It could just be a result of component tolerance.  Probably 
any skilled designer wouldn't be pushing signal levels so much that a 
0.4V drop would cause any distortion.  I think you're wasting your 
time to try to "fix" this.
> 
> To: vintagesynthrepair@yahoogroups.com
> From: gil_we@...
> Date: Mon, 3 Mar 2008 12:25:27 +0000
> Subject: [vintagesynthrepair] Re: JX8P +15v and -15v voltages are 
wrong...
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
>   
> 
> 
>     
>             Yep, no actual problem with the synth itself. I just 
feel that it 
> 
> would be generally better for the circuit to run on the correct 
> 
> volatges. It could be a little distorted as well I think....
> 
> The voltages are read when PS is not connected to the other units.
> 
> 
> 
> Will reaplcing the transistors do the trick ?
> 
> 
> 
> --- In vintagesynthrepair@yahoogroups.com, Philip <eggwheatis@> 
> 
> wrote:
> 
> >
> 
> > 14.4 volts I would say wouldn't cause you much of a
> 
> > problem anyway. It's ususally not critical. If it was
> 
> > the the +5 we are talking about then it would be
> 
> > different. It's common for psu voltages not to be
> 
> > exact even from brand new. Do you actually have a
> 
> > problem with the keyboard? 
> 
> > 
> 
> > If there is no problem with the keyboard I'd just put
> 
> > it back together and leave it.
> 
> > 
> 
> > If there really is a problem with the synth then maybe
> 
> > swap out the two transistors. If still a problem then
> 
> > it's probably not the PSU but something in the synth
> 
> > circuit that uses the +15-15 dragging the PSU down..
> 
> > 
> 
> > 
> 
> > 
> 
> > 
> 
> > --- gil_we <gil_we@> wrote:
> 
> > 
> 
> > > I've just refurbished my JX8P's power supply unit,
> 
> > > replacing all caps. I check the voltages and see
> 
> > > +14.40v and -14.40v instead of -15v and +15v.
> 
> > > 
> 
> > > The schematics shows a M5230L dual tracking
> 
> > > regulator, two 
> 
> > > transistors and an array of resistors.
> 
> > > 
> 
> > > So far I replaced the regulator to no avail,
> 
> > > and verified the correct values of the various high
> 
> > > precision 
> 
> > > resisotrs in the circuit, which are found to be ol.
> 
> > > 
> 
> > > I'm trying to figure out what could be causing this
> 
> > > problem,
> 
> > > can anyone help ?....
> 
> > > 
> 
> > > Here's JX8P power supply schematics:
> 
> > >
> 
> > http://www.fileden.com/files/2006/10/13/285304/jx8p%20ps.JPG
> 
> > > 
> 
> > > ..and here's M5230L datasheet:
> 
> > >
> 
> > 
> 
> 
http://www.ortodoxism.ro/datasheets/MitsubishiElectricCorporation/mXqy
> 
> > > yxt.pdf
> 
> > > 
> 
> > > Thanks in advance !
> 
> > > 
> 
> > > 
> 
> > > 
> 
> > 
> 
> > 
> 
> > 
> 
> >       __________________________________________________________
> 
> > Yahoo! Answers - Got a question? Someone out there knows the 
> 
> answer. Try it
> 
> > now.
> 
> > http://uk.answers.yahoo.com/
> 
> >
> 
> 
> 
> 
>       
> 
>     
>     
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> _________________________________________________________________
> Connect and share in new ways with Windows Live.
> http://www.windowslive.com/share.html?
ocid=TXT_TAGHM_Wave2_sharelife_012008
>

Have you considered the possibility that the multimeter is not as accurate as you thought?  Most would be no better than 1% or 2% and even then when was the

Have to tested the voltage under load.  That is more important to see if the whole PS is acutally working and regulating.

Regards;

Peter

Hi, 
I have just looked at the PSU drawing. (I could not get the data sheet 
to open.) Anyway,for what its worth and from using these in the past, 
R4 and R5 make sure the + and - lines sit equally about the 0 
volt/ground line. The output voltage is set by R3 and R7 with a final 
trim of R7 if an exact voltage is needed. Was your voltage ever exactly 
15 volts. If not, provided that the DC voltages on C1 and C2 are above 
+17 and -17 volts, then just forget it. Your PSU output voltages are 
fine and so are TR1 and TR2. 
JohnB

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

>
> Ok, thanks buddies ;)
> 
> It just courious me why the voltage would drop anyway....
> 
> 
> 
> 
>

Thanks !

--- In vintagesynthrepair@yahoogroups.com, "johnx66uk2003" <john@...>
wrote:

>
> Hi, 
> I have just looked at the PSU drawing. (I could not get the data sheet 
> to open.) Anyway,for what its worth and from using these in the past, 
> R4 and R5 make sure the + and - lines sit equally about the 0 
> volt/ground line. The output voltage is set by R3 and R7 with a final 
> trim of R7 if an exact voltage is needed. Was your voltage ever exactly 
> 15 volts. If not, provided that the DC voltages on C1 and C2 are above 
> +17 and -17 volts, then just forget it. Your PSU output voltages are 
> fine and so are TR1 and TR2. 
> JohnB
> 
> --- In vintagesynthrepair@yahoogroups.com, "gil_we" <gil_we@> wrote:
> >
> > Ok, thanks buddies ;)
> > 
> > It just courious me why the voltage would drop anyway....
> > 
> > 
> > 
> > 
> >
>