Vintage Synth Repair

Thank you ;)

Well here aew the results -

1. 5v, 15v anb -15v are all ok.

2. D4 does not show an "open" connectivity between its legs.

3. ~ to ~ on D4 shows 11v AC...

So you think that Q2 went bad, cusing the +7v unregulated voltage to 
become 11v (DC) ?

I just replaced a bad FIP display coil driver on that unit,
and wondering if the bad unregulated voltage is what made it fail in 
the first place....


--- In vintagesynthrepair@yahoogroups.com, "John Brewer" <john@...> 
wrote:
>
> First of all, the circuit is a bit unusual in as much as the feed 
for the 5v
> regulator circuit is taken
> from the +15v rail.  This is ok to a point but if Q2 fails, 15 
volts could
> and will feed back through Q1. This would only be limited by R2 
giving about
> 11 volts on the 7 volt rail.  You could try removing Q2 as a start 
to see
> what happens.
> OK, Can you do a few things to track the problem down.
> 1) Is the 5 Volts correct? Is the +15 and -15 correct?
> 2) have you checked D4.
> 3) What is the AC voltage between ~ and ~?
> 
> Ignore for the moment the 'AC' reading you are getting.  This could 
be a red
> herring depending on the model test meter you are using.
> Best regards.
> John. (U.K., where are you?)
> 
> ----- Original Message -----
> From: "gil_we" <gil_we@...>
> To: <vintagesynthrepair@yahoogroups.com>
> Sent: Sunday, August 20, 2006 12:22 AM
> Subject: [vintagesynthrepair] What causes bad unregulated voltage 
on the
> power supply ?
> 
> 
> > I got a Roland MKS70 of which the Power Supply unregulated 
voltage rail
> > is too high. The schematics says there should be +7v but I read 11
V
> > when the DMM is set to DC and 28v when set to AC !
> >
> > This fits with the fact that the display of that unit is 
overbright,
> > showing all characters at once....
> >
> > But what can cause the unregulated voltage to be incorrect ?
> > could this be bad regulators in the PS unit ??
> >
> > I already replaced all capacitors in the PS.
> >
> > Thanks all !!
> >
> >
> >
> >
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> > Yahoo! Groups Links
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