Vintage Synth Repair

Thanks John, back to the list.

I added the scheme for the display board to the Files section.
As you can see, there's something strange - the two +7v wires at the 
connector, connect to... nothing ! The connector goes to the Assigner 
board. I marked the +7v and the coil with red arrows.

If I understand you correctly - the 12/11v is what I SHOULD read by 
the circuit design ??? So you're saying that the +7 information is 
wrong ??....

What I'm mostly worried about is that some other bad component will 
defect the new display coil that I put. I dunno if I can get any 
other replacement ! I've been working on that display for weeks !

Thanks again.




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RE:

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Hi,

No problem, continue to post to the list. I can't post to the list 
from here but I can get the messages off so that is not a problem. 

You will notice that the 7 volts only goes to the Jack board and the 
assigner board.  Does the FIP live on either of these?  If not then 
it will not be affected by the 7V issue. Do you have the diagram for 
CN3 that you can put in the files section.  I am beginning to smell a 
rat as they say :-).   You have measured the ~ ~ points on D4 and 
that was 11 volts AC. If the D4 bridge is correctly fitted and is OK 
then you would expect the loaded voltage to be around 12 volts DC 
across C11 and not 7 Volts as shown on the drawing.    Can you check 
the individual diodes in D4 with your ohmmeter. two face one way from 
the ~s to - and two face the other way from ~s to +. There is 
something spooky going on here. As the 5V is OK then Q1 and Q2 must 
also be OK.  Best regards. John.

 




--- In vintagesynthrepair@yahoogroups.com, "Gil W." <gil_we@...> 
wrote:
>
> Thanks John,
> 
> I don't have your regular address so I'm posting back
> to the list...
> 
> I tried to replace both D4 and Q2 (with substitutes)
> and got 0 voltage on the 5v rail, if I remember
> correctly (I might be wrong but either the 5v or 7v
> rails were 0). Not to cause any further damage I put
> the original back... Should I replace only D4 and try
> again ? Are there any parts which may cause it ? 
> 
> I just fixed the display problem I had on that unit
> and it became that the bad component was a coil which
> acts as FIP (fluorescent display) driver. I wonder if
> that was caused by the bad unregulated voltage... if
> so, I will have to fix that otherwise the new coil
> will go bad as well...
> 
> 
> 
> 
> --- John Brewer <member@...> wrote:
> 
> > Hi, I am replying off list from a host computer via
> > web mail.  Please continue to reply to my usual
> > address.
> > If you have 11v Ac. on D4 then I would expect what
> > is marked as 7 Volts to be nearer 18 volts or more
> > because of the C11 charging to peak. Something very
> > strange indeed is happening!!  Remove D4 completely
> > then measure the 7 volt line again. It should be
> > zero.  Have you checked the individual diodes in D4
> > and is it correctly inserted in the board.
> > If the 5 Volts is OK, then Q2 is ok and not feeding
> > back positive voltage to the unregulated line.  The
> > mistery deepens. 
> > Best regards, John.
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > ========================================
> > Message Received: Aug 22 2006, 06:22 PM
> > From: "gil_we" 
> > To: vintagesynthrepair@yahoogroups.com
> > Cc: 
> > Subject: [vintagesynthrepair] Re: What causes bad
> > unregulated voltage on the power supply ?
> > 
> > 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" 
> > 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" 
> > > To: 
> > > 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 !!
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > Yahoo! Groups Links
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > --
> > > > Internal Virus Database is out-of-date.
> > > > Checked by AVG Free Edition.
> > > > Version: 7.1.394 / Virus Database: 268.10.7/409
> > - Release Date: 
> > 04/08/06
> > > >
> > > >
> > >
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > Yahoo! Groups Links
> > 
> > 
> > vintagesynthrepair-unsubscribe@yahoogroups.com
> > 
> 
> 
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