Vintage Synth Repair

Cleaning the keyboard contact with alcohol cleaner, I could play for a couple of hours without seeing the problem. How likely that this was caused by bad key contacts ? how does this (resistance) affect the pitch ?



--- In vintagesynthrepair@yahoogroups.com, "lhammond" <lhammond@...> wrote:
>
> I use felt pipecleaners as you can bend them around contacts and they
> absorb cleaning liquids.  But the best is to pullthe rodd and buff it on
> the sort of machine a jeweller will have.  And rotate it if worn.
> 
> lorne
> 
> > The pitch changes as a key go down indicates a resistive connection
> > between the contact and bus rod.  Often they are worn, sometimes damage
> > through bad maintenance.  There are many ways to correct, some very
> > imaginative to stupid.  The bus and contact have a thin gold plating,
> > once worn off, problem area. 
> >
> >
> > I remove the bus rod to allow better access to the keys side contact.  A
> > good desoldering skill set is required as the plastic can be damaged by
> > too much heat .  Sometime I just rotate it 90 degrees to give a new gold
> > area to contact.  One guy told me he used unwaxedd, so dental floss wet
> > with contact cleaner and sawed it back and forth.  Main thing, as the
> > contact strikes, you do not want changes, as voltage equals pitch.
> >
> > Drill a hole in the pot with a small drill to allow pot spray to be shot 
> > in. Insert the drill into the chuck so only an 1/8 inch sticks out, cut
> > off or grind off if to long.  This prevent the drill from going to far
> > into the pot and doing damage.  The metal is hard, so patience.
> >
> > R
> >
> >
> >
> >
> >>________________________________
> >> From: Gil <gilwe@...>
> >>To: vintagesynthrepair@yahoogroups.com
> >>Sent: Monday, July 9, 2012 8:40 AM
> >>Subject: [vintagesynthrepair] Re: Minimoog D pitch drifting
> >>
> >>
> >>Â 
> >>Hi all !
> >>
> >>So I received it a week ago and did the following -
> >>1. I took all PCB's out and cleaned the connectors
> >>2. I rewires a few bad solder joints going to the pitch and modulation
> >> wheels
> >>3. I cleaned the PCB sockets and checked for tight connectivity between
> >> the PCB's and flags
> >>4. Replaced the 1458 ICs in the generic tuning circuit (where the Tune
> >> pot goes)
> >>
> >>I see the tuning problem less then before but it still happens from time
> >> to time. I *think* it happens more when playing certain keys in the
> >> middle of the keyboard (although I don't see why it will only happen when
> >> playing this specific area). sometimes, the pitch will raise and fall as
> >> I push some keys down (like when using after-touch) - can bad kayboard
> >> PCB cause this ?
> >>
> >>Also, in the specific machine, the master Tune potentiometer doesn't
> >> reflect the tune. The "default" tunning is a down that what it should be.
> >> The Tune pot shows correct resistance values when rotating it, and the
> >> soldering and connection to the sockets (and then PCB) looks ok... Which
> >> is weird. Also, tapping on the pot, it doesn't seem to reflect the tuning
> >> at all, as if it is dead... but it is not :/
> >>
> >>--- In vintagesynthrepair@yahoogroups.com, "Paulo Palmieri"
> >> <paulopalmieri@> wrote:
> >>>
> >>> That´s right. To affect the 3 oscillators maybe the countour generator
> >>> could be the problem or the PCB conectors already commented here.
> >>> This is the late version more stable than the first generation.
> >>>
> >>> Good luck and be in touch!
> >>>
> >>> Paulo Palmieri
> >>>
> >>>
> >>>   ----- Original Message -----
> >>>   From: Quazimodo
> >>>   To: vintagesynthrepair@yahoogroups.com
> >>>   Sent: Friday, June 29, 2012 4:51 PM
> >>>   Subject: [vintagesynthrepair] Re: Minimoog D pitch drifting
> >>>
> >>>
> >>>
> >>>   So it's a late, *stable* one... OK, then it will probably be much
> >>> like I said in the first place.
> >>>
> >>>   Check those flags...!
> >>>
> >>>   --- In vintagesynthrepair@yahoogroups.com, "Gil" <gilwe@> wrote:
> >>>   >
> >>>   >
> >>>   > Thanks. Serial is 12044. Supposed to get it in a few days so I'll
> >>> be able to tell what it exactly uses (or do you know be the serial
> >>> number?)
> >>>   >
> >>>   >
> >>>   > --- In vintagesynthrepair@yahoogroups.com, "Paulo Palmieri"
> >>> <paulopalmieri@> wrote:
> >>>   > >
> >>>   > > Hi Gil,
> >>>   > >
> >>>   > > Probably there is a variation in the cv voltage that controls the
> >>> oscillators.
> >>>   > > I experienced similar issues on the osc 1 of a RA Moog model (the
> >>> first earlier version) and the only thing that solved the problem
> >>> was replacing the 2n4058 transistors.
> >>>   > > Please, provide more info such like serial number and if your
> >>> oscillator board has only transistors or 2 ICS SG3821 or
> >>> CA/LM3046 or 3 UA726 ICs.
> >>>   > >
> >>>   > > Regards,
> >>>   > >
> >>>   > > Paulo Palmieri
> >>>   > >
> >>>   > >
> >>>   > > ----- Original Message -----
> >>>   > > From: Gil
> >>>   > > To: vintagesynthrepair@yahoogroups.com
> >>>   > > Sent: Thursday, June 28, 2012 9:55 AM
> >>>   > > Subject: [vintagesynthrepair] Minimoog D pitch drifting
> >>>   > >
> >>>   > >
> >>>   > >
> >>>   > > I'm handling a friend's mini, which acts strangely. The overall
> >>> pitch (of the entire machine) will change suddenly, up and down,
> >>> not to far from the correct pitch but a few semitones... It
> >>> affects all oscillators at the same time. Is this a known issue
> >>> in old minimoogs? I would usually suspect either power supply
> >>> main voltage instability, bad caps or transistors, but being it
> >>> affecting all 3 oscillators, I tend to think it is not oscillator
> >>> circuit related ? :/ I'm new to minimoogs so any help would be
> >>> appreciated... Thanks !
> >>>   > >
> >>>   >
> >>>
> >>
> >>
> >>
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> >>
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