Vintage Synth Repair

Well then best of luck with your repair. After all the work you've done to your psu, you deserve the right to succeed ! :)

I will have to recap my cs-70m's power supply (still working fortunately), because it's all original and it takes some time for it to warm-up (too long actually), and the volume pot is noisy when you turn it, but it's not a dirty pot because noise almost disappears when the synth is warmed-up.

I want to install the kenton midi kit that I have for it, but will do once everything -or at least the psu- be properly recapped...

You just don't want to open those beasties to often ;)



--- In vintagesynthrepair@yahoogroups.com, Adrian Corston <eidorian@...> wrote:
>
> Thanks for the multimeter suggestion, but I decided it was past time to 
> get the CRO (a Tektronics 465M) out anyway so I could have a good look 
> around and be sure.  The shed needs a bit of cleanup now, but to be 
> honest it's probably not that much worse than it was before anyway :-)
> 
> On the -26V and +26V coming from the rectifier bridge I measure about 
> 0.05V ripple each, which seems very reasonable.  On all the test points 
> (+5V, +10V, -5V and the faulty +15V and -15V) I can't see any 
> appreciable ripple at all (even with the scope resolution wound right 
> up).  So it looks like that is not the issue with this supply.
> 
> However, your suggestion is another good thing to check on future 
> repairs, so thank you very much for that!
> 
> Cheers,
> A.
> 
> 
> On 2/08/13 6:01 PM, cpt.zilog wrote:
> >
> > All right and thanks for your message(s)!
> >
> > You don't have to use a scope to test for AC leakage. A multimeter can 
> > do the job. Set it to AC voltage test and probe the DC output tabs of 
> > the rectifier bridge. If you get a significant reading, then you know 
> > that the bridge is toasted.
> >
> > I think it make sense for a PSU this age (and with an obvious problem) 
> > to replace all passive components at first such as electrolytics which 
> > are essential for stability (all of them, starting with the big 
> > regulating ones), and test others like you did for resistors, as an 
> > example. Once you're sure about the reliability of your passives, you 
> > can tackle your actives (transistors, IC, etc...)
> >
> > --- In vintagesynthrepair@yahoogroups.com 
> > <mailto:vintagesynthrepair%40yahoogroups.com>, eidorian@ wrote:
> > >
> > > I'm sorry, not at all! I just haven't been able to get to my venerable
> > > old Tektronics CRO, which is buried at the rear of my shed behind an
> > > enormous pile of junk that is too unstable to climb over :-(
> > >
> > > Your advice is excellent; my failure to follow it is the only thing
> > > lacking. Please accept my apology, I appreciate your help.
> > >
> > > Cheers,
> > > A.
> > >
> > >
> > > On 2013-08-01 08:20, cpt.zilog wrote:
> > > > Excuse me but I'd like to know if I did say something false or stupid
> > > > in my previous message ?
> > > > Don't want to sound rude, but if my idea is wrong, my ego can handle
> > > > it as long as someone corrects me (and write it!) ;)
> > > > Thanks
> > > >
> > > > >
> > > > > --- In vintagesynthrepair@yahoogroups.com 
> > <mailto:vintagesynthrepair%40yahoogroups.com>, "cpt.zilog"
> > > > <cpt.zilog@> wrote:
> > > > > >
> > > > > > Hello guys and sorry to jump in like that but I would suggest to
> > > > change the big caps as a priority and then check the bridge rectifier
> > > > again for leakage of AC current.
> > > > > >
> > > > > > I had a big problem with a D&R console's psu in which the
> > > > voltage regulators kept on going Kapput. Turned out that the big
> > > > Electrolytics were bad and that induced a big stress on the rectifier
> > > > bridge, which in turn had the consequence of not only letting DC pass
> > > > as expected, but also AC at the same time !
> > > > > >
> > > > > > I did test for AC leakage on the rectifier after the newly
> > > > installed voltage regulator worked for a couple of seconds before
> > > > shorting...
> > > > > >
> > > > > > After new BIG caps, new bridge rectifier and a 2nd new voltage
> > > > regulator, everything was sorted.
> > > > > >
> > > > > > Good luck !
> > > > > >
> > > > >
> > >
> >
> >
>