Vintage Synth Repair

Thanks for all answers to my questions.

Daniel Forro


On 9 Apr, 2013, at 5:00 AM, shupac800 wrote:

> Alexis has it right -- tantalums were used because they pack a lot  
> of capacitance into a very small package.  (Low ESR is good too.)   
> Tantalums are used a lot in cell phones now for the same reason.   
> Now electrolytics in the 1-22 uF range can also be made very small,  
> which was not the case in 1980.
>
> I have seen lots of early 80's units in which the power supply was  
> damaged because of a shorted tantalum cap.  When I work on a  
> synthesizer of this vintage, replacing all tantalums with  
> electrolytics is the first thing I do.  Pay attention to polarity --  
> both tantalums and electrolytics are polarized, so make sure the (+)  
> end of the new electrolytic goes where the (+) leg of the tantalum  
> was.
>
> I wouldn't bother adding capacitors across the power inputs of IC's.
>
> Regarding multiple capacitors -- as far as I know, multiple  
> capacitors (i.e. multiple capacitors in one can) aren't made  
> anymore, so I would wager that any you find are old and no longer  
> "fresh."  Whenever I've had to replace a multiple capacitor, I  
> replace the single multiple cap with individual capacitors of the  
> correct voltages and values.
>
> If space is a problem, get creative -- you can place the new caps  
> somewhere near the original cap location and run wires from their  
> legs to the holes in the PCB where they connect.  (Obviously, the  
> shorter the wires, the better.)  Insulate the solder joints on the  
> cap legs with electrical tape or, better, heat-shrink tubing.  Zip  
> ties or hot glue are useful for holding capacitors in place when  
> they aren't soldered directly to the board.
>
> Remember when replacing electrolytic capacitors that it's always OK  
> to replace them with same value, higher voltage rating.  Also, since  
> most electrolytics are used as ripple/spike filters, their  
> capacitance value is not critical above a certain minimum, meaning  
> that you can replace them with higher value, same voltage rating caps.
>
> --
> David Shuman