Vintage Synth Repair

On Sunday 04 May 2008 17:14, Malte Rogacki wrote:
> I've heard about the problem with the "potentially 30V" issue but cannot
> really see how this would happen - at least not for the main gating circuit
> and the power supply decoupling. But then I'm not really fluent in those
> things; so I would be glad if someone could give me an explanation (I'm
> always eager to learn about this stuff).

It took a little digging since I don't seem to have my ARP stuff handy here,  
but I found my electronic copies of the schematic (which are nowhere near as 
handy for flipping back and forth quick between multiple diagrams...)

If you look at say the Upper Voicing Board where those 22uF caps are used, 
you'll see a point that's marked 0V for short release,  and -15V for long 
release.  This is incorrect!  That same error comes up in two different 
places,  I forget where the other one is.

Following that from the source,  which is the upper right corner of the Lower 
Voicing Board schematic,  you can see that point near the sustain footswitch 
jack and some transistors and whatnot quite plainly marked "+15V".  Since the 
negative end of all those tantalum caps is tied to -15V,  then what appears 
at the top end of them is going to depend on where you have the release 
slider set -- have it set for the longest release time and you'll have 30V 
across all those 25V tantalum caps.

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin