Death of a Serge

[jh.]

> .. late last week my Serge stopped making sound.. so yesterday I popped it
> out of the case, powered it up.. only to see smoke start pouring out of a
> capacitor!
>
> Now I'm trying to decide what to do. Obviously I will test the power
> supply, but I doubt that the new Power One supply I put in is bad. Seems
> more likely that the cap itself failed, and is shorting the supply..
though
> there may be more wrong.
>
> I realize that schematics of this are closely held secrets, that repair
can
> only be done by one man, and that he is currently on some extended
> life-examining pilgrimage in the Upper Midwest. However, maybe somebody
out
> there who has puzzled through these things in the past can help me. The
cap
> in question is a ceramic disk on the Variable Q VCF board, about halfway
> down, between a 100K trimpot and am LM3080. It's right next to the +15v
> line, so I bet it is a decoupling cap. Can anyone confirm this?


Hi Jim,

maybe there is hope.
I don't know the circuit in question, but sometimes repair *without* knowing
the circuit is possible, when you know exactly which component failed.
So the first thing I'd try would be replacing that capacitor, and then
connecting
the module to a lab power supply with a low current limit selected.

You may be lucky (I have repaired two Crumar Performers by just replacing
blown bypass caps, without schemos). If you're not lucky, if the module died
from overvoltage, connecting it to a current limited supply will probably
not cause much extra damage. For the worst case, how many chips does
the module contain ? What would replacing them *all* cost ? Serge circuits
are renowned for brilliant circuit designs rather than using heaps of
expensive
chips. Which leaves the calibration, of course. But it might be easier to
get calibration hints than the entire schematics. Maybe. I'm just
theoretically
speaking.

There might be another possibility. I can imagine there are some people who
would gladly take a look at Serge modules and draw a schematic diagram
directly from the board. (No, *I* am out of the question, I'm living in
Europe (;->) ) Maybe you find someone in your region who is curious as
well.

Good luck !

JH.