On 9/22/2015 4:40 PM, John Larkin wrote:
On Tue, 22 Sep 2015 12:56:56 -0700, Jeff Liebermann
wrote:

On Tue, 22 Sep 2015 15:34:51 -0400, bitrex
wrote:

So I'm working on repairing a Korg MS2000B synthesizer for a friend with
a dead power supply. Here's the service manual:

http://www.loscha.com/scans/Korg_MS2...ice_Manual.pdf

The first thing I notice when looking inside is that the small SMT 100uF
10V tantalum capacitor C109 has completely vacated - it appears to be
gone, blown right off the board. There are some little fragments
rattling around in the case.

I have little experience with tantalum capacitors. Any suggestions for
a more reliable replacement?

I don't think there's a reliability issue here. C109 (located on the
Power / MIDI board schematic, is the initial output filter capacitor
in a 3.3V switching power supply. There are other 100 uf caps
surrounding it, but it seems to be the only tantalum cap, which
suggests that the designer needed some specific characteristic of the
cap to make things work. Methinks a change of capacitor type might
not be such a great idea.

What would make the cap explode? My guess(tm) is that someone plugged
in a wrong voltage power supply, which blew up FET (F1) which then
applied overvoltage to the tantalum. It much have been quite a large
jolt as tantalums using produce a low resistance "short" which then
gets hot and starts smoking toxic fumes. I would look around for
other parts in the power supply section that may be been destroyed,
such as the other caps along the 3.3V rail.

Dry-slug tantalums across power rails are bad news. High dV/dT
literally ignites them; MnO2 is the oxidizer and tantalum is the fuel.

Derate them 3:1 on voltage, or use something else. Polymer aluminums
are good, and some come in a tantalum-like surface mount package.


Is there anything I can use temporarily in its place, that I might have
in stock, to try and get that switcher up and running while I wait for
the appropriate part?