[sdiy] EMS VCS-3/Synthi-A Mk I hint

[Magnus Danielson]

Dear all,

(Beware of the cross-positing! Answer to "your" email-list.)

The VCS-3 Mk I and Synthi A Mk I has a really ugly design-flaw: It's PSU.
Actually, the PSU has multiple design-flaws, but some of them are worse than
others. In particular, the Mk I A-board is built such that all power-burning
occurs in one place and the heat-sink for the TIP31C covers the other
components and creates a local heat-source.

For a Synthi A I strongly recommend moving the TIP31A to the top of the metal
frame and extend it's leads with wire and have a connector so that one can
disconnect the board for servie. Also, remove the heat-sink for the TIP31C from
the A-board, it will allow the air to more freely dissapate the heat from the
remaining resistors and transistors. Also, the resistor in series with the
diode-bridge (between the 1000 uF and 2400 uF caps) should be a heat-sink
friendly one mounted on the side of the metal frame.

The end-result is that now are all the power-sources distributed in space, they
get a good chance of dissapating their heat and no excessive temperatures is
built up.

Naturally should one take the chance to replace the caps.

Oh, beware of the possible bad soldering joints on the A-board's PSU part.
Possibly should all be refreshed, the heat and heat-induced mechanical stress
make them age prematurely!

I strongly recommend doing this fix, if one is fairly handy with a soldering
iron. The Mk I Synthi A that I fixed feels much more safer after this.

Cheers,
Magnus