[sdiy] EMS VCS3 II negative power supply problems

Mattias Rickardsson mr at analogue.org
Fri Sep 16 23:53:49 CEST 2022

Hej Magnus,

yes, the power transistors are off board, and I've replaced that one. Also
the nearby metal can transistor. There's also a third transistor in regular
small plastic package close to them that I'm not completely sure at the
moment what it does in the negative power circuit...?


Den fre 16 sep. 2022 21:57Magnus Danielson <magnus at rubidium.se> skrev:

> Hi,
> Check the buffer transistor. That had blown on mine.
> The Mark II PSU is nicer than the Mark I PSU for VCS3/Synthi-A.
> About the same time as the Mark I and Mark II shift, they moved the
> transistors off the PSU board. If they are on the board, move them out as
> this remove heat and it will eventually fail. Guess how I know.
> Cheers,
> Magnus
> On 2022-09-13 21:50, Mattias Rickardsson wrote:
> Hey,
> I'm trying to revive a VCS3 II where the power supply has issues on the
> negative regulation. With an incoming -25 V it puts out roughly -24 V
> instead of the supposed -9 V. Does anyone have experience with similar
> problems?
> (The transformer was fried on the negative half, so I'm running it from a
> bench supply. I have also replaced the regulating 741 and TIP3055 power
> transistor)
> ((The phutney.com site and its very readable schematics also magically
> disappeared, which didn't help)) :-)
> Best,
> /mr
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