[sdiy] EMS VCS3 II negative power supply problems

[Mattias Rickardsson]

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...?

/mr

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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