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<p>Hej Mattias,</p>
<p>It's a classic over-current protection setup. So if there is too
much current it will make the driver back off. If this is broken
you god that happening you the supply. <br>
</p>
<p>Cheers,<br>
Magnus<br>
</p>
<div class="moz-cite-prefix">On 2022-09-16 23:53, Mattias
Rickardsson wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAP92RBV6noUKZDPx7cByfLCtgdvUYXL=Td6huMAUVjLmegY7Zg@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="auto">Hej Magnus,
<div dir="auto"><br>
</div>
<div dir="auto">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...?</div>
<div dir="auto"><br>
</div>
<div dir="auto">/mr</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">Den fre 16 sep. 2022
21:57Magnus Danielson <<a href="mailto:magnus@rubidium.se"
moz-do-not-send="true" class="moz-txt-link-freetext">magnus@rubidium.se</a>>
skrev:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<p>Hi,</p>
<p>Check the buffer transistor. That had blown on mine.</p>
<p>The Mark II PSU is nicer than the Mark I PSU for
VCS3/Synthi-A.</p>
<p>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.<br>
</p>
<p>Cheers,<br>
Magnus<br>
</p>
<div>On 2022-09-13 21:50, Mattias Rickardsson wrote:<br>
</div>
<blockquote type="cite">
<div dir="auto">Hey,
<div dir="auto"><br>
<div dir="auto">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?</div>
<div dir="auto"><br>
</div>
<div dir="auto">(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)</div>
<div dir="auto"><br>
</div>
<div dir="auto">((The <a href="http://phutney.com"
target="_blank" rel="noreferrer"
moz-do-not-send="true">phutney.com</a> site and
its very readable schematics also magically
disappeared, which didn't help)) :-)</div>
<div dir="auto"><br>
</div>
<div dir="auto">Best,</div>
<div dir="auto"><br>
</div>
<div dir="auto">/mr</div>
<div dir="auto"><br>
</div>
</div>
</div>
<br>
<fieldset></fieldset>
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