[sdiy] Questioning on why both of this power transformer primary windings went almost short..

[Michael E Caloroso]

Also make sure that the earth on the line voltage is NOT directly connected
to any of the secondaries.  Your schematic shows four secondary windings
and none of the coil wires will be the same potential as earth, which will
cause excess current flow when directly coupled.

MC

On Fri, Feb 20, 2026 at 9:50 AM Jean-Pierre Desrochers via Synth-diy <
synth-diy at synth-diy.org> wrote:

> There are wire links that set the correct AMERICA 120v voltages on the
> same PCB. These links are placed correctly.
>
>
>
> *De :* Synth-diy <synth-diy-bounces at synth-diy.org> *De la part de* grant
> musictechnologiesgroup.com
> *Envoyé :* 19 février 2026 22:11
> *À :* synth-diy at synth-diy.org
> *Objet :* Re: [sdiy] Questioning on why both of this power transformer
> primary windings went almost short..
>
>
>
> I repaired a Garnet amp that blew its transformer when the generator it
> was hooked up to had been set for way too high a voltage (I don't remember
> what the customer said the voltage was, but they admitted the festival was
> smokier than originally planned). I think that was all that was wrong too.
> Aside from fuses.
>
> GB
>
> On 2/19/2026 5:20 PM, Jean-Pierre Desrochers via Synth-diy wrote:
>
> A customer brought me a guitar preamp that he said ‘blows its internal
> fuses..’
>
> I checked the internals and found that both of the internal 315mA primary
> windings fuses were blown (F2 & F3).
>
> The main 500mA fuse (F1) was ok.
>
> So I connected my variac to *only one* of the primary windings (no fuses)
> to find that
> reaching around 90VAC it started to drain around 1 AMP !
>
> I checked the other primary winding alone and it behaved exactly the same,
>
> 1AMP at around 90VAC.
>
> These measures were done with none of the secondaries connected (free
> wires).
>
>
>
> So my questioning is what the heck almost shorted each of these primary
> windings
> exactly the same way..?
>
> I connected external AC voltages to each of the secondaries bridge (one at
> the time)
> and there were no shorts on each of them. The resulting DC voltages were
> as expected.
>
> To create those shorts at each primaries it would have needed
> that the 315mA fuses would have been replaced by much higher values
> with some kind of shorts somewhere in the secondaries side.. ?
>
> OR this is a manufacturing default that waited to awake ?
>
> Anyway I ordered a new transformer replacement, but I don’t want
> to fry it again because of something else that blew the first one..
>
>
>
> What do you think ?
>
>
>
>
>
>
>
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