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<div class="moz-cite-prefix">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. <br>
<br>
GB<br>
<br>
On 2/19/2026 5:20 PM, Jean-Pierre Desrochers via Synth-diy wrote:<br>
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<p class="MsoNormal"><span lang="EN-CA">A customer brought me a guitar preamp that he said ‘blows its internal fuses..’<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">I checked the internals and found that both of the internal 315mA primary windings fuses were blown (F2 & F3).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">The main 500mA fuse (F1) was ok.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">So I connected my variac to <u>only one</u> of the primary windings (no fuses) to find that<br>
reaching around 90VAC it started to drain around 1 AMP !<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">I checked the other primary winding alone and it behaved exactly the same,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">1AMP at around 90VAC.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">These measures were done with none of the secondaries connected (free wires).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">So my questioning is what the heck almost shorted each of these primary windings<br>
exactly the same way..?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">I connected external AC voltages to each of the secondaries bridge (one at the time)<br>
and there were no shorts on each of them. The resulting DC voltages were as expected.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">To create those shorts at each primaries it would have needed<br>
that the 315mA fuses would have been replaced by much higher values<br>
with some kind of shorts somewhere in the secondaries side.. ?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">OR this is a manufacturing default that waited to awake ?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">Anyway I ordered a new transformer replacement, but I don’t want<br>
to fry it again because of something else that blew the first one..<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">What do you think ?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><img width="802" height="301" style="width:8.3541in;height:3.1354in" id="Image_x0020_1" src="x-moz-ews://grant%40musictechnologiesgroup.com@outlook.office365.com/Inbox/1217?header=quotebody&part=1.1.2&filename=image003.jpg"><o:p></o:p></p>
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