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--></style></head><body lang=FR-CA link="#0563C1" vlink="#954F72" style='word-wrap:break-word'><div class=WordSection1><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that the 315mA fuses would have been replaced by much higher values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="cid:image003.jpg@01DCA1DD.28EBF930"><o:p></o:p></p></div></body></html>